This article describes how to configure the Responder feature to display user specific message when the rate limit for active connections exceeds on a NetScaler appliance.

Background

When the backend servers are unable to process the client connections periodically because of the maxconn setting or resource constraints on the servers, these connections are placed in the Surge Queue. To store the client connections, the Surge Queue utilizes the memory space. If the appliance runs out of memory because of a high volume Surge Queue, the appliance cannot allocate enough memory to the NetScaler Buffer (NSB). This can impact the performance of the services and virtual servers on the appliance.

You can configure the Spillover feature to resolve such an issue. Refer to CTX127915 – How to Configure the Static Spillover Feature of a NetScaler Appliance to Control the High Volume Surge Queue to configure the Spillover feature on a NetScaler appliance.

Note: If you do not want to configure the Spillover feature, you can configure the Responder feature to avoid this scenario.

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Instructions

To configure the Responder feature to display user specific messages when the rate limit for active connections exceeds on an appliance, complete the following procedure:

1. Run the following command from the command line interface of the appliance, to create a content switching virtual server:
   add cs vserver cs-citrix-80 HTTP 10.102.70.81 80 -cltTimeout 180

2. Run the following command to create a service:
   add service s[1-5] 10.201.213.[1-5] HTTP 80  -maxClient 200

3. Run the following command to create a Load Balancing virtual server:
   add lb vserver lb-cs-citrix-80 HTTP 0.0.0.0 0 -persistenceType NONE -cltTimeout 180

4. Run the following command to bind the Load Balancing virtual server to the Content Switching virtual server:bind cs vserver cs-citrix-80 -lbvserver lb-cs-citrix-80

5. Run the following command to bind the service to the Load Balancing virtual server:
   bind lb vserver lb-cs-citrix-80 s[1-5]

6. Run the following command to create a Responder action:
   add responder action rsact1 respondwith "\"HTTP/1.1 503 Server Busy\r\n\r\n\""

7. Run the following command to create a limit selector to provide a PIXL expression to be used by the limitIdentifier:
   add stream selector rsel1  CLIENT.IP.SRC

8. Run the following command to create a limit identifier to provide a threshold value for the active connections:add ns limitIdentifier rslm1 -threshold 1000 -mode CONNECTION -selectorName rsel1

9. Run the following command to create a Responder policy:
   add responder policy rspol1 "SYS.CHECK_LIMIT(\"rslm1\")" rsact1

10. Run the following command to bind the responder policy to the Load Balancing virtual server:
    bind lb vserver lb-cs-citrix-80 -policyName rspol1 -priority 1 -gotoPriorityExpression END

Note: When you configure the responder policy with Rate Limiting, you cannot use the Dynamic Spillover feature. Because, you must specify a threshold that cannot be changed. You can use a Responder policy without configuring the Spillover feature on the virtual servers.

This article describes how to configure the Responder feature to display user specific message when the rate limit for active connections exceeds on a NetScaler appliance.