Issue with multiple pool on LTM

The simple answer is the F5 LTM is clever and reads the iRules for commands like pool, node and virtual and can if used can identify if a Virtual Server has an possible backend destination that is up or not. If all possible destinations are down the VS will be down however if one is up the F5 LTM will leave the VS as up.

The fix is a little odd but simple, do not use explicit destination in your iRules. What this means is set your destination to a variable first then when the LTM reads the iRule it will not be able to lookup the pool/node/virtual server.

I have taken a sample of your iRule to show as an example:

when HTTP_REQUEST {
    if { ([HTTP::path] starts_with "/CPCi/") } { pool cpc-443 }
    elseif { ([HTTP::query] contains "target=hvnplwspwa41") } {
        set destNode "10.18.139.71"
        node $destNode 443
...
    
...
    } elseif {([HTTP::path] starts_with "/prwebGCS/IAC")} {
        set destPool gcsp-443
        pool $destPool
...
    

There maybe another way to do this I don't know about but I have found this works and most of the time try to avoid being explicit with any forwarding command in iRules (keeps my code more generic)