clearing cookie on persisted sessions when pool member is down

Hi-

 

 

I am writing an iRule to detect a server crash - which I am defining as anytime a request gets a 500+ error code. On this event, I'd like to try other pool members before allowing the error to return the user's browser. I found this post which is basically what I would like to do - but that post is several years old. One thing I have going for me that should make all this easier is that we are actually a software vendor and I am trying to demonstrate roughly how a customer could use our product in a highly available environment. My script will never be used in production, just a simple demo where I can control things easily. So this thing doesn't need to be bullet proof.

 

 

What I am seeing from BIG IP is that if I kill a server, the health monitor picks that fact up and marks the pool member down. This is what I expect. On the next request from a session that was persisted to the failed node, BIG IP selects the other node automatically (again this makes sense). However, my application is stateful and recovering that state requires that I clear a cookie. It is possible that I can handle the situation more gracefully in my application, but I am curious if there is a way in the LB_SELECTED event to tell that a different node has been selected than what was used on previous requests. If I can detect this situation, I could clear the cookie and my app would probably be pretty happy then.

 

 

It seems one possibility is to capture any existing persistence in HTTP_REQUEST and then in LB_SELECTED I could check if some other node is selected.

 

Or maybe in HTTP_REQUEST I could just check the status of the pool member for any existing persistence and remove the persistence if the member is down?