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Local Traffic Policy : Forward Pool and iRule LB::server pool


I'm currently designing a load balanced IIS platform, which will use F5 local traffic policies to send traffic to specific pools based on the http-host of the request*.


I was originally planning on using priority groups and adding a virtual server (with iRules hosting maintenance pages) to each of the pools, but apparently that's not possible SOL10379 (Why!? Makes me want to add a static ARP entry on the Cisco's).


So, my backup solution was to use an iRule which checks [active_members [LB::server pool]] < 1, and then uses the "virtual" keyword to send traffic to my maintenance page virtual server if there aren't any pool members up.


What I'm wanting to know is: How do local traffic policies using forward pool, and iRules checking LB::server pool interact with each other? Will the traffic policy apply first, set the pool, and then the iRule can check if that pool has no active members**, and forward traffic to my maintenance page virtual server?


Notes: A lot of my iRules knowledge of F5s is based on reading these forums for the last couple of weeks, so excuse me if I'm asking something daft.




*So custom health monitors can be defined per website


** I realise the LB::Server pool documentation says if all the pool members are down the default pool will be returned, that's fine because I'll just create a default pool with no active members, and the [active_members [LB::server pool]] check would still be < 1.






For HTTP Request, Request Local traffic policy Event apply first, then the irule HTTP_REQUEST apply.


If you want both interact, you can set a tcl variable in Policy and use it in irule.