apm irule, unexpected result - variable scope not standard?

Firstly, to get an understanding of the flow, you can check out this article describing the APM event flow. Because you won't have a single request that ends up hitting both

ACCESS_POLICY_COMPLETED

and

ACCESS_ACL_ALLOWED

, you can't share variables between them (since variables live and die with the request). Session variables are more persistent and can be accessed as throughout the session. I think that should help answer your first question.

For your second question, RULE_INIT sets a variable when you save the iRule, so it's a global variable. Try changing your irule to use

set ::entrypoint

and

set ::backend_host

instead and then reference them the same way (e.g.

HTTP::uri $::entrypoint

). See if that helps.