Red Hat | CLUSTER SUITE - CONFIGURING AND MANAGING A CLUSTER 2006 | Installation guide | Red Hat CLUSTER SUITE - CONFIGURING AND MANAGING A CLUSTER 2006 Installation guide

Red Hat Cluster Suite
for RHEL 4
Overview
Red Hat Cluster Suitefor RHEL 4: Overview
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Table of Contents
About This Document........................................................................................................ i
1. Document Conventions ........................................................................................ i
2. Feedback .............................................................................................................. v
1. Red Hat Cluster Suite Overview ..................................................................................1
1.1. Cluster Basics....................................................................................................1
1.2. Red Hat Cluster Suite Introduction ...................................................................2
1.3. Cluster Infrastructure ........................................................................................4
1.3.1. Cluster Management ..........................................................................4
1.3.2. Lock Management .............................................................................6
1.3.3. Fencing...............................................................................................6
1.3.4. Cluster Configuration System ..........................................................10
1.4. High-availability Service Management ..........................................................12
1.5. Red Hat GFS ...................................................................................................14
1.5.1. Superior Performance and Scalability .............................................16
1.5.2. Performance, Scalability, Moderate Price........................................17
1.5.3. Economy and Performance ..............................................................18
1.6. Cluster Logical Volume Manager ...................................................................19
1.7. Global Network Block Device ........................................................................21
1.8. Linux Virtual Server .......................................................................................22
1.8.1. Two-Tier LVS Topology ..................................................................24
1.8.2. Three-Tier LVS Topology ................................................................27
1.8.3. Routing Methods..............................................................................28
1.8.4. Persistence and Firewall Marks .......................................................32
1.9. Cluster Administration GUI............................................................................33
1.9.1. Cluster Configuration Tool ...........................................................34
1.9.2. Cluster Status Tool.........................................................................38
1.10. Linux Virtual Server Administration GUI ....................................................40
1.10.1. CONTROL/MONITORING.......................................................40
1.10.2. GLOBAL SETTINGS .................................................................41
1.10.3. REDUNDANCY ...........................................................................43
1.10.4. VIRTUAL SERVERS ..................................................................44
2. Red Hat Cluster Suite Component Summary ...........................................................53
2.1. Cluster Components........................................................................................53
2.2. Man Pages .......................................................................................................59
Index.................................................................................................................................. 63
About This Document
This document provides a high-level overview of Red Hat Cluster Suite for Red Hat Enterprise Linux 4. Although the information in this document is an overview, you should have
advanced working knowledge of Red Hat Enterprise Linux and understand the concepts of
server computing to gain a good comprehension of the information. For more information
about using Red Hat Enterprise Linux, refer to the following resources:
•
Red Hat Enterprise Linux Installation Guide — Provides information regarding installation.
•
Red Hat Enterprise Linux Introduction to System Administration — Provides introductory information for new Red Hat Enterprise Linux system administrators.
•
Red Hat Enterprise Linux System Administration Guide — Provides more detailed information about configuring Red Hat Enterprise Linux to suit your particular needs as a
user.
•
Red Hat Enterprise Linux Reference Guide — Provides detailed information suited for
more experienced users to reference when needed, as opposed to step-by-step instructions.
•
Red Hat Enterprise Linux Security Guide — Details the planning and the tools involved
in creating a secured computing environment for the data center, workplace, and home.
This document contains overview information about Red Hat Cluster Suite for Red Hat
Enterprise Linux 4 and is part of a documentation set that provides conceptual, procedural,
and reference information about Red Hat Cluster Suite for Red Hat Enterprise Linux 4.
Red Hat Cluster Suite documentation and other Red Hat documents are available in HTML,
PDF, and RPM versions on the Red Hat Enterprise Linux Documentation CD and online
at the following location:
http://www.redhat.com/docs/
1. Document Conventions
In this manual, certain words are represented in different fonts, typefaces, sizes, and
weights. This highlighting is systematic; different words are represented in the same style
to indicate their inclusion in a specific category. The types of words that are represented
this way include the following:
command
Linux commands (and other operating system commands, when used) are represented
this way. This style should indicate to you that you can type the word or phrase on
the command line and press [Enter] to invoke a command. Sometimes a command
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About This Document
contains words that would be displayed in a different style on their own (such as file
names). In these cases, they are considered to be part of the command, so the entire
phrase is displayed as a command. For example:
Use the cat testfile command to view the contents of a file, named testfile,
in the current working directory.
file name
File names, directory names, paths, and RPM package names are represented this
way. This style indicates that a particular file or directory exists with that name on
your system. Examples:
The .bashrc file in your home directory contains bash shell definitions and aliases
for your own use.
The /etc/fstab file contains information about different system devices and file
systems.
Install the webalizer RPM if you want to use a Web server log file analysis program.
application
This style indicates that the program is an end-user application (as opposed to system
software). For example:
Use Mozilla to browse the Web.
[key]
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To use [Tab] completion, type in a character and then press the [Tab] key. Your terminal displays the list of files in the directory that start with that letter.
[key]-[combination]
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The [Ctrl]-[Alt]-[Backspace] key combination exits your graphical session and returns
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text found on a GUI interface
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Select the Require Password checkbox if you would like your screensaver to require
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About This Document
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top level of a menu on a GUI screen or window
A word in this style indicates that the word is the top level of a pulldown menu. If you
click on the word on the GUI screen, the rest of the menu should appear. For example:
Under File on a GNOME terminal, the New Tab option allows you to open multiple
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Instructions to type in a sequence of commands from a GUI menu look like the following example:
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Desktop
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about.html
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paulwesterberg.png
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prompt
A prompt, which is a computer’s way of signifying that it is ready for you to input
something, is shown in this style. Examples:
$
#
[stephen@maturin stephen]$
leopard login:
user input
Text that the user types, either on the command line or into a text box on a GUI screen,
is displayed in this style. In the following example, text is displayed in this style:
To boot your system into the text based installation program, you must type in the
text command at the boot: prompt.
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<replaceable>
Text used in examples that is meant to be replaced with data provided by the user
is displayed in this style. In the following example, <version-number> is displayed in this style:
The directory for the kernel source is /usr/src/kernels/<version-number>/,
where <version-number> is the version and type of kernel installed on this
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Additionally, we use several different strategies to draw your attention to certain pieces of
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or warning. For example:
Note
Remember that Linux is case sensitive. In other words, a rose is not a ROSE is not a
rOsE.
Tip
The directory /usr/share/doc/ contains additional documentation for packages installed
on your system.
Important
If you modify the DHCP configuration file, the changes do not take effect until you restart
the DHCP daemon.
Caution
Do not perform routine tasks as root — use a regular user account unless you need to
use the root account for system administration tasks.
About This Document
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Warning
Be careful to remove only the necessary partitions. Removing other partitions could result
in data loss or a corrupted system environment.
2. Feedback
If you spot a typo, or if you have thought of a way to make this document
better, we would love to hear from you. Please submit a report in Bugzilla
(http://bugzilla.redhat.com/bugzilla/) against the component rh-cs.
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rh-cs [RHCS overview](EN)-4-Print-RHI (2006-1129T16:36)
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Chapter 1.
Red Hat Cluster Suite Overview
Clustered systems provide reliability, scalability, and availability to critical production services. Using Red Hat Cluster Suite, you can create a cluster to suit your needs for performance, high availability, load balancing, scalability, file sharing, and economy. This chapter provides an overview of Red Hat Cluster Suite components and functions, and consists
of the following sections:
•
Section 1.1 Cluster Basics
•
Section 1.2 Red Hat Cluster Suite Introduction
•
Section 1.3 Cluster Infrastructure
•
Section 1.4 High-availability Service Management
•
Section 1.5 Red Hat GFS
•
Section 1.6 Cluster Logical Volume Manager
•
Section 1.7 Global Network Block Device
•
Section 1.8 Linux Virtual Server
•
Section 1.9 Cluster Administration GUI
•
Section 1.10 Linux Virtual Server Administration GUI
1.1. Cluster Basics
A cluster is two or more computers (called nodes or members) that work together to perform a task. There are four major types of clusters:
•
Storage
•
High availability
•
Load balancing
•
High performance
Storage clusters provide a consistent file system image across servers in a cluster, allowing
the servers to simultaneously read and write to a single shared file system. A storage cluster
simplifies storage administration by limiting the installation and patching of applications
to one file system. Also, with a cluster-wide file system, a storage cluster eliminates the
need for redundant copies of application data and simplifies backup and disaster recovery.
Red Hat Cluster Suite provides storage clustering through Red Hat GFS.
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Chapter 1. Red Hat Cluster Suite Overview
High-availability clusters provide continuous availability of services by eliminating single
points of failure and by failing over services from one cluster node to another in case a node
becomes inoperative. Typically, services in a high-availability cluster read and write data
(via read-write mounted file systems). Therefore, a high-availability cluster must maintain
data integrity as one cluster node takes over control of a service from another cluster node.
Node failures in a high-availability cluster are not visible from clients outside the cluster.
(High-availability clusters are sometimes referred to as failover clusters.) Red Hat Cluster
Suite provides high-availability clustering through its High-availability Service Management component.
Load-balancing clusters dispatch network service requests to multiple cluster nodes to balance the request load among the cluster nodes. Load balancing provides cost-effective scalability because you can match the number of nodes according to load requirements. If a
node in a load-balancing cluster becomes inoperative, the load-balancing software detects
the failure and redirects requests to other cluster nodes. Node failures in a load-balancing
cluster are not visible from clients outside the cluster. Red Hat Cluster Suite provides loadbalancing through LVS (Linux Virtual Server).
