[SOLVED] f5 LTM irule - can a pool name be generated in an irule

f5 LTM irule - can a pool name be generated in an irule

I need to setup a configuration for many similar environments. Each will have a different hostname that follows a pattern, e.g. env1, env2, etc.

I can use a pool per environment and a single virtual server with an irule that selects a pool based on hostname.

What I'd prefer to do is dynamically generate and select the pool name based on the requested hostname rather than listing out every pool in the switch statement. It's easier to maintain and automatically handles new environments.

The code might look like:

when HTTP_REQUEST {
  pool [string tolower [HTTP:host]]
}

and each pool name matches the hostname.

Is this possible? Or is there a better method?

EDIT

I've expanded my hostname pool selection. I'm now trying to include the port number. The new rule looks like:

when HTTP_REQUEST {
  set lb_port "[LB::server port]"
  set hostname "[string tolower [getfield [HTTP::host] : 1]]"
  log local0.info "Pool name $hostname-$lb_port-pool"
  pool "$hostname-$lb_port-pool"

}

This is working, but I'm seeing no-such-pool errors in the logs because somehow a port 0 request is coming into the pool. It seems to be the first request and the followed by the request with the legitimate port.

Wed Feb 17 20:39:14 EST 2016    info    tmm tmm[6519]       Rule /Common/one-auto-pool-select-by-hostname-port <HTTP_REQUEST>: Pool name my.example.com-80-pool
Wed Feb 17 20:39:14 EST 2016    err tmm1    tmm[6519]   01220001    TCL error: /Common/one-auto-pool-select-by-hostname-port <HTTP_REQUEST> - no such pool: my.example.com-0-pool (line 1) invoked from within "pool "$hostname-$lb_port-pool""
Wed Feb 17 20:39:14 EST 2016    info    tmm1    tmm[6519]       Rule /Common/one-auto-pool-select-by-hostname-port <HTTP_REQUEST>: Pool name my.example.com-0-pool

What is causing the port 0 request? And is there any workaround? e.g. could I test for port 0 and select a default port or ignore it?

ONE MORE EDIT

Rebuilt the virtual server, and now the error has gone. The rebuild of the VS was just to rename it though. I'm fairly sure I recreated the settings exactly the same.

Solution

Yes, you can specify the pool name in a string. What you have there would work as long as you have a pool with that same name. Though it doesn't show an example of doing it this way, you can also check out the pool wiki page on DevCentral for more information.

As an aside, in my environment I generally create pools with the suffix _pool to distinguish them from other objects when looking at config files. So in my iRules, I would do something like this (essentially the same thing):

when HTTP_REQUEST {
    pool "[string tolower [HTTP::host]]_pool"
}