Sticky Sessions which aren’t

Exhibt A (the Apache 2.2 mod_proxy documentation): 

stickysession Balancer sticky session name. The value is usually set to something like JSESSIONID or PHPSESSIONID, and it depends on the backend application server that support sessions. If the backend application server uses different name for cookies and url encoded id (like servlet containers) use | to to separate them. The first part is for the cookie the second for the path.


Exhibit B (the Apache 2.2 mod_proxy code):

     * If we found a value for sticksession, find the first '.' within.
     * Everything after '.' (if present) is our route.
    if ((*route) && ((*route = strchr(*route, '.')) != NULL ))
    if ((*route) && (**route)) {
        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                                  "proxy: BALANCER: Found route %s", *route);
        /* We have a route in path or in cookie
         * Find the worker that has this route defined.
        worker = find_route_worker(balancer, *route, r);
        if (worker && strcmp(*route, worker->s->route)) {
             * Notice that the route of the worker chosen is different from
             * the route supplied by the client.
            apr_table_setn(r->subprocess_env, "BALANCER_ROUTE_CHANGED", "1");
            ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                         "proxy: BALANCER: Route changed from %s to %s",
                         *route, worker->s->route);
        return worker;

Translation: In Apache mod_proxy_balancer, sitcky sessions need to be in the format <cookie value>.<route> where route refers to the backend server. 


There are a couple of useful docs about this: Mark Round and the Jetty Docs. Normally I’d submit a patch to the Apache docs to clear this up, but unfortunately I haven’t been able to get failover between servers working correctly, so I’m not convinved I completely understand all the issues yet.

However, once you have got this working it turns out to be a case of RTFM.

Exhibit C:

route Route of the worker when used inside load balancer. The route is a value appended to session id.

I’d argue that only makes any sense after you’ve got it working…

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