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<html lang="en"><head><META http-equiv="Content-Type" content="text/html; charset=UTF-8"><link href="../images/docs-stylesheet.css" rel="stylesheet" type="text/css"><title>Apache Tomcat 8 Configuration Reference (8.5.73) - The Cluster Channel object</title><meta name="author" content="Filip Hanik"></head><body><div id="wrapper"><header><div id="header"><div><div><div class="logo noPrint"><a href="https://tomcat.apache.org/"><img alt="Tomcat Home" src="../images/tomcat.png"></a></div><div style="height: 1px;"></div><div class="asfLogo noPrint"><a href="https://www.apache.org/" target="_blank"><img src="../images/asf-logo.svg" alt="The Apache Software Foundation" style="width: 266px; height: 83px;"></a></div><h1>Apache Tomcat 8 Configuration Reference</h1><div class="versionInfo">
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Version 8.5.73,
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<time datetime="2021-11-11">Nov 11 2021</time></div><div style="height: 1px;"></div><div style="clear: left;"></div></div></div></div></header><div id="middle"><div><div id="mainLeft" class="noprint"><div><nav><div><h2>Links</h2><ul><li><a href="../index.html">Docs Home</a></li><li><a href="index.html">Config Ref. Home</a></li><li><a href="https://wiki.apache.org/tomcat/FAQ">FAQ</a></li><li><a href="#comments_section">User Comments</a></li></ul></div><div><h2>Top Level Elements</h2><ul><li><a href="server.html">Server</a></li><li><a href="service.html">Service</a></li></ul></div><div><h2>Executors</h2><ul><li><a href="executor.html">Executor</a></li></ul></div><div><h2>Connectors</h2><ul><li><a href="http.html">HTTP/1.1</a></li><li><a href="http2.html">HTTP/2</a></li><li><a href="ajp.html">AJP</a></li></ul></div><div><h2>Containers</h2><ul><li><a href="context.html">Context</a></li><li><a href="engine.html">Engine</a></li><li><a href="host.html">Host</a></li><li><a href="cluster.html">Cluster</a></li></ul></div><div><h2>Nested Components</h2><ul><li><a href="cookie-processor.html">CookieProcessor</a></li><li><a href="credentialhandler.html">CredentialHandler</a></li><li><a href="globalresources.html">Global Resources</a></li><li><a href="jar-scanner.html">JarScanner</a></li><li><a href="jar-scan-filter.html">JarScanFilter</a></li><li><a href="listeners.html">Listeners</a></li><li><a href="loader.html">Loader</a></li><li><a href="manager.html">Manager</a></li><li><a href="realm.html">Realm</a></li><li><a href="resources.html">Resources</a></li><li><a href="sessionidgenerator.html">SessionIdGenerator</a></li><li><a href="valve.html">Valve</a></li></ul></div><div><h2>Cluster Elements</h2><ul><li><a href="cluster.html">Cluster</a></li><li><a href="cluster-manager.html">Manager</a></li><li><a href="cluster-channel.html">Channel</a></li><li><a href="cluster-membership.html">Channel/Membership</a></li><li><a href="cluster-sender.html">Channel/Sender</a></li><li><a href="cluster-receiver.html">Channel/Receiver</a></li><li><a href="cluster-interceptor.html">Channel/Interceptor</a></li><li><a href="cluster-valve.html">Valve</a></li><li><a href="cluster-deployer.html">Deployer</a></li><li><a href="cluster-listener.html">ClusterListener</a></li></ul></div><div><h2>web.xml</h2><ul><li><a href="filter.html">Filter</a></li></ul></div><div><h2>Other</h2><ul><li><a href="systemprops.html">System properties</a></li><li><a href="jaspic.html">JASPIC</a></li></ul></div></nav></div></div><div id="mainRight"><div id="content"><h2>The Cluster Channel object</h2><h3 id="Table_of_Contents">Table of Contents</h3><div class="text">
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<ul><li><a href="#Introduction">Introduction</a></li><li><a href="#Nested_Components">Nested Components</a></li><li><a href="#Attributes">Attributes</a><ol><li><a href="#Common_Attributes">Common Attributes</a></li><li><a href="#org.apache.catalina.tribes.group.GroupChannel_Attributes">org.apache.catalina.tribes.group.GroupChannel Attributes</a></li></ol></li></ul>
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</div><h3 id="Introduction">Introduction</h3><div class="text">
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The cluster channel is the main component of a small framework we've nicknamed Apache Tribes.<br>
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The channel manages a set of sub components and together they create a group communication framework.<br>
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This framework is then used internally by the components that need to send messages between different Tomcat instances.
