[jboss-dev-forums] [Design of Messaging on JBoss (Messaging/JBoss)] - Re: Server side HA and failover

[timfox]

"bstansberry at jboss.com" wrote : 
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  | The stuff that should be reused is the interceptor model.  
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This is the client side interceptor model?

anonymous wrote : 
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  | 2) The JGroups view can't be used directly, as a JGroups Address is not suitable for use as a Remoting InvokerLocator. At minimum a different port.  Quite possibly a different IP address (e.g. client connections use a different NIC than clustering traffic.)  I think the thing to do is something like adding another Request type where a server publishes its InvokerLocator(s); the rest of the cluster maintains a map of that data.  That's basically the DistributedReplicantManager concept.
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I think we would need to replicate both the remoting invoker locator and the JGroups address.
The client needs to know the locator list but a particular server also needs to know who it's failover server(s) are, this is so it can do stuff like cast messages to it's failover servers when we do in memory message replication. A JGroups address would be ideal for this.
We should be able to support multiple failover servers for a particular server.

anonymous wrote : 
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  | Perhaps an approach where the client fails over to anyone, but if the server isn't the appropriate one it communicates that back to the client, along with the updated topology and info as to who the failover server should be.
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I like this idea.


anonymous wrote : 
  | Stupid question: why does the client need to fail over to a particular server?  The failover server needs to do work to recover persistent messages from the store, but once it's done that, aren't they available to a client connecting to any server?

Each server maintains it's own set of queues each containing different sets of messages.
So when a node fails the failover node needs to take over responsibility for the queues on the node that failed.
This means creating those queues in memory and loading any persistent messages from storage into those queues (if in memory replication is being used the messages will already be there so no need to load from storage).
This means clients need to reconnect the node which now hosts those queues so they can continue as if nothing happened.

As an added complication we also need to decide what happens when the failed node comes back to life.

Does it take over responsbility for the original queues it has?

Actually I don't think this is possible unless there are no clients using those queues on the failover node, since we would have to disconnect and reconnect the connections on the resurrected node which would mean losing any persistent messages delivered in those sessions which would be unacceptable.


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