[mod_cluster-dev] Failover failed

Bela Ban bela at jboss.com
Fri Dec 19 10:10:39 EST 2008

Paul Ferraro wrote:
>> CTRL-C.
> That will shutdown gracefully, triggering all of the appropriate 
> shutdown events.

Good to know

>>>> * Now I have 80 failed clients and 0 active clients !
>>> OK - that's weird. Let me try to reproduce this on my end.
>> OK
> I could not reproduce this. The only threads that should report errors
> are the ones that were currently being processed by that server - these
> will not failover to the other server. Though it is unlikely that all
> 80 threads were all being processed (i.e. not queued) by the server that
> you stopped, I'm not sure what else could cause all 80 clients to fail.
> Please regurgitate all of the input values you used in the demo app.

OK. I'll try to reproduce this problem and make sure to write down the 
exact steps if I can reproduce it.

>>>> * If I call Server.shutdown() on node2 (via JMX), then node1 serves
>>>> 40 sessions. But why does node1 not pick up the other 40 sessions
>>>> from left node2 ? Is this the client, which simply terminates
>>>> threads which got a 500 ?
>>> Yes
>> Why don't we change that, and ignore HTTP error responses ? This way,
>> eventually, all clients would fail over to the running node.
> I should clarify - not all requests failover - only those requests not
> yet accepted by target server's connector. It would be dangerous to
> failover requests already accepted by the target connector.

Can this be configured ? In mod-jk, there were IIRC 4 configuration 
possibilities for retrying

>> Agreed. But the graceful shutdown case (maybe complemented with a
>> shutdown hook) should allow us to tell httpd to redirect requests for
>> all apps of a given node before the node shuts down.
> We are doing that. Currently, mod_cluster responds to context and
> server STOP_EVENTs. Really, we should be using BEFORE_STOP_EVENT to
> notify mod_cluster before any threads are interrupted. I've made this
> change in trunk.


Bela Ban
Lead JGroups / Clustering Team
JBoss - a division of Red Hat

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