Extreme Networks Px Series manual Persistence Modes

Persistence Modes

•Using its configured load balancing policy, the Px series application switch selects one of the web servers. In this example, server 3.

•A three-way TCP handshake is established between the Px series application switch

(C) and server 3 (D).

•The application switch forwards the first data request from the client to server 3 (E).

•The first response from server 3 to the client contains a cookie. (F). The cookie contains the real IP address of the server, 10.1.1.3.

•Each subsequent request sent from the client to the website contains the cookie.

•The application switch examines the cookie and sends each request from this client to server 3. If server 3 fails health checks, the request will be forwarded to another server.

The following Perl example sends a cookie to the user’s browser, and handles the case of server failure. If the chosen server fails, then a request will come to a server that contains the wrong IP address. In this case, the program responds by sending a new cookie that creates persistence to the new server.

#!/usr/bin/perl

#

# Check and set or reset Server Load Balancer host cookie example

#Uses CGI.pm available at CPAN (www.cpan.org)

use CGI qw(:standard);

$SLBCookie = 'sticky_slba'; # Name of cookie SLB switches on

$HostIPAddr = '10.10.10.106'; # This server's private IP Address

$query = new CGI;

$ExistingHostCookie = $query->cookie($SLBCookie); #Retreive the cookie

if ($ExistingHostCookie ne	$HostIPAddr)	{	#If not		set	correctly
$NewHostCookie = $query->cookie(-name=>$SLBCookie,
-value=>$HostIPAddr);			#Build a		new	cookie
print $query->header(-cookie=>$NewHostCookie); #include					in	the	header
}
else {	#	The	cookie	is correct
print $query->header;	#	So	nothing	extra	in	the	header
}

# Example done

Px Series Application Switch Installation and Configuration Guide 6-7