Is there any way in an iRule to tell if APM is enabled or disabled on a connection?

Do you want the connection to be logged, that gives you the output of Enabled or Disabled for troubleshooting purposes?

If you are using ACCESS::disable then the easiest way would be to set a user defined tcl variable to indicate the state. I have found no combination of built-in commands that is completely error proof or that require complicated parameter passing.

ACCESS::disable
set access_disabled 1

if {$access_disabled} {
     Do Stuff outside of APM
}

You might be able to get ACCESS::session sid working but this also requires that you code an if check to do a sting comparison which I guess would be more CPU expensive than doing an integer check with your own variable.

Hi,

if you want to do some stuff when APM is enabled, you can do it on ACCESS_ACL_ALLOWED event.

this event raise every time the request is associated with APM session and not dropped by ACL (if no ACL is defined or explicit ACL allow the request)

you can also use this irule :

when HTTP_REQUEST {
    set apm_enabled 0
}

when ACCESS_ACL_ALLOWED {
    set apm_enabled 1
}

when HTTP_REQUEST_SEND {
    log "APM Status is $apm_enabled"
}