High-performance clusters use cluster nodes to perform concurrent calculations. A highperformance cluster allows applications to work in parallel, therefore enhancing the performance of the applications. (High performance clusters are also referred to as computational
clusters or grid computing.)
Note
The cluster types summarized in the preceding text reflect basic configurations; your
needs might require a combination of the clusters described.
1.2. Red Hat Cluster Suite Introduction
Red Hat Cluster Suite (RHCS) is an integrated set of software components that can be deployed in a variety of configurations to suit your needs for performance, high-availability,
load balancing, scalability, file sharing, and economy.
RHCS consists of the following major components (refer to Figure 1-1):
•
Cluster infrastructure — Provides fundamental functions for nodes to work together as
a cluster: configuration-file management, membership management, lock management,
and fencing.
•
High-availability Service Management — Provides failover of services from one cluster
node to another in case a node becomes inoperative.
Chapter 1. Red Hat Cluster Suite Overview
3
•
Red Hat GFS (Global File System) — Provides a cluster file system for use with Red
Hat Cluster Suite. GFS allows multiple nodes to share storage at a block level as if the
storage were connected locally to each cluster node.
•
Cluster Logical Volume Manager (CLVM) — Provides volume management of cluster
storage.
•
Global Network Block Device (GNBD) — An ancillary component of GFS that exports
block-level storage to Ethernet. This is an economical way to make block-level storage
available to Red Hat GFS.
•
Cluster administration tools — Configuration and management tools for setting up, configuring, and managing a Red Hat cluster. The tools are for use with the Cluster Infrastructure components and with the High-availability and Service Management components. You can configure and manage other Red Hat Cluster Suite components through
tools for those components.
•
Linux Virtual Server (LVS) — Routing software that provides IP-Load-balancing. LVS
runs in a pair of redundant servers that distributes client requests evenly to real servers
that are behind the LVS servers.
For a lower level summary of Red Hat Cluster Suite components, refer to
Chapter 2 Red Hat Cluster Suite Component Summary.
Figure 1-1. Red Hat Cluster Suite Introduction
4
Chapter 1. Red Hat Cluster Suite Overview
1.3. Cluster Infrastructure
The Red Hat Cluster Suite cluster infrastructure provides the basic functions for a group of
computers (called nodes or members) to work together as a cluster. Once a cluster is formed
using the cluster infrastructure, you can use other Red Hat Cluster Suite components to
suit your clustering needs (for example, setting up a cluster for sharing files on a GFS file
system or setting up service failover). The cluster infrastructure performs the following
functions:
•
Cluster management
•
Lock management
•
Fencing
•
Cluster configuration management
1.3.1. Cluster Management
Cluster management manages cluster quorum and cluster membership. One of the following Red Hat Cluster Suite components performs cluster management: CMAN (an abbreviation for cluster manager) or GULM (Grand Unified Lock Manager). CMAN operates
as the cluster manager if a cluster is configured to use DLM (Distributed Lock Manager)
as the lock manager. GULM operates as the cluster manager if a cluster is configured to
use GULM as the lock manager. The major difference between the two cluster managers is
that CMAN is a distributed cluster manager and GULM is a client-server cluster manager.
CMAN runs in each cluster node; cluster management is distributed across all nodes in
the cluster (refer to Figure 1-2). GULM runs in nodes designated as GULM server nodes;
cluster management is centralized in the nodes designated as GULM server nodes (refer to
Figure 1-3). GULM server nodes manage the cluster through GULM clients in the cluster
nodes. With GULM, cluster management operates in a limited number of nodes: either
one, three, or five nodes configured as GULM servers.
The cluster manager keeps track of cluster quorum by monitoring the count of cluster nodes
that run cluster manager. (In a CMAN cluster, all cluster nodes run cluster manager; in a
GULM cluster only the GULM servers run cluster manager.) If more than half the nodes
that run cluster manager are active, the cluster has quorum. If half the nodes that run cluster
manager (or fewer) are active, the cluster does not have quorum, and all cluster activity is
stopped. Cluster quorum prevents the occurrence of a "split-brain" condition — a condition
where two instances of the same cluster are running. A split-brain condition would allow
each cluster instance to access cluster resources without knowledge of the other cluster
instance, resulting in corrupted cluster integrity.
In a CMAN cluster, quorum is determined by communication of heartbeats among cluster
nodes via Ethernet. Optionally, quorum can be determined by a combination of communicating heartbeats via Ethernet and through a quorum disk. For quorum via Ethernet, quorum consists of 50 percent of the node votes plus 1. For quorum via quorum disk, quorum
consists of user-specified conditions.
Chapter 1. Red Hat Cluster Suite Overview
5
Note
In a CMAN cluster, by default each node has one quorum vote for establishing quorum.
Optionally, you can configure each node to have more than one vote.
In a GULM cluster, the quorum consists of a majority of nodes designated as GULM
servers according to the number of GULM servers configured:
•
Configured with one GULM server — Quorum equals one GULM server.
•
Configured with three GULM servers — Quorum equals two GULM servers.
•
Configured with five GULM servers — Quorum equals three GULM servers.
The cluster manager keeps track of membership by monitoring heartbeat messages from
other cluster nodes. When cluster membership changes, the cluster manager notifies the
other infrastructure components, which then take appropriate action. For example, if node
A joins a cluster and mounts a GFS file system that nodes B and C have already mounted,
then an additional journal and lock management is required for node A to use that GFS
file system. If a cluster node does not transmit a heartbeat message within a prescribed
amount of time, the cluster manager removes the node from the cluster and communicates
to other cluster infrastructure components that the node is not a member. Again, other
cluster infrastructure components determine what actions to take upon notification that
node is no longer a cluster member. For example, Fencing would fence the node that is no
longer a member.
Figure 1-2. CMAN/DLM Overview
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Chapter 1. Red Hat Cluster Suite Overview
Figure 1-3. GULM Overview
1.3.2. Lock Management
Lock management is a common cluster-infrastructure service that provides a mechanism
for other cluster infrastructure components to synchronize their access to shared resources.
In a Red Hat cluster, one of the following Red Hat Cluster Suite components operates as
the lock manager: DLM (Distributed Lock Manager) or GULM (Grand Unified Lock Manager). The major difference between the two lock managers is that DLM is a distributed
lock manager and GULM is a client-server lock manager. DLM runs in each cluster node;
lock management is distributed across all nodes in the cluster (refer to Figure 1-2). DLM
can be the lock manager only in a cluster configured with CMAN as its cluster manager.
GULM runs in nodes designated as GULM server nodes; lock management is centralized
in the nodes designated as GULM server nodes. GULM server nodes manage locks through
GULM clients in the cluster nodes (refer to Figure 1-3). With GULM, lock management
operates in a limited number of nodes: either one, three, or five nodes configured as GULM
servers. GFS and CLVM use locks from the lock manager. GFS uses locks from the lock
manager to synchronize access to file system metadata (on shared storage). CLVM uses
locks from the lock manager to synchronize updates to LVM volumes and volume groups
(also on shared storage).
1.3.3. Fencing
Fencing is the disconnection of a node from the cluster’s shared storage. Fencing cuts off
I/O from shared storage, thus ensuring data integrity.
The cluster infrastructure performs fencing through one of the following programs according to the type of cluster manager and lock manager that is configured:
Chapter 1. Red Hat Cluster Suite Overview
•
Configured with CMAN/DLM — fenced, the fence daemon, performs fencing.
•
Configured with GULM servers — GULM performs fencing.
7
When the cluster manager determines that a node has failed, it communicates to other
cluster-infrastructure components that the node has failed. The fencing program (either
fenced or GULM), when notified of the failure, fences the failed node. Other clusterinfrastructure components determine what actions to take — that is, they perform any
recovery that needs to done. For example, DLM and GFS (in a cluster configured with
CMAN/DLM), when notified of a node failure, suspend activity until they detect that the
fencing program has completed fencing the failed node. Upon confirmation that the failed
node is fenced, DLM and GFS perform recovery. DLM releases locks of the failed node;
GFS recovers the journal of the failed node.
The fencing program determines from the cluster configuration file which fencing method
to use. Two key elements in the cluster configuration file define a fencing method: fencing
agent and fencing device. The fencing program makes a call to a fencing agent specified
in the cluster configuration file. The fencing agent, in turn, fences the node via a fencing
device. When fencing is complete, the fencing program notifies the cluster manager.
Red Hat Cluster Suite provides a variety of fencing methods:
•
Power fencing — A fencing method that uses a power controller to power off an inoperable node
•
Fibre Channel switch fencing — A fencing method that disables the Fibre Channel port
that connects storage to an inoperable node
•
GNBD fencing — A fencing method that disables an inoperable node’s access to a
GNBD server
•
Other fencing — Several other fencing methods that disable I/O or power of an inoperable node, including IBM Bladecenters, PAP, DRAC/MC, HP ILO, IPMI, IBM RSA II,
and others
Figure 1-4 shows an example of power fencing. In the example, the fencing program in
node A causes the power controller to power off node D. Figure 1-5 shows an example of
Fibre Channel switch fencing. In the example, the fencing program in node A causes the
Fibre Channel switch to disable the port for node D, disconnecting node D from storage.
8
Chapter 1. Red Hat Cluster Suite Overview
Figure 1-4. Power Fencing Example
Figure 1-5. Fibre Channel Switch Fencing Example
Chapter 1. Red Hat Cluster Suite Overview
9
Specifying a fencing method consists of editing a cluster configuration file to assign a
fencing-method name, the fencing agent, and the fencing device for each node in the cluster.
Note
Other fencing parameters may be necessary depending on the type of cluster manager
(either CMAN or GULM) selected in a cluster.
