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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 (8.0.53) - The Cluster Membership object</title><meta name="author" content="Filip Hanik"><script type="application/javascript" data-comments-identifier="tomcat-8.0-doc/config/cluster-membership">
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</script></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 8.0.53,
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<time datetime="2018-06-29">Jun 29 2018</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</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></ul></div></nav></div></div><div id="mainRight"><div id="content"><h2>The Cluster Membership 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="#Default_Implementation">Default Implementation</a></li><li><a href="#Attributes">Attributes</a><ol><li><a href="#Multicast_Attributes">Multicast Attributes</a></li></ol></li></ul>
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</div><h3 id="Introduction">Introduction</h3><div class="text">
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<p>
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The membership component in the Apache Tribes <a href="cluster-channel.html">Channel</a> is responsible
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for dynamic discovery of other members(nodes) in the cluster.
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</p>
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</div><h3 id="Default_Implementation">Default Implementation</h3><div class="text">
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<p>
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The default implementation of the cluster group notification is built on top of multicast heartbeats
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sent using UDP packets to a multicast IP address.
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Cluster members are grouped together by using the same multicast address/port combination.
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Each member sends out a heartbeat with a given interval (<code>frequency</code>), and this
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heartbeat is used for dynamic discovery.
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In a similar fashion, if a heartbeat has not been received in a timeframe specified by <code>dropTime</code>
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ms. a member is considered suspect and the channel and any membership listener will be notified.
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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="Multicast_Attributes">Multicast 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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<p>
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The default value is <code>org.apache.catalina.tribes.membership.McastService</code>
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and is currently the only implementation.
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This implementation uses multicast heartbeats for member discovery.
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</p>
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</td></tr><tr><td><code class="attributeName">address</code></td><td>
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<p>
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The multicast address that the membership will broadcast its presence and listen
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for other heartbeats on. The default value is <code>228.0.0.4</code>
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Make sure your network is enabled for multicast traffic.<br>
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The multicast address, in conjunction with the <code>port</code> is what
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creates a cluster group. To divide up your farm into several different group, or to
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split up QA from production, change the <code>port</code> or the <code>address</code>
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<br>Previously known as mcastAddr.
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</p>
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</td></tr><tr><td><code class="attributeName">port</code></td><td>
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<p>
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The multicast port, the default value is <code>45564</code><br>
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The multicast port, in conjunction with the <code>address</code> is what
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creates a cluster group. To divide up your farm into several different group, or to
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split up QA from production, change the <code>port</code> or the <code>address</code>
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</p>
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</td></tr><tr><td><code class="attributeName">frequency</code></td><td>
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<p>
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The frequency in milliseconds in which heartbeats are sent out. The default value is <code>500</code> ms.<br>
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In most cases the default value is sufficient. Changing this value, simply changes the interval in between heartbeats.
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</p>
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</td></tr><tr><td><code class="attributeName">dropTime</code></td><td>
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<p>
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The membership component will time out members and notify the Channel if a member fails to send a heartbeat within
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a give time. The default value is <code>3000</code> ms. This means, that if a heartbeat is not received from a
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member in that timeframe, the membership component will notify the cluster of this.<br>
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On a high latency network you may wish to increase this value, to protect against false positives.<br>
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Apache Tribes also provides a <a href="cluster-interceptor.html#org.apache.catalina.tribes.group.interceptors.TcpFailureDetector_Attributes"><code>TcpFailureDetector</code></a> that will
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verify a timeout using a TCP connection when a heartbeat timeout has occurred. This protects against false positives.
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</p>
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</td></tr><tr><td><code class="attributeName">bind</code></td><td>
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<p>
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Use this attribute if you wish to bind your multicast traffic to a specific network interface.
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By default, or when this attribute is unset, it tries to bind to <code>0.0.0.0</code> and sometimes on multihomed hosts
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this becomes a problem.
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</p>
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</td></tr><tr><td><code class="attributeName">ttl</code></td><td>
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<p>
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The time-to-live setting for the multicast heartbeats.
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This setting should be a value between 0 and 255. The default value is VM implementation specific.
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</p>
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</td></tr><tr><td><code class="attributeName">domain</code></td><td>
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<p>
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Apache Tribes has the ability to logically group members into domains, by using this domain attribute.
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The <code>org.apache.catalina.tribes.Member.getDomain()</code> method returns the value specified here.
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</p>
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</td></tr><tr><td><code class="attributeName">soTimeout</code></td><td>
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<p>
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The sending and receiving of heartbeats is done on a single thread, hence to avoid blocking this thread forever,
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you can control the <code>SO_TIMEOUT</code> value on this socket.<br>
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If a value smaller or equal to 0 is presented, the code will default this value to frequency
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</p>
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</td></tr><tr><td><code class="attributeName">recoveryEnabled</code></td><td>
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<p>
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In case of a network failure, Java multicast socket don't transparently fail over, instead the socket will continuously
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throw IOException upon each receive request. When recoveryEnabled is set to true, this will close the multicast socket
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and open a new socket with the same properties as defined above.<br>
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The default is <code>true</code>. <br>
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</p>
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</td></tr><tr><td><code class="attributeName">recoveryCounter</code></td><td>
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<p>
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When <code>recoveryEnabled==true</code> this value indicates how many
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times an error has to occur before recovery is attempted. The default is
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<code>10</code>. <br>
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</p>
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</td></tr><tr><td><code class="attributeName">recoverySleepTime</code></td><td>
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<p>
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When <code>recoveryEnabled==true</code> this value indicates how long time (in milliseconds)
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the system will sleep in between recovery attempts, until it recovers successfully.
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The default is <code>5000</code> (5 seconds). <br>
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</p>
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</td></tr><tr><td><code class="attributeName">localLoopbackDisabled</code></td><td>
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<p>
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Membership uses multicast, it will call <code>java.net.MulticastSocket.setLoopbackMode(localLoopbackDisabled)</code>.
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When <code>localLoopbackDisabled==true</code> multicast messages will not reach other nodes on the same local machine.
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The default is <code>false</code>. <br>
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</p>
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</td></tr></table>
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</div></div>
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</div><div class="noprint"><h3 id="comments_section">
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Comments
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</h3><div class="text"><p class="notice"><strong>Notice: </strong>This comments section collects your suggestions
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on improving documentation for Apache Tomcat.<br><br>
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If you have trouble and need help, read
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and ask your question on the tomcat-users
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