On Oct 21, 2009, at 11:39 AM, Bela Ban wrote:
This doesn't work currently, as the apache mod-cluster instances
don't exchange information about their states, e.g. which sticky
session is routed to which worker.
No wait, I guess I'm wrong: they don't need to !
Say we have Apaches A1 and A2, and workers W1, W2 and W3.
If a client request hits A2 and A2 creates a new session on W3, then
the session id is going to be SESSION.W3. When the same client now
hits A1, A1 should actually also route the request to W3 ! This of
course assumes that all workers have registered with all Apache
Yes, I'm assuming that.
So IMO we don't even need to exchange routing information between
the Apache daemons... can someone confirm this ?
Good catch, I'll try this today and will let you know!
This is with sticky session. If you turn this off, you can pick any
Apache to route your request, and the route will be different every
time. In this case, you'd have to use synchronous replication to
prevent potentially stale data between 2 requests for the same
session going to different workers.
Yes, we're talking about sticky sessions only, because those who don't
want to have sticky sessions, don't want sessions at all, I think. In
other words if I care about sessions, I want to have sticky sessions
too, otherwise I'm not interested in sticky sessions. Am I wrong?
With Infinispan and DIST, stale data shouldn't be an issue as the
routing is always based on the content (keys to be accesssed) rather
than a client's identity (session-id), and L1 caches should make
things fast, so data doesn't have to be fetched by one worker from
Marek Goldmann wrote:
> Hi all,
> One of JBoss Cloud users asked me about possible clustering of our
> front-end appliances. This in real is the question: can we have
> multiple mod_cluster instances that share state between them?
> If this is possible how I can configure it? If this is not possible
> now, is it maybe in roadmap?
> This could greatly enhance HA of web clusters. How? For example we
> have an Elastic Load Balancer in Amazon. It doesn't support sticky
> sessions and it just forwards requests to selected instances. If we
> could for example forward it to two our clustered front-end
> we could achieve great failover.
Lead JGroups / Clustering Team