The way in which a fencing method is specified depends on if a node has either dual power
supplies or multiple paths to storage. If a node has dual power supplies, then the fencing
method for the node must specify at least two fencing devices — one fencing device for
each power supply (refer to Figure 1-6). Similarly, if a node has multiple paths to Fibre
Channel storage, then the fencing method for the node must specify one fencing device for
each path to Fibre Channel storage. For example, if a node has two paths to Fibre Channel
storage, the fencing method should specify two fencing devices — one for each path to
Fibre Channel storage (refer to Figure 1-7).
Figure 1-6. Fencing a Node with Dual Power Supplies
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Chapter 1. Red Hat Cluster Suite Overview
Figure 1-7. Fencing a Node with Dual Fibre Channel Connections
You can configure a node with one fencing method or multiple fencing methods. When
you configure a node for one fencing method, that is the only fencing method available for
fencing that node. When you configure a node for multiple fencing methods, the fencing
methods are cascaded from one fencing method to another according to the order of the
fencing methods specified in the cluster configuration file. If a node fails, it is fenced using
the first fencing method specified in the cluster configuration file for that node. If the first
fencing method is not successful, the next fencing method specified for that node is used.
If none of the fencing methods is successful, then fencing starts again with the first fencing
method specified, and continues looping through the fencing methods in the order specified
in the cluster configuration file until the node has been fenced.
1.3.4. Cluster Configuration System
The Cluster Configuration System (CCS) manages the cluster configuration and provides
configuration information to other cluster components in a Red Hat cluster. CCS runs in
each cluster node and makes sure that the cluster configuration file in each cluster node is
up to date. For example, if a cluster system administrator updates the configuration file in
Node A, CCS propagates the update from Node A to the other nodes in the cluster (refer
to Figure 1-8).
Chapter 1. Red Hat Cluster Suite Overview
11
Figure 1-8. CCS Overview
Other cluster components (for example, CMAN) access configuration information from
the configuration file through CCS (refer to Figure 1-8).
Figure 1-9. Accessing Configuration Information
12
Chapter 1. Red Hat Cluster Suite Overview
The cluster configuration file (/etc/cluster/cluster.conf) is an XML file that describes the following cluster characteristics:
•
Cluster name — Displays the cluster name, cluster configuration file revision level, locking type (either DLM or GULM), and basic fence timing properties used when a node
joins a cluster or is fenced from the cluster.
•
Cluster — Displays each node of the cluster, specifying node name, number of quorum
votes, and fencing method for that node.
•
Fence Device — Displays fence devices in the cluster. Parameters vary according to the
type of fence device. For example for a power controller used as a fence device, the
cluster configuration defines the name of the power controller, its IP address, login, and
password.
•
Managed Resources — Displays resources required to create cluster services. Managed
resources includes the definition of failover domains, resources (for example an IP address), and services. Together the managed resources define cluster services and failover
behavior of the cluster services.
1.4. High-availability Service Management
High-availability service management provides the ability to create and manage highavailability cluster services in a Red Hat cluster. The key component for high-availability
service management in a Red Hat cluster, rgmanager, implements cold failover for offthe-shelf applications. In a Red Hat cluster, an application is configured with other cluster
resources to form a high-availability cluster service. A high-availability cluster service can
fail over from one cluster node to another with no apparent interruption to cluster clients.
Cluster-service failover can occur if a cluster node fails or if a cluster system administrator
moves the service from one cluster node to another (for example, for a planned outage of
a cluster node).
To create a high-availability service, you must configure it in the cluster configuration file.
A cluster service comprises cluster resources. Cluster resources are building blocks that
you create and manage in the cluster configuration file — for example, an IP address, an
application initialization script, or a Red Hat GFS shared partition.
You can associate a cluster service with a failover domain. A failover domain is a subset
of cluster nodes that are eligible to run a particular cluster service (refer to Figure 1-10).
A cluster service can run on only one cluster node at a time to maintain data integrity. You
can specify failover priority in a failover domain. Specifying failover priority consists of
assigning a priority level to each node in a failover domain. The priority level determines
the failover order — determining which node that a cluster service should fail over to.
If you do not specify failover priority, a cluster service can fail over to any node in its
failover domain. Also, you can specify if a cluster service is restricted to run only on nodes
of its associated failover domain. (When associated with an unrestricted failover domain, a
Chapter 1. Red Hat Cluster Suite Overview
13
cluster service can start on any cluster node in the event no member of the failover domain
is available.)
In Figure 1-10, Failover Domain 1 is configured to restrict failover within that domain;
therefore, Cluster Service X can only fail over between Node A and Node B. Failover Domain 2 is also configured to restrict failover with its domain; additionally, it is configured
for failover priority. Failover Domain 2 priority is configured with Node C as priority 1,
Node B as priority 2, and Node D as priority 3. If Node C fails, Cluster Service Y fails over
to Node B next. If it cannot fail over to Node B, it tries failing over to Node D. Failover
Domain 3 is configured with no priority and no restrictions. If the node that Cluster Service
Z is running on fails, Cluster Service Z tries failing over to one of the nodes in Failover
Domain 3. However, if none of those nodes is available, Cluster Service Z can fail over to
any node in the cluster.
Figure 1-10. Failover Domains
14
Chapter 1. Red Hat Cluster Suite Overview
Figure 1-11 shows an example of a high-availability cluster service that is a web server
named "content-webserver". It is running in cluster node B and is in a failover domain that
consists of nodes A, B, and D. In addition, the failover domain is configured with a failover
priority to fail over to node D before node A and to restrict failover to nodes only in that
failover domain. The cluster service comprises these cluster resources:
•
IP address resource — IP address 10.10.10.201
•
An application resource named "httpd-content" — a web server application init script
/etc/init.d/httpd (specifying httpd)
•
A file system resource — Red Hat GFS named "gfs-content-webserver"
Figure 1-11. Web Server Cluster Service Example
Clients access the cluster service through the IP address 10.10.10.201, enabling interaction
with the web server application, httpd-content. The httpd-content application uses the gfscontent-webserver file system. If node B were to fail, the content-webserver cluster service
would fail over to node D. If node D were not available or also failed, the service would fail
over to node A. Failover would occur with no apparent interruption to the cluster clients.
The cluster service would be accessible from another cluster node via the same IP address
as it was before failover.
Chapter 1. Red Hat Cluster Suite Overview
15
1.5. Red Hat GFS
Red Hat GFS is a cluster file system that allows a cluster of nodes to simultaneously access
a block device that is shared among the nodes. GFS is a native file system that interfaces
directly with the VFS layer of the Linux kernel file-system interface. GFS employs distributed metadata and multiple journals for optimal operation in a cluster. To maintain file
system integrity, GFS uses a lock manager to coordinate I/O. When one node changes data
on a GFS file system, that change is immediately visible to the other cluster nodes using
that file system.
Using Red Hat GFS, you can achieve maximum application uptime through the following
benefits:
•
Simplifying your data infrastructure
•
•
•
Install and patch applications once for the entire cluster.
•
Eliminates the need for redundant copies of application data (duplication).
•
Enables concurrent read/write access to data by many clients.
•
Simplifies backup and disaster recovery (only one file system to back up or recover).
Maximize the use of storage resources; minimize storage administration costs.
•
Manage storage as a whole instead of by partition.
•
Decrease overall storage needs by eliminating the need for data replications.
Scale the cluster seamlessly by adding servers or storage on the fly.
•
No more partitioning storage through complicated techniques.
•
Add servers to the cluster on the fly by mounting them to the common file system.
Nodes that run Red Hat GFS are configured and managed with Red Hat Cluster Suite configuration and management tools. Volume management is managed through CLVM (Cluster Logical Volume Manager). Red Hat GFS provides data sharing among GFS nodes in
a Red Hat cluster. GFS provides a single, consistent view of the file-system name space
across the GFS nodes in a Red Hat cluster. GFS allows applications to install and run without much knowledge of the underlying storage infrastructure. Also, GFS provides features
that are typically required in enterprise environments, such as quotas, multiple journals,
and multipath support.
GFS provides a versatile method of networking storage according to the performance, scalability, and economic needs of your storage environment. This chapter provides some very
basic, abbreviated information as background to help you understand GFS.
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Chapter 1. Red Hat Cluster Suite Overview
You can deploy GFS in a variety of configurations to suit your needs for performance,
scalability, and economy. For superior performance and scalability, you can deploy GFS in
a cluster that is connected directly to a SAN. For more economical needs, you can deploy
GFS in a cluster that is connected to a LAN with servers that use GNBD (Global Network
Block Device) or to iSCSI (Internet Small Computer System Interface) devices. (For more
information about GNBD, refer to Section 1.7 Global Network Block Device.)
The following sections provide examples of how GFS can be deployed to suit your needs
for performance, scalability, and economy:
•
Section 1.5.1 Superior Performance and Scalability
•
Section 1.5.2 Performance, Scalability, Moderate Price
•
Section 1.5.3 Economy and Performance
Note
The GFS deployment examples reflect basic configurations; your needs might require a
combination of configurations shown in the examples.
1.5.1. Superior Performance and Scalability
You can obtain the highest shared-file performance when applications access storage directly. The GFS SAN configuration in Figure 1-12 provides superior file performance for
shared files and file systems. Linux applications run directly on cluster nodes using GFS.
Without file protocols or storage servers to slow data access, performance is similar to individual Linux servers with directly connected storage; yet, each GFS application node has
equal access to all data files. GFS supports over 300 GFS nodes.
