This article describes how to configure rule-based persistency on a NetScaler appliance.

Background

When rule-based persistence is configured, the appliance creates a persistent session based on the contents of the matched rule before directing the request to the service selected by the configured load balancing method. Subsequently, it directs all requests that match the rule to the same service.

Using rule-based persistency on a load balancing virtual server, along with two advanced expressions, allows the appliance to persist network traffic to a specific service, based for example on a session cookie. One of the expressions is used to capture the cookie value from the HTTP response and the other expression to make a persistence decision on the next HTTP request with the session cookie.

Instructions

To configure the rule-based persistency on a NetScaler appliance, run the following commands:
add policy expression rule_based_persistence_request "HTTP.REQ.HEADER(\"cookie\").VALUE(0).TYPECAST_NVLIST_T(\'=\',\';\').VALUE(\"TestCookie\")"
add policy expression rule_based_persistence_response "HTTP.RES.HEADER(\"set-cookie\").VALUE(0).TYPECAST_NVLIST_T(\'=\',\';\').VALUE(\"TestCookie\")"
add lb vserver lb-vserver-http HTTP 10.12.42.170 80 -persistenceType RULE -lbMethod ROUNDROBIN -rule rule_based_persistence_request -resRule rule_based_persistence_response
add service red-service red-server HTTP 80
add service blue-service blue-server HTTP 80
bind lb vserver lb-vserver-http red-service
bind lb vserver lb-vserver-http blue-service

Rum the following command to verify if the persistency is configured accurately:
> show lb vserver <name>

lb-vserver-170-http (10.12.42.170:80) - HTTP Type: ADDRESS
State: UP
Last state change was at Sat Aug 25 05:49:45 2012
Time since last state change: 33 days, 05:43:07.840
Effective State: UP
Client Idle Timeout: 180 sec
Down state flush: ENABLED
Disable Primary Vserver On Down : DISABLED
Appflow logging: DISABLED
Port Rewrite : DISABLED
No. of Bound Services : 2 (Total) 2 (Active)
Configured Method: ROUNDROBIN
Rule: rule_based_persistence_request
RespRule: rule_based_persistence_response
Mode: IP
Persistence: RULE Persistence Timeout: 2 min
Vserver IP and Port insertion: OFF
Push: DISABLED Push VServer:
Push Multi Clients: NO
Push Label Rule: none
L2Conn: OFF
IcmpResponse: PASSIVE
1) red-svc (10.12.59.213: 80) - HTTP State: UP Weight: 1
2) blue-svc (10.12.59.212: 80) - HTTP State: UP Weight: 1

To test this configuration, you can create a PHP file setcookie.php within the Web site root folder and then use the PHP function setcookie to set a test cookie on the HTTP response.The setcookie.php file contains the following content:

<?php
$value = 'red-server';
setcookie("TestCookie", $value);
?>

The first HTTP request does not contain the session cookie. At this point the appliance makes a load balance decision.
http://lbvserver.hv.lab/setcookie.php

GET /setcookie.php HTTP/1.1
Host: lbvserver.hv.lab
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:8.0.1) Gecko/20100101 Firefox/8.0.1
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip, deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Connection: keep-alive
Range: 5
test-header: testing

The script has set the cookie on the response. At this moment, the NetScaler appliance uses the red-server as the persistence parameter.

HTTP/1.1 200 OK
Date: Thu, 27 Sep 2012 15:56:06 GMT
Server: Apache/2.2.3 (CentOS)
X-Powered-By: PHP/5.1.6
Set-Cookie: TestCookie=red-server
Content-Length: 110
Connection: close
Content-Type: text/html; charset=UTF-8

Second HTTP request contains the session cookie. At this point, the NetScaler appliance makes persistence decision.

GET /setcookie.php HTTP/1.1
Host: lbvserver.hv.lab
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:8.0.1) Gecko/20100101 Firefox/8.0.1
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip, deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Connection: keep-alive
Cookie: TestCookie=red-server
Range: 5
test-header: testing

The following command shows an entry on the persistence table and the persistence parameter being used:
> show persistentSessions

Type SRC-IP DST-IP PORT VSNAME TIMEOUT PERSISTENCE-PARAMETER
RULE 0.0.0.0 10.12.59.213 80 lb-vserver-http 0 red-server
Done