findstr

I could never get a 100% solution with only the persist command. Probably my flawed coding, but rather than spin my wheels I switched to the session flavor of persistence so I could store the serverIP. If I get a match, I send the connection directly to the pool member serverIP stored in the session table:

when HTTP_RESPONSE {
  if { [HTTP::cookie exists "JSESSIONID"] } {
    set trimID [lindex [split  [HTTP::cookie "JSESSIONID"] "!" ] 0 ]
    if { [session lookup uie $trimID] equals "" } {
        session add uie $trimID [IP::server_addr] 1800
    }
  }
}
when HTTP_REQUEST {
  if { [findstr [HTTP::uri] "jsessionid" 11 "!"] != ""} {
    pool MyPool member [session lookup uie [findstr [HTTP::uri] "jsessionid" 11 "!"] ]
  } else {
      pool MyPool
  }
}