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<title>ActiveMQ Artemis JMS Symmetric Cluster Example</title>
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<h1>JMS Symmetric Cluster Example</h1>
<pre>To run the example, simply type <b>mvn verify</b> from this directory, <br>or <b>mvn -PnoServer verify</b> if you want to start and create the server manually.</pre>
<p>This examples demonstrates a <b>symmetric cluster</b> set-up with ActiveMQ Artemis.</p>
<p>ActiveMQ Artemis has extremely flexible clustering which allows you to set-up servers in
many different topologies.</p>
<p>The most common topology that you'll perhaps be familiar with if you are used to application
server clustering is a <b>symmetric cluster</b>.</p>
<p>With a symmetric cluster, the cluster is homogeneous, i.e. each node is configured the same
as every other node, and every node is connected to every other node in the cluster.</p>
<p>By connecting node in such a way, we can, from a JMS point of view, give the impression of distributed
JMS queues and topics.</p>
<p>The configuration used in this example is very similar to the configuration used by ActiveMQ
when installed as a clustered profile in JBoss Application Server.</p>
<p>To set up ActiveMQ Artemis to form a symmetric cluster we simply need to mark each server as <code>clustered</code>
and we need to define a <code>cluster-connection</code> in <code>broker.xml</code>.</p>
<p>The <code>cluster-connection</code> tells the nodes what other nodes to make connections to.
With a <code>cluster-connection</code> each node that we connect to can either be specified
indivually, or we can use UDP discovery to find out what other nodes are in the cluster.</p>
<p>Using UDP discovery makes configuration simpler since we don't have to know what nodes are
available at any one time.</p>
<p>Here's the relevant snippet from the server configuration, which tells the server to form a cluster
with the other nodes:</p>
<pre class="prettyprint">
<code>
<cluster-connection name="my-cluster">
<address>jms</address>
<connector-ref>netty-connector</connector-ref>
<retry-interval>500</retry-interval>
<use-duplicate-detection>true</use-duplicate-detection>
<message-load-balancing>STRICT</message-load-balancing>
<max-hops>1</max-hops>
<discovery-group-ref discovery-group-name="my-discovery-group"/>
</cluster-connection>
</code>
</pre>
<p>In this example we create a symmetric cluster of six live nodes, and we also pair each live node
with it's own backup node. (A backup node is not strictly necessary for a symmetric cluster).</p>
<p>In this example will we will demonstrate this by deploying a JMS topic and Queue on all nodes of the cluster
, sending messages to the queue and topic from different nodes, and verifying messages are received correctly
by consumers on different nodes.</p>
<p>For more information on configuring ActiveMQ Artemis clustering in general, please see the clustering
section of the user manual.</p>
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