Cookie Persistence with iRule

Assuming that your unique identifier is really part of the cookie name and not the cookie value, following configuration should work:

class my_nodes {
  "1111 10.1.1.1:80"
  "2222 10.1.1.2:80"
}
pool my_pool {
  select mapclass2node(findstr(http_header("Cookie"), "JServSessionId", 14, 4), my_nodes)
  member 10.1.1.1:80
  member 10.1.1.2:80
}
virtual 1.2.3.4:80 {
  use pool my_pool
}

The basic idea is to use the mapclass2node function to select a node based on unique identifier parsed out of the Cookie header. The call to the findstr function above returns 4 characters at offset 14 after matching string JServSessionId.If the id cannot be parsed out of the cookie or if the cookie header is not present or if the unique id does not match any entry in the class, BIG-IP will loadbalance the request based on loadbalancing method defined for the pool (round-robin in the example above).