multi pool irule

You could also add some logging to see if you can verify things are going where they are supposed to... Also, if you're getting a 404 and the logs (in /var/log/ltm) say it's changing to the admin pool, then it would seem like your URI is bad.

when HTTP_REQUEST { 
    if {[HTTP::uri] contains "/admin"} { 
        log local0. "Changing to ADMIN pool: [HTTP::uri]"
        pool ADMIN-http-farm 
    } else { 
        log local0. "Default pool: [HTTP::uri]"
        pool CXF-http-farm 
    } 
}