Chapter 1. Red Hat Cluster Suite Overview
17
Figure 1-12. GFS with a SAN
1.5.2. Performance, Scalability, Moderate Price
Multiple Linux client applications on a LAN can share the same SAN-based data as shown
in Figure 1-13. SAN block storage is presented to network clients as block storage devices
by GNBD servers. From the perspective of a client application, storage is accessed as if
it were directly attached to the server in which the application is running. Stored data is
actually on the SAN. Storage devices and data can be equally shared by network client
applications. File locking and sharing functions are handled by GFS for each network
client.
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Chapter 1. Red Hat Cluster Suite Overview
Figure 1-13. GFS and GNBD with a SAN
1.5.3. Economy and Performance
Figure 1-14 shows how Linux client applications can take advantage of an existing Ethernet
topology to gain shared access to all block storage devices. Client data files and file systems
can be shared with GFS on each client. Application failover can be fully automated with
Red Hat Cluster Suite.
Chapter 1. Red Hat Cluster Suite Overview
19
Figure 1-14. GFS and GNBD with Directly Connected Storage
1.6. Cluster Logical Volume Manager
The Cluster Logical Volume Manager (CLVM) provides a cluster-wide version of LVM2.
CLVM provides the same capabilities as LVM2 on a single node, but makes the volumes
available to all nodes in a Red Hat cluster. The logical volumes created with CLVM make
logical volumes available to all nodes in a cluster.
The key component in CLVM is clvmd. clvmd is a daemon that provides clustering extensions to the standard LVM2 tool set and allows LVM2 commands to manage shared
storage. clvmd runs in each cluster node and distributes LVM metadata updates in a cluster, thereby presenting each cluster node with the same view of the logical volumes (refer
to Figure 1-15). Logical volumes created with CLVM on shared storage are visible to all
nodes that have access to the shared storage. CLVM allows a user to configure logical volumes on shared storage by locking access to physical storage while a logical volume is
being configured. CLVM uses the lock-management service provided by the cluster infrastructure (refer to Section 1.3 Cluster Infrastructure).
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Chapter 1. Red Hat Cluster Suite Overview
Note
Using CLVM requires minor changes to /etc/lvm/lvm.conf for cluster-wide locking.
Figure 1-15. CLVM Overview
You can configure CLVM using the same commands as LVM2 or by using the LVM graphical user interface (refer to Figure 1-16). Figure 1-17 shows the basic concept of creating
logical volumes from Linux partitions and shows the commands used to create logical
volumes.
Chapter 1. Red Hat Cluster Suite Overview
Figure 1-16. LVM Graphical User Interface
Figure 1-17. Creating Logical Volumes
21
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Chapter 1. Red Hat Cluster Suite Overview
1.7. Global Network Block Device
Global Network Block Device (GNBD) provides block-device access to Red Hat GFS over
TCP/IP. GNBD is similar in concept to NBD; however, GNBD is GFS-specific and tuned
solely for use with GFS. GNBD is useful when the need for more robust technologies —
Fibre Channel or single-initiator SCSI — are not necessary or are cost-prohibitive.
GNBD consists of two major components: a GNBD client and a GNBD server. A GNBD
client runs in a node with GFS and imports a block device exported by a GNBD server. A
GNBD server runs in another node and exports block-level storage from its local storage
(either directly attached storage or SAN storage). Refer to Figure 1-18. Multiple GNBD
clients can access a device exported by a GNBD server, thus making a GNBD suitable for
use by a group of nodes running GFS.
Figure 1-18. GNBD Overview
1.8. Linux Virtual Server
Linux Virtual Server (LVS) is a set of integrated software components for balancing the IP
load across a set of real servers. LVS runs on a pair of equally configured computers: one
that is an active LVS router and one that is a backup LVS router. The active LVS router
serves two roles:
Chapter 1. Red Hat Cluster Suite Overview
•
To balance the load across the real servers.
•
To check the integrity of the services on each real server.
23
The backup LVS router monitors the active LVS router and takes over from it in case the
active LVS router fails.
Figure 1-19 provides an overview of the LVS components and their interrelationship.
Figure 1-19. Components of a Running LVS Cluster
The pulse daemon runs on both the active and passive LVS routers. On the backup LVS
router, pulse sends a heartbeat to the public interface of the active router to make sure the
active LVS router is properly functioning. On the active LVS router, pulse starts the lvs
daemon and responds to heartbeat queries from the backup LVS router.
Once started, the lvs daemon calls the ipvsadm utility to configure and maintain the
IPVS (IP Virtual Server) routing table in the kernel and starts a nanny process for each
configured virtual server on each real server. Each nanny process checks the state of one
configured service on one real server, and tells the lvs daemon if the service on that real
server is malfunctioning. If a malfunction is detected, the lvs daemon instructs ipvsadm
to remove that real server from the IPVS routing table.
If the backup LVS router does not receive a response from the active LVS router, it initiates
failover by calling send_arp to reassign all virtual IP addresses to the NIC hardware
addresses (MAC address) of the backup LVS router, sends a command to the active LVS
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Chapter 1. Red Hat Cluster Suite Overview
router via both the public and private network interfaces to shut down the lvs daemon
on the active LVS router, and starts the lvs daemon on the backup LVS router to accept
requests for the configured virtual servers.
To an outside user accessing a hosted service (such as a website or database application),
LVS appears as one server. However, the user is actually accessing real servers behind the
LVS routers.
Because there is no built-in component in LVS to share the data among real servers, you
have have two basic options:
•
Synchronize the data across the real servers.
•
Add a third layer to the topology for shared data access.
The first option is preferred for servers that do not allow large numbers of users to upload
or change data on the real servers. If the real servers allow large numbers of users to modify
data, such as an e-commerce website, adding a third layer is preferable.
There are many ways to synchronize data among real servers. For example, you can use
shell scripts to post updated web pages to the real servers simultaneously. Also, you can use
programs such as rsync to replicate changed data across all nodes at a set interval. However, in environments where users frequently upload files or issue database transactions,
using scripts or the rsync command for data synchronization does not function optimally.
Therefore, for real servers with a high amount of uploads, database transactions, or similar
traffic, a three-tiered topology is more appropriate for data synchronization.
1.8.1. Two-Tier LVS Topology
Figure 1-20 shows a simple LVS configuration consisting of two tiers: LVS routers and
real servers. The LVS-router tier consists of one active LVS router and one backup LVS
router. The real-server tier consists of real servers connected to the private network. Each
LVS router has two network interfaces: one connected to a public network (Internet) and
one connected to a private network. A network interface connected to each network allows the LVS routers to regulate traffic between clients on the public network and the real
servers on the private network. In Figure 1-20, the active LVS router uses Network Address
Translation (NAT) to direct traffic from the public network to real servers on the private
network, which in turn provide services as requested. The real servers pass all public traffic
through the active LVS router. From the perspective of clients on the public network, the
LVS router appears as one entity.
Chapter 1. Red Hat Cluster Suite Overview
25
Figure 1-20. Two-Tier LVS Topology
Service requests arriving at an LVS router are addressed to a virtual IP address or VIP.
This is a publicly-routable address that the administrator of the site associates with a fullyqualified domain name, such as www.example.com, and which is assigned to one or more
virtual servers1. Note that a VIP address migrates from one LVS router to the other during a
failover, thus maintaining a presence at that IP address, also known as floating IP addresses.
VIP addresses may be aliased to the same device that connects the LVS router to the public
network. For instance, if eth0 is connected to the Internet, then multiple virtual servers can
be aliased to eth0:1. Alternatively, each virtual server can be associated with a separate
device per service. For example, HTTP traffic can be handled on eth0:1, and FTP traffic
can be handled on eth0:2.
Only one LVS router is active at a time. The role of the active LVS router is to redirect
service requests from virtual IP addresses to the real servers. The redirection is based on
one of eight load-balancing algorithms:
•
1.
Round-Robin Scheduling — Distributes each request sequentially around a pool of real
servers. Using this algorithm, all the real servers are treated as equals without regard to
capacity or load.
A virtual server is a service configured to listen on a specific virtual IP.
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Chapter 1. Red Hat Cluster Suite Overview
•
Weighted Round-Robin Scheduling — Distributes each request sequentially around a
pool of real servers but gives more jobs to servers with greater capacity. Capacity is indicated by a user-assigned weight factor, which is then adjusted up or down by dynamic
load information. This is a preferred choice if there are significant differences in the capacity of real servers in a server pool. However, if the request load varies dramatically,
a more heavily weighted server may answer more than its share of requests.
•
Least-Connection — Distributes more requests to real servers with fewer active connections. This is a type of dynamic scheduling algorithm, making it a better choice if there
is a high degree of variation in the request load. It is best suited for a real server pool
where each server node has roughly the same capacity. If the real servers have varying
capabilities, weighted least-connection scheduling is a better choice.
•
Weighted Least-Connections (default) — Distributes more requests to servers with fewer
active connections relative to their capacities. Capacity is indicated by a user-assigned
weight, which is then adjusted up or down by dynamic load information. The addition
of weighting makes this algorithm ideal when the real server pool contains hardware of
varying capacity.
•
Locality-Based Least-Connection Scheduling — Distributes more requests to servers
with fewer active connections relative to their destination IPs. This algorithm is for use
in a proxy-cache server cluster. It routes the packets for an IP address to the server for
that address unless that server is above its capacity and has a server in its half load, in
which case it assigns the IP address to the least loaded real server.
•
Locality-Based Least-Connection Scheduling with Replication Scheduling —
Distributes more requests to servers with fewer active connections relative to their
destination IPs. This algorithm is also for use in a proxy-cache server cluster. It differs
from Locality-Based Least-Connection Scheduling by mapping the target IP address to
a subset of real server nodes. Requests are then routed to the server in this subset with
the lowest number of connections. If all the nodes for the destination IP are above
capacity, it replicates a new server for that destination IP address by adding the real
server with the least connections from the overall pool of real servers to the subset of
real servers for that destination IP. The most-loaded node is then dropped from the real
server subset to prevent over-replication.
