LTM - Load Balancing iRule

Hi Dave,

Okay, I am surprised there are two tcp connections. That would seem like round robin algorithim is not working. Could it be that there is other traffic hitting this vip? Perhaps nagios/sitescope/opennms/etc monitor traffic making requests to verify it is up? That would of course skew the alternation

Here is an irule that uses a global variable (to retain across tcp sessions). One draw back to this irule is that it will use only one core/tmm of your LTM, but that might be okay if you aren't pushing the LTM to its max limits. If someone knows a way to do this without using a writable global var, I would be keen to know.

You will need to add in the internal IP's of your member servers in the variables where 1.1.1.1 and 1.1.1.2 are prefilled

when RULE_INIT {
   set ::global_myvsconncnt 0
}

when CLIENT_ACCEPTED {
   set member1 "1.1.1.1 80"
   set member2 "1.1.1.2 80"
   set pool [LB::server pool]

   incr ::global_myvsconncnt
   if { $::global_myvsconncnt > 1 } {
      set ::global_myvsconncnt 0
      pool $pool member $member1
   } else {
      pool $pool member $member2
   }
}

Come to think of it, if you do/may have the odd user hitting this vip in addition to the client or perhaps you have a monitoring system hitting it, we could easily add a source IP check in this irule to only apply the alternating logic to the requests coming from your client source IP. Then you could guarantee that of their two connections, one will always be on one member server and the other on the other. Additionally, logic could be added to check if the target member server is actually down in the pool and send to the other one until it is back up. Perhaps the pool member command will do this automatically if attempting to pool member a connection to a down member

Hope this helps. If it does please mark the answer as correct