Controlling session persistence

You may want to tie the requests from one client to the same back-end node using data from the request body. First you need to know what piece of data is always present in every request (ie, a username). You can use the following TrafficScipt rule on a test system to write the data in the request body to the log.

log.info( string.append( " Client", request.getResponseIP(), " -- Body", http.getBody() ) );

For each request that arrives, this rule will log the client IP Address and request body information. You can now examine the logfiles to identify a suitable field to use for session persistence. In this example we are using the username that follows a tag in the request body data. We can now disable the above rule and create a new rule to perform the session persistence based on the username.

$body = http.getBody();

# Extract username.
$match = string.regexmatch( $body, "(.*)", "i" );
if( $match ) {
  $username = $1;
  connection.setPersistenceKey( $username );
  $message = "Username = " . $username;
} else {
  $message = "No username";
}

log.info( $message );

All you need to do now is create a session persistence class called "Universal" and select the persistence type "Universal Session Persistence".

To append to this, on my site i have three webserver pools. However, certain requests must always go to one specific node. TrafficScript easily allows me to perform this:

$path = http.getpath();
$host = http.getHostHeader();

if( string.contains( $path, "ids" ) ) {
        connection.setPersistenceNode ( "web1:80" );
}else if( string.contains( $path, "awstat" ) ) {
        connection.setPersistenceNode ( "web2:80" );
}else if( string.contains( $path, "mailscanner" ) ) {
        connection.setPersistenceNode ( "web2:80" );
}else if( string.contains( $host, "rt" ) ) {
        connection.setPersistenceNode ( "web1:80" );
}else if( string.contains( $host, "webmail" ) ) {
        connection.setPersistenceNode ( "web3:80" );
}

Remember to set your persistence across your pool as 'Named Node'. ZXTM is now free to load balance *all* requests bar the ones i specifically refer to in the above trafficscript. It works a treat!