•
Source Hash Scheduling — Distributes requests to the pool of real servers by looking
up the source IP in a static hash table. This algorithm is for LVS routers with multiple
firewalls.
Also, the active LVS router dynamically monitors the overall health of the specific services
on the real servers through simple send/expect scripts. To aid in detecting the health of
services that require dynamic data, such as HTTPS or SSL, you can also call external
executables. If a service on a real server malfunctions, the active LVS router stops sending
jobs to that server until it returns to normal operation.
The backup LVS router performs the role of a standby system. Periodically, the LVS
routers exchange heartbeat messages through the primary external public interface and,
in a failover situation, the private interface. Should the backup LVS router fail to receive a
heartbeat message within an expected interval, it initiates a failover and assumes the role
Chapter 1. Red Hat Cluster Suite Overview
27
of the active LVS router. During failover, the backup LVS router takes over the VIP addresses serviced by the failed router using a technique known as ARP spoofing — where
the backup LVS router announces itself as the destination for IP packets addressed to the
failed node. When the failed node returns to active service, the backup LVS router assumes
its backup role again.
The simple, two-tier configuration in Figure 1-20 is suited best for clusters serving data
that does not change very frequently — such as static web pages — because the individual
real servers do not automatically synchronize data among themselves.
1.8.2. Three-Tier LVS Topology
Figure 1-21 shows a typical three-tier LVS configuration. In the example, the active LVS
router routes the requests from the public network (Internet) to the second tier — real
servers. Each real server then accesses a shared data source of a Red Hat cluster in the
third tier over the private network.
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Chapter 1. Red Hat Cluster Suite Overview
Figure 1-21. Three-Tier LVS Topology
This topology is suited well for busy FTP servers, where accessible data is stored on a central, highly available server and accessed by each real server via an exported NFS directory or Samba share. This topology is also recommended for websites that access a central,
high-availability database for transactions. Additionally, using an active-active configuration with a Red Hat cluster, you can configure one high-availability cluster to serve both of
these roles simultaneously.
Chapter 1. Red Hat Cluster Suite Overview
29
1.8.3. Routing Methods
You can use Network Address Translation (NAT) routing or direct routing with LVS. The
following sections briefly describe NAT routing and direct routing with LVS.
1.8.3.1. NAT Routing
Figure 1-22, illustrates LVS using NAT routing to move requests between the Internet and
a private network.
Figure 1-22. LVS Implemented with NAT Routing
In the example, there are two NICs in the active LVS router. The NIC for the Internet has
a real IP address on eth0 and has a floating IP address aliased to eth0:1. The NIC for
the private network interface has a real IP address on eth1 and has a floating IP address
aliased to eth1:1. In the event of failover, the virtual interface facing the Internet and the
private facing virtual interface are taken over by the backup LVS router simultaneously.
All the real servers on the private network use the floating IP for the NAT router as their
default route to communicate with the active LVS router so that their abilities to respond
to requests from the Internet is not impaired.
In the example, the LVS router’s public LVS floating IP address and private NAT floating
IP address are aliased to two physical NICs. While it is possible to associate each floating
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Chapter 1. Red Hat Cluster Suite Overview
IP address to its physical device on the LVS router nodes, having more than two NICs is
not a requirement.
Using this topology, the active LVS router receives the request and routes it to the appropriate server. The real server then processes the request and returns the packets to the
LVS router. The LVS router uses network address translation to replace the address of the
real server in the packets with the LVS routers public VIP address. This process is called
IP masquerading because the actual IP addresses of the real servers is hidden from the
requesting clients.
Using NAT routing, the real servers can be any kind of computers running a variety operating systems. The main disadvantage of NAT routing is that the LVS router may become a
bottleneck in large deployments because it must process outgoing and incoming requests.
1.8.3.2. Direct Routing
Direct routing provides increased performance benefits compared to NAT routing. Direct
routing allows the real servers to process and route packets directly to a requesting user
rather than passing outgoing packets through the LVS router. Direct routing reduces the
possibility of network performance issues by relegating the job of the LVS router to processing incoming packets only.
Chapter 1. Red Hat Cluster Suite Overview
31
Figure 1-23. LVS Implemented with Direct Routing
In a typical direct-routing LVS configuration, an LVS router receives incoming server requests through a virtual IP (VIP) and uses a scheduling algorithm to route the request to
real servers. Each real server processes requests and sends responses directly to clients,
bypassing the LVS routers. Direct routing allows for scalability in that real servers can be
added without the added burden on the LVS router to route outgoing packets from the real
server to the client, which can become a bottleneck under heavy network load.
While there are many advantages to using direct routing in LVS, there are limitations.
The most common issue with direct routing and LVS is with Address Resolution Protocol
(ARP).
In typical situations, a client on the Internet sends a request to an IP address. Network
routers typically send requests to their destination by relating IP addresses to a machine’s
MAC address with ARP. ARP requests are broadcast to all connected machines on a network, and the machine with the correct IP/MAC address combination receives the packet.
The IP/MAC associations are stored in an ARP cache, which is cleared periodically (usually every 15 minutes) and refilled with IP/MAC associations.
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The issue with ARP requests in a direct-routing LVS configuration is that because a client
request to an IP address must be associated with a MAC address for the request to be handled, the virtual IP address of the LVS router must also be associated to a MAC. However,
because both the LVS router and the real servers have the same VIP, the ARP request is
broadcast to all the nodes associated with the VIP. This can cause several problems, such as
the VIP being associated directly to one of the real servers and processing requests directly,
bypassing the LVS router completely and defeating the purpose of the LVS configuration.
Using an LVS router with a powerful CPU that can respond quickly to client requests does
not necessarily remedy this issue. If the LVS router is under heavy load, it may respond
to the ARP request more slowly than an underutilized real server, which responds more
quickly and is assigned the VIP in the ARP cache of the requesting client.
To solve this issue, the incoming requests should only associate the VIP to the LVS router,
which will properly process the requests and send them to the real server pool. This can be
done by using the arptables packet-filtering tool.
1.8.4. Persistence and Firewall Marks
In certain situations, it may be desirable for a client to reconnect repeatedly to the same
real server, rather than have an LVS load-balancing algorithm send that request to the best
available server. Examples of such situations include multi-screen web forms, cookies,
SSL, and FTP connections. In those cases, a client may not work properly unless the transactions are being handled by the same server to retain context. LVS provides two different
features to handle this: persistence and firewall marks.
1.8.4.1. Persistence
When enabled, persistence acts like a timer. When a client connects to a service, LVS
remembers the last connection for a specified period of time. If that same client IP address
connects again within that period, it is sent to the same server it connected to previously
— bypassing the load-balancing mechanisms. When a connection occurs outside the time
window, it is handled according to the scheduling rules in place.
Persistence also allows you to specify a subnet mask to apply to the client IP address test as
a tool for controlling what addresses have a higher level of persistence, thereby grouping
connections to that subnet.
Grouping connections destined for different ports can be important for protocols that use
more than one port to communicate, such as FTP. However, persistence is not the most efficient way to deal with the problem of grouping together connections destined for different
ports. For these situations, it is best to use firewall marks.
Chapter 1. Red Hat Cluster Suite Overview
33
1.8.4.2. Firewall Marks
Firewall marks are an easy and efficient way to a group ports used for a protocol or group
of related protocols. For example, if LVS is deployed to run an e-commerce site, firewall
marks can be used to bundle HTTP connections on port 80 and secure, HTTPS connections
on port 443. By assigning the same firewall mark to the virtual server for each protocol,
state information for the transaction can be preserved because the LVS router forwards all
requests to the same real server after a connection is opened.
Because of its efficiency and ease-of-use, administrators of LVS should use firewall marks
instead of persistence whenever possible for grouping connections. However, you should
still add persistence to the virtual servers in conjunction with firewall marks to ensure the
clients are reconnected to the same server for an adequate period of time.
1.9. Cluster Administration GUI
This section provides an overview of the cluster administration graphical user interface
(GUI) available with Red Hat Cluster Suite — system-config-cluster.
The GUI is for use with the cluster infrastructure and the high-availability
service management components (refer to Section 1.3 Cluster Infrastructure and
Section 1.4 High-availability Service Management). The GUI consists of two major
functions: the Cluster Configuration Tool and the Cluster Status Tool. The Cluster
Configuration Tool provides the capability to create, edit, and propagate the cluster
configuration file (/etc/cluster/cluster.conf). The Cluster Status Tool provides
the capability to manage high-availability services. The following sections summarize
those functions.
•
Section 1.9.1 Cluster Configuration Tool
•
Section 1.9.2 Cluster Status Tool
In addition to the Cluster Administration GUI, command line tools are available for administering the cluster infrastructure and the high-availability service management components. The command line tools are used by the Cluster Administration GUI and init
scripts supplied by Red Hat. Table 1-1 summarizes the command line tools.
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Chapter 1. Red Hat Cluster Suite Overview
Command
Line Tool
Used With
Purpose
ccs_tool —
Cluster
Infrastructure
ccs_tool is a program for making online updates
to the cluster configuration file. It provides the
capability to create and modify cluster
infrastructure components (for example, creating a
cluster, adding and removing a node). For more
information about this tool, refer to the ccs_tool(8)
man page.
cman_tool —
Cluster
Infrastructure
cman_tool is a program that manages the CMAN
fence_tool
Cluster
Infrastructure
fence_tool is a program used to join or leave the
clustat —
Highavailability
Service
Management
Components
The clustat command displays the status of the
cluster. It shows membership information, quorum
view, and the state of all configured user services.
