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Re: [xmlblaster] Cluster peers

Michael Lum wrote:
Hi Marcel!
Thanks for getting back to me so quickly. I've attached a diagram of what I have in mind. It's basically akin to setting up 'multicast domains' where the routing logic doesn't only check to see if it is the master, it also checks to see if it should both handle locally as well as forward to another master or lower stratum.

Is there anything I can provide to help? Is this something I could achieve by writing a custom clustering plugin? 

Principally your configuration should be possible.
Why do you need the mirrored master? For fail over (HA)?

Unfortenately, for master mirroring a plugin is not enough:

xmlBlaster/src/java/org/xmlBlaster/engine/cluster/ClusterManager.java:369
does for example forwardPublish().

This calls getConnection() which is implemented on line 627.
If you change the return type to return an array (or a Set)
of "NodeDomainInfo" (which is the found master or the stratum nearer to the master)
instances instead of only one
you could address two or more masters.

You would need to remove the "break;" on line 698 and
than handle multiple higher priority masters in all follow up code.

OR probably a better approach is that the message is only routed
to its single master and when the master is reached this one mirrors it
to neighbour masters (what about fail over in this case?).

Just play a bit in those code sections and report your
success.
Please use the current code from svn for this so we can
easily add your patch.

best regards
Marcel





Thanks
Mike

On 03/01/05 12:48, Marcel Ruff wrote:

Michael Lum wrote:

Hello,

I couldn't figure this out from the reference book and didn't find anything on the mailing list --

How can I setup two nodes in a cluster to be peers? I'd like to put two machines behind a load balancer, so that any client could publish a message, but it might end up on one of the two machines depending on where the load balancer sends it. Also, subscribers would connect via the load balancer, so any subscriber might end up on one of the two machines. But, I need any message published to any of the two machines to be receieved by all subscribers, so if a client connects publishes to server 'A', subscribers on server 'A' AND on server 'B' get copies of the message.

Finally, if possible, I'd like these two nodes to be slaves to a pair of masters, so that both the two slaves that are peered AND the two masters (also peered) are getting copies of messages.

Thanks...

Mike 



Mike,

these are nice features which are not available yet,
but xmlBlaster should definitely support such scenarios
in the near future.

1. load balancer
  I could imagine that the load balancer initially chooses
  an IP of one of the xmlBlaster slaves and the client sticks
  to it until it is finished or until the connected xmlBlaster
  server stops.
  If the load balancer shall intercept each publish call
  you need to have sort of a proxy running on the load balancer.
  In the simplest case this is a xmlBlaster slave itself
  or a sligthly extended SOCKET protocol plugin ...

2. master slave operation
  This is available already.

3. master mirroring
  I believe you need this feature of having two masters
  to have high availability (HA) support.
  This is currently not supported directly by xmlBlaster
  but we are not far away of it.
  Probably it can be handled by a master/slave operation
  of the two backends and by a dynamic reconfiguration
  from slave to master when the original master breaks away.
  Here the typical cluster reconfiguration logic applies,
  they need a heart beat and a solid decision which of the
  remaining sub clusters takes over control in case of problems.
  -> Depending on your exact use case the existing
     master / slave could be sufficient

Sorry, no out-of-the-box solution yet,

regards,
Marcel



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