Citrix health check monitor User manual

How Do I configure health check monitors on NetScaler?

Use Case

George wishes that his Application Delivery Controller (ADC) must take real time decisions related to the traffic flowing through it. He wants his load balancing set up to work efficiently all the time and requires that the ADC must take smart routing decisions based on any change in the availability of the backend servers.

Introduction to health check monitors

An Application Delivery Controller must be able to take smart real time decisions based on the status/availability of the backend servers. It must effectively divert traffic from any non-responsive backend server and continue to send that traffic to an alternate load balanced server that is available.

For this purpose, a user can set up health checks or monitors on the ADC. The job of these monitors is to test the availability of the backend servers by probing these servers at regular intervals.

Health check monitor support on NetScaler

As we know, backend servers are represented as services on the NetScaler ADC.

To test the availability of any backend server we can set up monitors and bind these monitors to the services configured on NetScaler. These monitors then probe the backend server at regular intervals

(defined during monitor configuration) and accordingly update the status of the service as

UP/DOWN. If the backend server responds to the probes as per the configured settings (number of probes, response time, etc) then the service will be marked as UP else it will be marked as DOWN.

Once a service is marked as DOWN, those services are no longer considered as valid traffic destination by the virtual server to which they are bound. The LB virtual sever will not send any requests to this service until the service is again marked as UP.

Each monitor maps to one type of traffic. Hence it is also possible to bind multiple monitors to one service where in different monitors would be monitoring different part of traffic with respect to the backend server.

The NetScaler has many built-in monitors for common types of services. Apart from these, you can also create a custom monitor if no pre-configured monitor exists for the type of monitor you need.

The configuration for these will be explained in the next section.

Note: You cannot delete built-in monitors

Configuration Steps

In NetScaler, whenever a service is created, a monitor is by default attached to this service.

If you need to bind another built-in monitor to the service (for monitoring different type of traffic), you must follow the below mentioned steps.

Example: User wants to bind PING monitor to a service.

Step 1: View the built-in monitor and ensure that the set values are as per your requirements

On CLI: show monitor ping

To change any settings we can use the set lb monitor command

Example: set lb monitor <monitorName> <type> [-interval <integer> [<units>]

Set lb monitor ping PING interval 4

On GUI: Go to Traffic Management >> Load Balancing >> Monitors. Select the built-in monitor that is of your interest and click on Edit.

Ensure that the values are as per your requirements

Step 2: Bind this monitor to the service

On CLI: To bind a monitor to a service use the following command bind service <servicename> -monitorName <string>

Example: bind service service1 –monitorName PING

On GUI: Go to Configuration >> Traffic Management >> Load Balancing >> Service and select the service that you need to bind the monitor to.

Go to section ‘Monitors’, select the built-in monitor you wish to bind to this service and Click on

Bind.