For more information about this tool, refer to the
clustat(8) man page.
clusvcadm —
Highavailability
Service
Management
Components
The clusvcadm command allows you to enable,
disable, relocate, and restart high-availability
services in a cluster. For more information about
this tool, refer to the clusvcadm(8) man page.
Cluster
Configuration
System Tool
Cluster
Management
Tool
— Fence Tool
Cluster Status
Utility
Cluster User
Service
Administration
Utility
Table 1-1. Command Line Tools
cluster manager. It provides the capability to join a
cluster, leave a cluster, kill a node, or change the
expected quorum votes of a node in a cluster. For
more information about this tool, refer to the
cman_tool(8) man page.
default fence domain. Specifically, it starts the fence
daemon (fenced) to join the domain and kills
fenced to leave the domain. For more information
about this tool, refer to the fence_tool(8) man page.
Chapter 1. Red Hat Cluster Suite Overview
35
1.9.1. Cluster Configuration Tool
You can access the Cluster Configuration Tool (Figure 1-24) through the Cluster Configuration tab in the Cluster Administration GUI.
Figure 1-24. Cluster Configuration Tool
The Cluster Configuration Tool represents cluster configuration components in the configuration file (/etc/cluster/cluster.conf) with a hierarchical graphical display in
the left panel. A triangle icon to the left of a component name indicates that the component
has one or more subordinate components assigned to it. Clicking the triangle icon expands
and collapses the portion of the tree below a component. The components displayed in the
GUI are summarized as follows:
•
Cluster Nodes — Displays cluster nodes. Nodes are represented by name as subordinate
elements under Cluster Nodes. Using configuration buttons at the bottom of the right
frame (below Properties), you can add nodes, delete nodes, edit node properties, and
configure fencing methods for each node.
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Chapter 1. Red Hat Cluster Suite Overview
•
Fence Devices — Displays fence devices. Fence devices are represented as subordinate
elements under Fence Devices. Using configuration buttons at the bottom of the right
frame (below Properties), you can add fence devices, delete fence devices, and edit
fence-device properties. Fence devices must be defined before you can configure fencing
(with the Manage Fencing For This Node button) for each node.
•
Managed Resources — Displays failover domains, resources, and services.
•
•
Failover Domains — For configuring one or more subsets of cluster nodes used to
run a high-availability service in the event of a node failure. Failover domains are represented as subordinate elements under Failover Domains. Using configuration buttons at the bottom of the right frame (below Properties), you can create failover domains (when Failover Domains is selected) or edit failover domain properties (when
a failover domain is selected).
Resources — For configuring shared resources to be used by high-availability services. Shared resources consist of file systems, IP addresses, NFS mounts and exports, and user-created scripts that are available to any high-availability service in the
cluster. Resources are represented as subordinate elements under Resources. Using
configuration buttons at the bottom of the right frame (below Properties), you can
create resources (when Resources is selected) or edit resource properties (when a
resource is selected).
Note
The Cluster Configuration Tool provides the capability to configure private resources, also. A private resource is a resource that is configured for use with only
one service. You can configure a private resource within a Service component in
the GUI.
•
Services — For creating and configuring high-availability services. A service is configured by assigning resources (shared or private), assigning a failover domain, and
defining a recovery policy for the service. Services are represented as subordinate elements under Services. Using configuration buttons at the bottom of the right frame
(below Properties), you can create services (when Services is selected) or edit service
properties (when a service is selected).
Figure 1-25 shows an example of the hierarchical relationship among cluster nodes, highavailability services, and resources. The cluster nodes are connected to one or more fencing
devices. Nodes can be grouped into a failover domain for a cluster service. The services
comprise resources such as NFS exports, IP addresses, and shared GFS partitions.
Chapter 1. Red Hat Cluster Suite Overview
Figure 1-25. Cluster Configuration Structure
37
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1.9.2. Cluster Status Tool
You can access the Cluster Status Tool (Figure 1-26) through the Cluster Management
tab in Cluster Administration GUI.
Figure 1-26. Cluster Status Tool
The nodes and services displayed in the Cluster Status Tool are determined by the cluster
configuration file (/etc/cluster/cluster.conf). You can use the Cluster Status Tool
to enable, disable, restart, or relocate a high-availability service. The Cluster Status Tool
displays the current cluster status in the Services area and automatically updates the status
every 10 seconds.
To enable a service, you can select the service in the Services area and click Enable. To
disable a service, you can select the service in the Services area and click Disable. To
restart a service, you can select the service in the Services area and click Restart. To
relocate a service from one node to another, you can drag the service to another node
and drop the service onto that node. Relocating a node restarts the service on that node.
Chapter 1. Red Hat Cluster Suite Overview
39
(Relocating a service to its current node — that is, dragging a service to its current node
and dropping the service onto that node — restarts the service.)
The following tables describe the members and services status information displayed by
the Cluster Status Tool.
Members Status
Description
Member
The node is part of the cluster.
Note: A node can be a member of a cluster; however, the node
may be inactive and incapable of running services. For example,
if rgmanager is not running on the node, but all other cluster
software components are running in the node, the node appears as
a Member in the Cluster Status Tool.
Dead
The node is unable to participate as a cluster member. The most
basic cluster software is not running on the node.
Table 1-2. Members Status
Services Status
Description
Started
The service resources are configured and available on the cluster
system that owns the service.
Pending
The service has failed on a member and is pending start on
another member.
Disabled
The service has been disabled, and does not have an assigned
owner. A disabled service is never restarted automatically by the
cluster.
Stopped
The service is not running; it is waiting for a member capable of
starting the service. A service remains in the stopped state if
autostart is disabled.
Failed
The service has failed to start on the cluster and cannot
successfully stop the service. A failed service is never restarted
automatically by the cluster.
Table 1-3. Services Status
40
Chapter 1. Red Hat Cluster Suite Overview
1.10. Linux Virtual Server Administration GUI
This section provides an overview of the LVS configuration tool available with Red Hat
Cluster Suite — the Piranha Configuration Tool. The Piranha Configuration Tool is a
Web-browser graphical user interface (GUI) that provides a structured approach to creating
the configuration file for LVS — /etc/sysconfig/ha/lvs.cf.
To access the Piranha Configuration Tool you need the piranha-gui service
running on the active LVS router. You can access the Piranha Configuration Tool
locally or remotely with a Web browser. You can access it locally with this URL:
http://localhost:3636. You can access it remotely with either the hostname or
the real IP address followed by :3636. If you are accessing the Piranha Configuration
Tool remotely, you need an ssh connection to the active LVS router as the root user.
Starting the Piranha Configuration Tool causes the Piranha Configuration Tool welcome page to be displayed (refer to Figure 1-27). Logging in to the welcome page provides access to the four main screens or panels: CONTROL/MONITORING, GLOBAL
SETTINGS, REDUNDANCY, and VIRTUAL SERVERS. In addition, the VIRTUAL
SERVERS panel contains four subsections. The CONTROL/MONITORING panel is
the first panel displayed after you log in at the welcome screen.
Figure 1-27. The Welcome Panel
The following sections provide a brief description of the Piranha Configuration Tool
configuration pages.
1.10.1. CONTROL/MONITORING
The CONTROL/MONITORING Panel displays runtime status. It displays the status of
the pulse daemon, the LVS routing table, and the LVS-spawned nanny processes.
Chapter 1. Red Hat Cluster Suite Overview
41
Figure 1-28. The CONTROL/MONITORING Panel
Auto update
Enables the status display to be updated automatically at a user-configurable interval
set in the Update frequency in seconds text box (the default value is 10 seconds).
It is not recommended that you set the automatic update to an interval less than 10
seconds. Doing so may make it difficult to reconfigure the Auto update interval because the page will update too frequently. If you encounter this issue, simply click on
another panel and then back on CONTROL/MONITORING.
Update information now
Provides manual update of the status information.
CHANGE PASSWORD
Clicking this button takes you to a help screen with information on how to change the
administrative password for the Piranha Configuration Tool.
1.10.2. GLOBAL SETTINGS
The GLOBAL SETTINGS panel is where the LVS administrator defines the networking
details for the primary LVS router’s public and private network interfaces.
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Chapter 1. Red Hat Cluster Suite Overview
Figure 1-29. The GLOBAL SETTINGS Panel
The top half of this panel sets up the primary LVS router’s public and private network
interfaces.
Primary server public IP
The publicly routable real IP address for the primary LVS node.
Primary server private IP
The real IP address for an alternative network interface on the primary LVS node.
This address is used solely as an alternative heartbeat channel for the backup router.
Use network type
Selects select NAT routing.
The next three fields are specifically for the NAT router’s virtual network interface connected the private network with the real servers.
NAT Router IP
The private floating IP in this text field. This floating IP should be used as the gateway
for the real servers.
Chapter 1. Red Hat Cluster Suite Overview
43
NAT Router netmask
If the NAT router’s floating IP needs a particular netmask, select it from drop-down
list.
NAT Router device
Defines the device name of the network interface for the floating IP address, such as
eth1:1.
1.10.3. REDUNDANCY
The REDUNDANCY panel allows you to configure of the backup LVS router node and
set various heartbeat monitoring options.
Figure 1-30. The REDUNDANCY Panel
Redundant server public IP
The public real IP address for the backup LVS router.
44
Chapter 1. Red Hat Cluster Suite Overview
Redundant server private IP
The backup router’s private real IP address.
The rest of the panel is for configuring the heartbeat channel, which is used by the backup
node to monitor the primary node for failure.
Heartbeat Interval (seconds)
Sets the number of seconds between heartbeats — the interval that the backup node
will check the functional status of the primary LVS node.
Assume dead after (seconds)
If the primary LVS node does not respond after this number of seconds, then the
backup LVS router node will initiate failover.
