149 lines
6.2 KiB
HTML
149 lines
6.2 KiB
HTML
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<html>
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<head>
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<title>ActiveMQ Artemis JMS Failover With Transaction using Replication Example</title>
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<link rel="stylesheet" type="text/css" href="../../../common/common.css" />
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<link rel="stylesheet" type="text/css" href="../../../common/prettify.css" />
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<script type="text/javascript" src="../../../common/prettify.js"></script>
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</head>
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<body onload="prettyPrint()">
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<h1>JMS Failover With Transaction using Replication Example</h1>
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<p>This example demonstrates two servers coupled as a live-backup pair for high availability (HA) using replication, and a client
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connection failing over from live to backup when the live server is crashed.</p>
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<p>Failover behavior differs whether the JMS session is transacter or not.</p>
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<p>When a <em>transacted</em> JMS session is used, once-and-only once delivery is guaranteed.</p>
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<ul>
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<li>if the failover occurs while there is an in-flight transaction, the transaction will be flagged as <em>rollback only</em>. In that case, the JMS client
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will need to retry the transaction work.</li>
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<li>if the failover occurs while there is <em>no</em> in-flight transaction, the failover will be transparent to the user.</li>
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</ul>
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<p>ActiveMQ Artemis also provides an example for <a href="../non-transactional-failover/readme.html">non-transaction failover</a>.</p>
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<p>For more information on ActiveMQ Artemis failover and HA, and clustering in general, please see the clustering
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section of the user manual.</p>
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<h2>Example step-by-step</h2>
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<p><i>To run the example, simply type <code>mvn verify -Pexample</code> from this directory</i></p>
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<p>In this example, the live server is server 1, and the backup server is server 0</p>
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<p>The connection will initially be created to server1, server 1 will crash, and the client will carry on
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seamlessly on server 0, the backup server.</p>
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<ol>
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<li>Get an initial context for looking up JNDI from server #1.</li>
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<pre class="prettyprint">
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initialContext = getContext(1);
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</pre>
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<li>Look up the JMS resources from JNDI on server #1.</li>
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<pre class="prettyprint">
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Queue queue = (Queue)initialContext.lookup("/queue/exampleQueue");
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ConnectionFactory connectionFactory = (ConnectionFactory)initialContext.lookup("/ConnectionFactory");
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</pre>
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<li>Create a JMS Connection</li>
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<pre class="prettyprint">
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connection = connectionFactory.createConnection();
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</pre>
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<li>Create a JMS <em>transacted</em> Session</li>
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<pre class="prettyprint">
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Session session = connection.createSession(true, 0);
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</pre>
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<li>Start the connection to ensure delivery occurs</li>
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<pre class="prettyprint">
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connection.start();
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</pre>
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<li>Create a JMS MessageProducer</li>
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<pre class="prettyprint">
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MessageProducer producer = session.createProducer(queue);
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</pre>
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<li>Create a JMS MessageConsumer</li>
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<pre class="prettyprint">
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MessageConsumer consumer = session.createConsumer(queue);
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</pre>
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<li>Send half of the messages, kill the live server and send the remaining messages</li>
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<pre class="prettyprint">
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sendMessages(session, producer, numMessages, true);
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</pre>
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<p>When server #1 crashes, the client automatically detects the failure and automatically
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fails over from server #1 to server #0 (in your real program you wouldn't need to sleep).
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</p>
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<li>As failover occurred during transaction, the session has been marked for <em>rollback only</em> and commit will fail</li>
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<pre class="prettyprint">
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try
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{
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session.commit();
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} catch (TransactionRolledBackException e)
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{
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System.err.println("transaction has been rolled back: " + e.getMessage());
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}
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</pre>
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<li>We resend all the messages</li>
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<pre class="prettyprint">
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sendMessages(session, producer, numMessages, false);
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</pre>
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<li>We commit the session successfully: the messages will be all delivered to the activated backup server</li>
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<pre class="prettyprint">
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session.commit();
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</pre>
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<li>We are now transparently reconnected to server #0, the backup server.
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We consume the messages sent before the crash of the live server, commit the session, and check there are no other message on the queue</li>
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<pre class="prettyprint">
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for (int i = 0; i < numMessages; i++)
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{
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TextMessage message0 = (TextMessage)consumer.receive(5000);
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System.out.println("Got message: " + message0.getText());
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}
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session.commit();
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System.out.println("Other message on the server? " + consumer.receive(5000));
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</pre>
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<li>And finally, <strong>always</strong> remember to close your resources after use, in a <code>finally</code> block. Closing a JMS connection will automatically close all of its sessions, consumers, producer and browser objects</li>
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<pre class="prettyprint">
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finally
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{
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if (connection != null)
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{
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connection.close();
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}
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if (initialContext != null)
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{
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initialContext.close();
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}
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}
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</pre>
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</ol>
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</body>
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</html>
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