Support for Cluster Singleton routes
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Key: CAMEL-4454
URL: https://issues.apache.org/jira/browse/CAMEL-4454
Project: Camel
Issue Type: New Feature
Components: camel-core
Affects Versions: 2.8.0
Reporter: Vinicius Carvalho
Priority: Minor
We came up with this problem in our company. I'll try to give a scenario to
show the possible need for this feature:
===================================================================================
The problem
========================================================================================
We have an application bundle in a ear that contains a camel context and some
routes. Due the need of HA of the application, this EAR is replicated over
several nodes. By doing this, our camel context also get replicated. For most
of our usage it's ok to have competing consumers/producers. But we have one
specific case where this is a problem.
In one end is our cluster with several instances, and we rely heavily on JMS.
One specific Queue we use durable subscription to achieve a single consumer on
the cluster, while at the same time, in case of failure another node start
consuming messages.
On the other side, there's an app that uses Hazelcast as a broker for
messaging. We then created a route to consume some messages from the hazelcast
cache to our Queue on the cluster.
Now, if we deploy this route as part of our distribute app, we end with several
instances and messages gets duplicated at the destination on the cluster. We
need only one active route on the cluster.
One could achieve this by deploying the routes to only one app instance, but it
would lead to problems when that instance crashes. So we fixed this by putting
the ear on JBoss deployha-singleton, which offers us the ability to have only
one single active instance at the time. That was ok for us, but we are relying
on specific appserver infrastructure for that.
===================================================================================
Proposal
========================================================================================
If camel somehow used jgroups for instance to comunicate with other instances,
it could use the mechanism that jgroups has to elect a master-view.
Every master-view context would then deploy it's singleton routes. All other
instances would go on passive mode, and have a MessageListener for cluster
messages. In case a view has changed because a node dies, the context would
then check if it is the new master view, and in positive deploy the singleton
routes.
It could be a nice addition to camel on a cluster. Maybe even add the jgroups
support for more features on the core when requesting cluster based
coordination.
I'm currently trying this not at camel level, but we have CDI extension
bootstraping camel (not using camel-pe for some other reasons). And our
extension will then perform this uniqueness in cluster using jgroups to manage
the master node, and invoking context.addRoutes(). We separate the external
routes by using CDI qualifiers on the RoutesBuilder.
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