Heartbeat runs on port
Sets the port at which the heartbeat communicates with the primary LVS node. The
default is set to 539 if this field is left blank.
1.10.4. VIRTUAL SERVERS
The VIRTUAL SERVERS panel displays information for each currently defined virtual
server. Each table entry shows the status of the virtual server, the server name, the virtual
IP assigned to the server, the netmask of the virtual IP, the port number to which the service
communicates, the protocol used, and the virtual device interface.
Chapter 1. Red Hat Cluster Suite Overview
45
Figure 1-31. The VIRTUAL SERVERS Panel
Each server displayed in the VIRTUAL SERVERS panel can be configured on subsequent
screens or subsections.
To add a service, click the ADD button. To remove a service, select it by clicking the radio
button next to the virtual server and click the DELETE button.
To enable or disable a virtual server in the table click its radio button and click the
(DE)ACTIVATE button.
After adding a virtual server, you can configure it by clicking the radio button to its left
and clicking the EDIT button to display the VIRTUAL SERVER subsection.
1.10.4.1. The VIRTUAL SERVER Subsection
The VIRTUAL SERVER subsection panel shown in Figure 1-32 allows you to configure
an individual virtual server. Links to subsections related specifically to this virtual server
are located along the top of the page. But before configuring any of the subsections related
to this virtual server, complete this page and click on the ACCEPT button.
46
Chapter 1. Red Hat Cluster Suite Overview
Figure 1-32. The VIRTUAL SERVERS Subsection
Name
A descriptive name to identify the virtual server. This name is not the hostname for
the machine, so make it descriptive and easily identifiable. You can even reference the
protocol used by the virtual server, such as HTTP.
Application port
The port number through which the service application will listen.
Protocol
Provides a choice of UDP or TCP, in a drop-down menu.
Virtual IP Address
The virtual server’s floating IP address.
Virtual IP Network Mask
The netmask for this virtual server, in the drop-down menu.
Chapter 1. Red Hat Cluster Suite Overview
47
Firewall Mark
For entering a firewall mark integer value when bundling multi-port protocols or creating a multi-port virtual server for separate, but related protocols.
Device
The name of the network device to which you want the floating IP address defined in
the Virtual IP Address field to bind.
You should alias the public floating IP address to the Ethernet interface connected to
the public network.
Re-entry Time
An integer value that defines the number of seconds before the active LVS router
attempts to use a real server after the real server failed.
Service Timeout
An integer value that defines the number of seconds before a real server is considered
dead and not available.
Quiesce server
When the Quiesce server radio button is selected, anytime a new real server node
comes online, the least-connections table is reset to zero so the active LVS router
routes requests as if all the real servers were freshly added to the cluster. This option prevents the a new server from becoming bogged down with a high number of
connections upon entering the cluster.
Load monitoring tool
The LVS router can monitor the load on the various real servers by using either rup or
ruptime. If you select rup from the drop-down menu, each real server must run the
rstatd service. If you select ruptime, each real server must run the rwhod service.
Scheduling
The preferred scheduling algorithm from the drop-down menu. The default is
Weighted least-connection.
Persistence
Used if you need persistent connections to the virtual server during client transactions.
Specifies the number of seconds of inactivity allowed to lapse before a connection
times out in this text field.
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Chapter 1. Red Hat Cluster Suite Overview
Persistence Network Mask
To limit persistence to particular subnet, select the appropriate network mask from the
drop-down menu.
1.10.4.2. REAL SERVER Subsection
Clicking on the REAL SERVER subsection link at the top of the panel displays the EDIT
REAL SERVER subsection. It displays the status of the physical server hosts for a particular virtual service.
Figure 1-33. The REAL SERVER Subsection
Click the ADD button to add a new server. To delete an existing server, select the radio
button beside it and click the DELETE button. Click the EDIT button to load the EDIT
REAL SERVER panel, as seen in Figure 1-34.
Chapter 1. Red Hat Cluster Suite Overview
49
Figure 1-34. The REAL SERVER Configuration Panel
This panel consists of three entry fields:
Name
A descriptive name for the real server.
Tip
This name is not the hostname for the machine, so make it descriptive and easily
identifiable.
Address
The real server’s IP address. Since the listening port is already specified for the associated virtual server, do not add a port number.
Weight
An integer value indicating this host’s capacity relative to that of other hosts in the
pool. The value can be arbitrary, but treat it as a ratio in relation to other real servers.
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Chapter 1. Red Hat Cluster Suite Overview
1.10.4.3. EDIT MONITORING SCRIPTS Subsection
Click on the MONITORING SCRIPTS link at the top of the page. The EDIT MONITORING SCRIPTS subsection allows the administrator to specify a send/expect string
sequence to verify that the service for the virtual server is functional on each real server. It
is also the place where the administrator can specify customized scripts to check services
requiring dynamically changing data.
Figure 1-35. The EDIT MONITORING SCRIPTS Subsection
Sending Program
For more advanced service verification, you can use this field to specify the path to
a service-checking script. This function is especially helpful for services that require
dynamically changing data, such as HTTPS or SSL.
To use this function, you must write a script that returns a textual response, set it to
be executable, and type the path to it in the Sending Program field.
Note
If an external program is entered in the Sending Program field, then the Send field
is ignored.
Chapter 1. Red Hat Cluster Suite Overview
51
Send
A string for the nanny daemon to send to each real server in this field. By default the
send field is completed for HTTP. You can alter this value depending on your needs.
If you leave this field blank, the nanny daemon attempts to open the port and assume
the service is running if it succeeds.
Only one send sequence is allowed in this field, and it can only contain printable,
ASCII characters as well as the following escape characters:
•
\n for new line.
•
\r for carriage return.
•
\t for tab.
•
\ to escape the next character which follows it.
Expect
The textual response the server should return if it is functioning properly. If you wrote
your own sending program, enter the response you told it to send if it was successful.
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Chapter 1. Red Hat Cluster Suite Overview
Chapter 2.
Red Hat Cluster Suite Component
Summary
This chapter provides a summary of Red Hat Cluster Suite components and consists of the
following sections:
•
Section 2.1 Cluster Components
•
Section 2.2 Man Pages
2.1. Cluster Components
Table 2-1 summarizes cluster components.
Function
Components
Description
Cluster
system-config-cluster Command used to manage cluster
Configuration Tool
configuration in a graphical setting.
Cluster Logical
Volume Manager
(CLVM)
clvmd
The daemon that distributes LVM
metadata updates around a cluster.
It must be running on all nodes in
the cluster and will give an error if
a node in the cluster does not have
this daemon running.
lvm
LVM2 tools. Provides the
command-line tools for LVM2..
system-config-lvm
Provides graphical user interface
for LVM2.
lvm.conf
The LVM configuration file. The
full path is
/etc/lvm/lvm.conf..
54
Chapter 2. Red Hat Cluster Suite Component Summary
Function
Components
Description
Cluster
Configuration
System (CCS)
ccs_tool
ccs_tool is part of the Cluster
ccs_test
Diagnostic and testing command
that is used to retrieve information
from configuration files through
ccsd.
ccsd
CCS daemon that runs on all
cluster nodes and provides
configuration file data to cluster
software.
cluster.conf
This is the cluster configuration
file. The full path is
cman.ko
The kernel module for CMAN.
cman_tool
This is the administrative front end
to CMAN. It starts and stops
CMAN and can change some
internal parameters such as votes.
libcman.so.1.0.0
Library for programs that need to
interact with cman.ko.
clusvcadm
Command used to manually
enable, disable, relocate, and
restart user services in a cluster
clustat
Command used to display the
status of the cluster, including node
membership and services running.
Configuration System (CCS). It is
used to make online updates of
CCS configuration files.
Additionally, it can be used to
upgrade cluster configuration files
from CCS archives created with
GFS 6.0 (and earlier) to the XML
format configuration format used
with this release of Red Hat Cluster
Suite.
/etc/cluster/cluster.conf.
Cluster Manager
(CMAN)
Resource Group
Manager
(rgmanager)
Chapter 2. Red Hat Cluster Suite Component Summary
Function
Fence
55
Components
Description
clurgmgrd
Daemon used to handle user
service requests including service
start, service disable, service
relocate, and service restart
clurmtabd
Daemon used to handle Clustered
NFS mount tables
fence_node
Command used by lock_gulmd
when a fence operation is required.
This command takes the name of a
node and fences it based on the
node’s fencing configuration.
fence_apc
Fence agent for APC power switch.
fence_bladecenter
Fence agent for for IBM
Bladecenters with Telnet interface.
fence_bullpap
Fence agent for Bull Novascale
Platform Administration Processor
(PAP) Interface.
fence_ipmilan
Fence agent for Bull Novascale
Intelligent Platform Management
Interface (IPMI).
fence_wti
Fence agent for WTI power switch.
fence_brocade
Fence agent for Brocade Fibre
Channel switch.
fence_mcdata
Fence agent for McData Fibre
Channel switch.
fence_vixel
Fence agent for Vixel Fibre
Channel switch.
fence_sanbox2
Fence agent for SANBox2 Fibre
Channel switch.
fence_ilo
Fence agent for HP ILO interfaces
(formerly fence_rib).
fence_gnbd
Fence agent used with GNBD
storage.
56
Function
DLM
GFS
Chapter 2. Red Hat Cluster Suite Component Summary
Components
Description
fence_egenera
Fence agent used with Egenera
BladeFrame system.
fence_xcat
Fence agent used with
xCAT-managed cluster.
fence_manual
Fence agent for manual interaction.
