Hi,
We have a Tomcat Cluster consisting of 2 servers that replicate their sessions
with the following
configuration in server.xml (directly under <Engine..>):
...
<Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster">
<Channel className="org.apache.catalina.tribes.group.GroupChannel">
<Membership
className="org.apache.catalina.tribes.membership.McastService"
address="228.0.0.7" port="42223" />
</Channel>
</Cluster>
...
When I do a 'tcpdump host 228.0.0.7' on both servers, I see the following:
on server1:
...
<timestamp> IP server1.42223 > 228.0.0.7.42223: UDP, length 69
<timestamp> IP server1.42223 > 228.0.0.7.42223: UDP, length 69
<timestamp> IP server1.42223 > 228.0.0.7.42223: UDP, length 69
...
on server2:
...
<timestamp> IP server2.42223 > 228.0.0.7.42223: UDP, length 69
<timestamp> IP server2.42223 > 228.0.0.7.42223: UDP, length 69
<timestamp> IP server2.42223 > 228.0.0.7.42223: UDP, length 69
...
The strange thing is that when I restart one server, the other server keeps
showing the same tcpdump-output,
but the restarting server sees both servers for a few minutes and after a while
only itself again.
Thankfully this means the membership is established and sessions are correctly
replicated between the 2 nodes,
but still, this situation signals a problem.
It should be noted that both servers are virtual machines on different
(Proxmox) hosts.
We have several Tomcat Clusters in our network of which some show similar
problems.
However, some time ago one cluster consisting of 2 dedicated servers (i.e. no
virtual machines) showed a similar problem.
After we modified the multicast-address to a unique one (228.0.0.X), it seemed
to have been fixed.
The fix didn't work in this case though.
I was thinking the problem might be found towards our switches that don't
handle multicast well, but then
again, why was the fix on another Tomcat Cluster to adjust the
multicast-address? Maybe the problem lies more
towards the fact that these servers are virtual machines.
I'm hoping someone can provide some suggestions to identify the exact problem
(and the solution:)).
Regards,
Willem
--
Willem Fibbe
Teamleider Systeembeheer
Realworks BV
A: W.G. Plein 516, 1054 SJ Amsterdam
T: +31 20 4 120 120
F: +31 20 4 120 127
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