<div class="wiki-content maincontent"><p>Durable subscribers behave a little differently across a cluster of ActiveMQ brokers. The two main issues surround messages getting stuck on other brokers in the network after a durable subscriber has disconnected and reconnected to a different broker in the network without fully unsubscribing. The reasons for disconnecting/reconnecting can be voluntary (where the subscriber is using the failover transport), or involuntary (one of the brokers in the cluster fails).</p>

<p>For example, if you have two brokers A and B networked together in both directions to form a cluster, and a durable subscriber connects to broker B, a producer P on broker A will have its messages properly forwarded to broker B and the durable subscriber. However, if the subscriber disconnects and reconnects to broker A, any messages sent by P while the subscriber was away will be stuck on B until the subscriber reconnects to B. </p>

<p>The solution is to use <a shape="rect" href="virtual-destinations.html">Virtual Destinations</a></p>

<p>Virtual topics use queues under the covers and this allows ActiveMQ to treat each subscriber as a plain old Queue subscriber. This allows ActiveMQ to replay messages that have been orphaned on another broker in the cluster using this configuration as explained in the <a shape="rect" href="networks-of-brokers.html">Networks of Brokers</a> documentation:</p>

<div class="code panel pdl" style="border-width: 1px;"><div class="codeContent panelContent pdl">
<pre class="brush: java; gutter: false; theme: Default" style="font-size:12px;">    &lt;destinationPolicy&gt;
      &lt;policyMap&gt;
        &lt;policyEntries&gt;
          &lt;policyEntry queue="TEST.&gt;" enableAudit="false"&gt;
            &lt;conditionalNetworkBridgeFilterFactory replayWhenNoConsumers="true"/&gt;
          &lt;/policyEntry&gt;
        &lt;/policyEntries&gt;
      &lt;/policyMap&gt;
    &lt;/destinationPolicy&gt;</pre>
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<p>Also, take a look at <a shape="rect" class="external-link" href="http://svn.apache.org/viewvc/activemq/trunk/activemq-unit-tests/src/test/java/org/apache/activemq/usecases/VirtualTopicNetworkClusterReactivationTest.java?view=markup">this unit test to see the full configuration and usage</a></p></div>