NOTE This component is not
supported for production
environments.
fence_ack_manual
User interface for fence_manual
agent.
libdlm.so.1.0.0
Library for Distributed Lock
Manager (DLM) support.
dlm.ko
Kernel module that is installed on
cluster nodes for Distributed Lock
Manager (DLM) support.
lock_gulmd
Server/daemon that runs on each
node and communicates with all
nodes in GFS cluster.
libgulm.so.xxx
Library for GULM lock manager
support
gulm_tool
Command that configures and
debugs the lock_gulmd server.
gfs.ko
Kernel module that implements the
GFS file system and is loaded on
GFS cluster nodes.
gfs_fsck
Command that repairs an
unmounted GFS file system.
gfs_grow
Command that grows a mounted
GFS file system.
gfs_jadd
Command that adds journals to a
mounted GFS file system.
gfs_mkfs
Command that creates a GFS file
system on a storage device.
gfs_quota
Command that manages quotas on
a mounted GFS file system.
Chapter 2. Red Hat Cluster Suite Component Summary
Function
GNBD
57
Components
Description
gfs_tool
Command that configures or tunes
a GFS file system. This command
can also gather a variety of
information about the file system.
lock_harness.ko
Implements a pluggable lock
module interface for GFS that
allows for a variety of locking
mechanisms to be used (for
example, the DLM lock module,
lock_dlm.ko).
lock_dlm.ko
A lock module that implements
DLM locking for GFS. It plugs into
the lock harness,
lock_harness.ko and
communicates with the DLM lock
manager in Red Hat Cluster Suite.
lock_gulm.ko
A lock module that implements
GULM locking for GFS. It plugs
into the lock harness,
lock_harness.ko and
communicates with the GULM
lock manager in Red Hat Cluster
Suite.
lock_nolock.ko
A lock module for use when GFS
is used as a local file system only.
It plugs into the lock harness,
lock_harness.ko and provides
local locking.
gnbd.ko
Kernel module that implements the
GNBD device driver on clients.
gnbd_export
Command to create, export and
manage GNBDs on a GNBD
server.
gnbd_import
Command to import and manage
GNBDs on a GNBD client.
gnbd_serv
A server daemon that allows a node
to export local storage over the
network.
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Chapter 2. Red Hat Cluster Suite Component Summary
Function
Components
Description
LVS
pulse
This is the controlling process
which starts all other daemons
related to LVS routers. At boot
time, the daemon is started by the
/etc/rc.d/init.d/pulse
script. It then reads the
configuration file
/etc/sysconfig/ha/lvs.cf.
On the active LVS router, pulse
starts the LVS daemon. On the
backup router, pulse determines
the health of the active router by
executing a simple heartbeat at a
user-configurable interval. If the
active LVS router fails to respond
after a user-configurable interval, it
initiates failover. During failover,
pulse on the backup LVS router
instructs the pulse daemon on the
active LVS router to shut down all
LVS services, starts the send_arp
program to reassign the floating IP
addresses to the backup LVS
router’s MAC address, and starts
the lvs daemon.
lvsd
The lvs daemon runs on the active
LVS router once called by pulse.
It reads the configuration file
/etc/sysconfig/ha/lvs.cf,
calls the ipvsadm utility to build
and maintain the IPVS routing
table, and assigns a nanny process
for each configured LVS service. If
nanny reports a real server is
down, lvs instructs the ipvsadm
utility to remove the real server
from the IPVS routing table.
ipvsadm
This service updates the IPVS
routing table in the kernel. The lvs
daemon sets up and administers
LVS by calling ipvsadm to add,
change, or delete entries in the
IPVS routing table.
Chapter 2. Red Hat Cluster Suite Component Summary
Function
59
Components
Description
nanny
The nanny monitoring daemon
runs on the active LVS router.
Through this daemon, the active
LVS router determines the health
of each real server and, optionally,
monitors its workload. A separate
process runs for each service
defined on each real server.
lvs.cf
This is the LVS configuration file.
The full path for the file is
/etc/sysconfig/ha/lvs.cf.
Directly or indirectly, all daemons
get their configuration information
from this file.
Piranha Configuration
Tool
This is the Web-based tool for
monitoring, configuring, and
administering LVS. This is the
default tool to maintain the
/etc/sysconfig/ha/lvs.cf
LVS configuration file.
send_arp
This program sends out ARP
broadcasts when the floating IP
address changes from one node to
another during failover.
Table 2-1. Red Hat Cluster Manager Software Subsystem Components
2.2. Man Pages
This section lists man pages that are relevant to Red Hat Cluster Suite, as an additional
resource.
•
Cluster Infrastructure
•
ccs_tool (8) - The tool used to make online updates of CCS config files
•
ccs_test (8) - The diagnostic tool for a running Cluster Configuration System
•
ccsd (8) - The daemon used to access CCS cluster configuration files
•
ccs (7) - Cluster Configuration System
•
cman_tool (8) - Cluster Management Tool
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Chapter 2. Red Hat Cluster Suite Component Summary
•
•
•
cluster.conf [cluster] (5) - The configuration file for cluster products
•
QDisk 1.0 [qdisk] (5) - a disk-based quorum daemon for CMAN / Linux-Cluster
•
fence_node (8) - A program which performs I/O fencing on a single node
•
fence_tool (8) - A program to join and leave the fence domain
•
fence_apc (8) - I/O Fencing agent for APC MasterSwitch
•
fence_bladecenter (8) - I/O Fencing agent for IBM Bladecenter
•
fence_bullpap (8) - I/O Fencing agent for Bull FAME architecture controlled by a
PAP management console
•
fence_ipmilan (8) - I/O Fencing agent for Bull machines controlled by IPMI over
LAN
•
fence_wti (8) - I/O Fencing agent for WTI Network Power Switch
•
fence_brocade (8) - I/O Fencing agent for Brocade FC switches
•
fence_mcdata (8) - I/O Fencing agent for McData FC switches
•
fence_vixel (8) - I/O Fencing agent for Vixel FC switches
•
fence_sanbox2 (8) - I/O Fencing agent for QLogic SANBox2 FC switches
•
fence_ilo (8) - I/O Fencing agent for HP Integrated Lights Out card
•
fence_gnbd (8) - I/O Fencing agent for GNBD-based GFS clusters
•
fence_egenera (8) - I/O Fencing agent for the Egenera BladeFrame
•
fence_manual (8) - program run by fenced as a part of manual I/O Fencing
•
fence_ack_manual (8) - program run by an operator as a part of manual I/O Fencing
High-availability Service Management
•
clusvcadm (8) - Cluster User Service Administration Utility
•
clustat (8) - Cluster Status Utility
•
Clurgmgrd [clurgmgrd] (8) - Resource Group (Cluster Service) Manager Daemon
•
clurmtabd (8) - Cluster NFS Remote Mount Table Daemon
GFS
•
gfs_fsck (8) - Offline GFS file system checker
•
gfs_grow (8) - Expand a GFS filesystem
•
gfs_jadd (8) - Add journals to a GFS filesystem
•
gfs_mount (8) - GFS mount options
Chapter 2. Red Hat Cluster Suite Component Summary
•
•
•
•
gfs_quota (8) - Manipulate GFS disk quotas
•
gfs_tool (8) - interface to gfs ioctl calls
Cluster Logical Volume Manager
•
clvmd (8) - cluster LVM daemon
•
lvm (8) - LVM2 tools
•
lvm.conf [lvm] (5) - Configuration file for LVM2
•
lvmchange (8) - change attributes of the logical volume manager
•
pvcreate (8) - initialize a disk or partition for use by LVM
•
lvs (8) - report information about logical volumes
Global Network Block Device
•
gnbd_export (8) - the interface to export GNBDs
•
gnbd_import (8) - manipulate GNBD block devices on a client
•
gnbd_serv (8) - gnbd server daemon
LVS
•
pulse (8) - heartbeating daemon for monitoring the health of cluster nodes
•
lvs.cf [lvs] (5) - configuration file for lvs
•
lvscan (8) - scan (all disks) for logical volumes
•
lvsd (8) - daemon to control the Red Hat clustering services
•
ipvsadm (8) - Linux Virtual Server administration
•
ipvsadm-restore (8) - restore the IPVS table from stdin
•
ipvsadm-save (8) - save the IPVS table to stdout
•
nanny (8) - tool to monitor status of services in a cluster
•
send_arp (8) - tool to notify network of a new IP address / MAC address mapping
61
62
Chapter 2. Red Hat Cluster Suite Component Summary
Index
M
members status table, 39
A
about this document, i
other Red Hat Enterprise Linux documents, i
C
cluster
displaying status, 39
cluster administration
displaying cluster and service status, 39
cluster components table, 53
Cluster Configuration Tool
accessing, 36
cluster service
displaying status, 39
command line tools table, 33
conventions
document, i
F
feedback, v
L
LVS
direct routing
requirements, hardware, 30
requirements, network, 30
requirements, software, 30
routing methods
NAT, 29
three tiered
high-availability cluster, 27
N
NAT
routing methods, LVS, 29
network address translation
(see NAT)
O
overview
economy, 15
performance, 15
scalability, 15
P
Piranha Configuration Tool
CONTROL/MONITORING, 40
EDIT MONITORING SCRIPTS Subsection,
49
GLOBAL SETTINGS, 41
login panel, 40
necessary software, 40
REAL SERVER subsection, 48
REDUNDANCY, 43
VIRTUAL SERVER subsection
Firewall Mark, 46
Persistence, 47
Scheduling, 47
Virtual IP Address, 46
VIRTUAL SERVER subsection, 45
VIRTUAL SERVERS, 44
R
Red Hat Cluster Manager
components, 53
64
S
services status table, 39
T
table
command line tools, 33
tables
cluster components, 53
members status, 39
services status, 39
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