Priority Group Activation Failback with HTTP Cookie Insert

The overriding principle of persistence is that once a client has established a session to a pool member, it should stay there until the session expires. This is to prevent unexpected session failure due to changing pool member servers.

If a client has a session to the low priority server when the high priority servers are back up, the cookie persistence will keep returning the client to the low priority server until the cookie expires, so that the user sessions do not break.

If this behaviour is not desired, you will need to write an irule that looks at the load-balancing decision and the available members in the pool to determine whether the low priority pool member has been selected, whether any high priority pool members are available, and make a new load-balancing decision based on that information.