Best Way to do Cookie Persistence here?

I believe that you are trying to replace the default behavior of the F5 Persistence Cookie and compensate for Pool Member failures with an iRule. You shouldn't have to do either since those features are available through Virtual Server and Pool setup options.

 

 

Use Default Cookie Behavior (Tracks the Pool and Pool Member selected by whatever Load Balancing Method is configured - Round Robin, Least Connections (Node), Least Connections (Member), etc):

 

HTTP Cookie Insert: Specifies that the system inserts server information, in the form of a cookie, into the header of the server response. This is the default setting.

 

 

If Pool Member Fails:

 

Set Pool setting "Action On Service Down" to "Reselect".

 

 

This should give you the behavior that you are looking for and decrease the setup complexity.