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<br>
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A few examples of these components would be the SimpleTcpCluster that does the messaging for the DeltaManager,
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or the BackupManager that uses a different replication strategy. The ReplicatedContext object does also
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use the channel object to communicate context attribute changes.
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</div><h3 id="Nested_Components">Nested Components</h3><div class="text">
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<p><b><a href="cluster-membership.html">Channel/Membership</a>:</b> <br>
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The Membership component is responsible for auto discovering new nodes in the cluster
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and also to provide for notifications for any nodes that have not responded with a heartbeat.
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The default implementation uses multicast.<br>
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In the membership component you configure how your nodes, aka. members, are to be discovered and/or
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divided up.
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You can always find out more about <a href="../tribes/introduction.html">Apache Tribes</a>
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</p>
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<p><b><a href="cluster-sender.html">Channel/Sender</a>:</b> <br>
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The Sender component manages all outbound connections and data messages that are sent
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over the network from one node to another.
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This component allows messages to be sent in parallel.
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The default implementation uses TCP client sockets, and socket tuning for outgoing messages are
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configured here.<br>
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You can always find out more about <a href="../tribes/introduction.html">Apache Tribes</a>
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</p>
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<p><b><a href="cluster-sender.html#transport">Channel/Sender/Transport</a>:</b> <br>
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The Transport component is the bottom IO layer for the sender component.
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The default implementation uses non-blocking TCP client sockets.<br>
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You can always find out more about <a href="../tribes/introduction.html">Apache Tribes</a>
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</p>
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<p><b><a href="cluster-receiver.html">Channel/Receiver</a>:</b> <br>
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The receiver component listens for messages from other nodes.
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Here you will configure the cluster thread pool, as it will dispatch incoming
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messages to a thread pool for faster processing.
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The default implementation uses non-blocking TCP server sockets.<br>
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You can always find out more about <a href="../tribes/introduction.html">Apache Tribes</a>
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</p>
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<p><b><a href="cluster-interceptor.html">Channel/Interceptor</a>:</b> <br>
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The channel will send messages through an interceptor stack. Because of this, you have the ability to
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customize the way messages are sent and received, and even how membership is handled.<br>
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You can always find out more about <a href="../tribes/introduction.html">Apache Tribes</a>
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</p>
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</div><h3 id="Attributes">Attributes</h3><div class="text">
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<div class="subsection"><h4 id="Common_Attributes">Common Attributes</h4><div class="text">
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<table class="defaultTable"><tr><th style="width: 15%;">
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Attribute
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</th><th style="width: 85%;">
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Description
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</th></tr><tr><td><strong><code class="attributeName">className</code></strong></td><td>
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The default value here is <code>org.apache.catalina.tribes.group.GroupChannel</code> and is
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currently the only implementation available.
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</td></tr></table>
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</div></div>
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<div class="subsection"><h4 id="org.apache.catalina.tribes.group.GroupChannel_Attributes">org.apache.catalina.tribes.group.GroupChannel Attributes</h4><div class="text">
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<table class="defaultTable"><tr><th style="width: 15%;">
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Attribute
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</th><th style="width: 85%;">
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Description
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</th></tr><tr><td><code class="attributeName">heartbeat</code></td><td>
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Flag whether the channel manages its own heartbeat.
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If set to true, the channel start a local thread for the heart beat.
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If set this flag to false, you must set SimpleTcpCluster#heartbeatBackgroundEnabled
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to true. default value is true.
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</td></tr><tr><td><code class="attributeName">heartbeatSleeptime</code></td><td>
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If heartbeat == true, specifies the interval of heartbeat thread in milliseconds.
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The default is 5000 (5 seconds).
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</td></tr><tr><td><code class="attributeName">optionCheck</code></td><td>
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If set to true, the GroupChannel will check the option flags that each
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interceptor is using. Reports an error if two interceptor share the same
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flag. The default is false.
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</td></tr><tr><td><code class="attributeName">jmxEnabled</code></td><td>
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Flag whether the channel components register with JMX or not.
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The default value is true.
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</td></tr><tr><td><code class="attributeName">jmxDomain</code></td><td>
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if <code>jmxEnabled</code> set to true, specifies the jmx domain which
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this channel should be registered. The ClusterChannel is used as the
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default value.
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</td></tr><tr><td><code class="attributeName">jmxPrefix</code></td><td>
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if <code>jmxEnabled</code> set to true, specifies the jmx prefix which
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will be used with channel ObjectName.
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</td></tr></table>
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