jsessionid persistence

JSESSIONID is a cookie... So I'd use hash cookie persistence on the cookie JSESSIONID myself rather than a custom iRule... It's quicker and less prone to issues unless you have something specific required that means you need more control (but as you're essentially doing what the hash does anyway, I can't see the irule would be better in this unstance)

Also make sure your action on service down is set appropriately for when ghe node fails...

H