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| 771 | blopes | 1 | <!DOCTYPE html SYSTEM "about:legacy-compat"> |
| 2 | <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 9 Configuration Reference (9.0.112) - The Cluster object</title></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 9 Configuration Reference</h1><div class="versionInfo"> |
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| 3 | Version 9.0.112, |
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| 4 | <time datetime="2025-11-06">Nov 6 2025</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://cwiki.apache.org/confluence/display/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="runtime-attributes.html">Runtime attributes</a></li><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 object</h2><h3 id="Table_of_Contents">Table of Contents</h3><div class="text"> |
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| 5 | <ul><li><a href="#Introduction">Introduction</a></li><li><a href="#Security">Security</a></li><li><a href="#Engine_vs_Host_placement">Engine vs Host placement</a></li><li><a href="#Context_Attribute_Replication">Context Attribute Replication</a></li><li><a href="#Nested_Components">Nested Components</a></li><li><a href="#Attributes">Attributes</a><ol><li><a href="#SimpleTcpCluster_Attributes">SimpleTcpCluster Attributes</a></li></ol></li></ul> |
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| 6 | </div><h3 id="Introduction">Introduction</h3><div class="text"> |
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| 7 | <p> |
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| 8 | The tomcat cluster implementation provides session replication, context attribute replication and |
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| 9 | cluster wide WAR file deployment. |
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| 10 | While the <code>Cluster</code> configuration is fairly complex, the default configuration will work |
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| 11 | for most people out of the box. </p><p> |
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| 12 | The Tomcat Cluster implementation is very extensible, and hence we have exposed a myriad of options, |
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| 13 | making the configuration seem like a lot, but don't lose faith, instead you have a tremendous control |
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| 14 | over what is going on.</p> |
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| 15 | </div><h3 id="Security">Security</h3><div class="text"> |
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| 16 | |||
| 17 | <p>The cluster implementation is written on the basis that a secure, trusted |
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| 18 | network is used for all of the cluster related network traffic. It is not safe |
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| 19 | to run a cluster on a insecure, untrusted network.</p> |
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| 20 | |||
| 21 | <p>There are many options for providing a secure, trusted network for use by a |
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| 22 | Tomcat cluster. These include:</p> |
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| 23 | <ul> |
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| 24 | <li>private LAN</li> |
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| 25 | <li>a Virtual Private Network (VPN)</li> |
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| 26 | <li>IPSEC</li> |
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| 27 | </ul> |
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| 28 | |||
| 29 | <p>The <a href="cluster-interceptor.html#org.apache.catalina.tribes.group.interceptors.EncryptInterceptor_Attributes">EncryptInterceptor</a> |
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| 30 | provides confidentiality and integrity protection but it does not protect |
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| 31 | against all risks associated with running a Tomcat cluster on an untrusted |
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| 32 | network, particularly DoS attacks.</p> |
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| 33 | |||
| 34 | </div><h3 id="Engine_vs_Host_placement">Engine vs Host placement</h3><div class="text"> |
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| 35 | <p> |
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| 36 | You can place the <code><Cluster></code> element inside either the <code><Engine></code> |
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| 37 | container or the <code><Host></code> container.<br> |
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| 38 | Placing it in the engine, means that you will support clustering in all virtual hosts of Tomcat, |
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| 39 | and share the messaging component. When you place the <code><Cluster></code> inside the <code><Engine></code> |
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| 40 | element, the cluster will append the host name of each session manager to the managers name so that two contexts with |
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| 41 | the same name but sitting inside two different hosts will be distinguishable. |
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| 42 | </p> |
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| 43 | </div><h3 id="Context_Attribute_Replication">Context Attribute Replication</h3><div class="text"> |
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| 44 | <p>To configure context attribute replication, simply do this by swapping out the context implementation |
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| 45 | used for your application context.</p> |
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| 46 | <div class="codeBox"><pre><code><Context className="org.apache.catalina.ha.context.ReplicatedContext"/></code></pre></div> |
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| 47 | <p> |
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| 48 | This context extends the Tomcat <code><a href="context.html">StandardContext</a></code> |
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| 49 | so all the options from the <a href="context.html">base implementation</a> are valid. |
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| 50 | </p> |
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| 51 | </div><h3 id="Nested_Components">Nested Components</h3><div class="text"> |
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| 52 | <p><b><a href="cluster-manager.html">Manager</a>:</b> <br> |
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| 53 | The session manager element identifies what kind of session manager is used in this cluster implementation. |
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| 54 | This manager configuration is identical to the one you would use in a regular <code><a href="context.html#Nested_Components"><Context></a></code> configuration. |
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| 55 | <br>The default value is the <code>org.apache.catalina.ha.session.DeltaManager</code> that is closely coupled with |
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| 56 | the <code>SimpleTcpCluster</code> implementation. Other managers like the <code>org.apache.catalina.ha.session.BackupManager</code> |
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| 57 | are/could be loosely coupled and don't rely on the <code>SimpleTcpCluster</code> for its data replication. |
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| 58 | </p> |
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| 59 | <p><b><a href="cluster-channel.html">Channel</a>:</b> <br> |
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| 60 | The Channel and its sub components are all part of the IO layer |
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| 61 | for the cluster group, and is a module in it's own that we have nick named "Tribes" |
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| 62 | <br> |
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| 63 | Any configuring and tuning of the network layer, the messaging and the membership logic |
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| 64 | will be done in the channel and its nested components. |
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| 65 | You can always find out more about <a href="../tribes/introduction.html">Apache Tribes</a> |
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| 66 | </p> |
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| 67 | <p><b><a href="cluster-valve.html">Valve</a>:</b> <br> |
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| 68 | The Tomcat Cluster implementation uses <code>Tomcat <a href="valve.html">Valves</a></code> to |
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| 69 | track when requests enter and exit the servlet container. It uses these valves to be able to make |
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| 70 | intelligent decisions on when to replicate data, which is always at the end of a request. |
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| 71 | </p> |
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| 72 | <p><b><a href="cluster-deployer.html">Deployer</a>:</b> <br> |
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| 73 | The Deployer component is the Tomcat Farm Deployer. It allows you to deploy and undeploy applications |
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| 74 | cluster wide. |
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| 75 | </p> |
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| 76 | <p><b><a href="cluster-listener.html">ClusterListener</a>:</b> <br> |
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| 77 | ClusterListener's are used to track messages sent and received using the <code>SimpleTcpCluster</code>. |
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| 78 | If you wish to track messages, you can add a listener here, or you can add a valve to the channel object. |
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| 79 | </p> |
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| 80 | </div><h3 id="Attributes">Attributes</h3><div class="text"> |
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| 81 | <div class="subsection"><h4 id="SimpleTcpCluster_Attributes">SimpleTcpCluster Attributes</h4><div class="text"> |
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| 82 | <table class="defaultTable"><tr><th style="width: 15%;"> |
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| 83 | Attribute |
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| 84 | </th><th style="width: 85%;"> |
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| 85 | Description |
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| 86 | </th></tr><tr id="Attributes_SimpleTcpCluster Attributes_className"><td><strong><code class="attributeName">className</code></strong></td><td> |
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| 87 | <p>The main cluster class, currently only one is available, |
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| 88 | <code>org.apache.catalina.ha.tcp.SimpleTcpCluster</code> |
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| 89 | </p> |
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| 90 | </td></tr><tr id="Attributes_SimpleTcpCluster Attributes_channelSendOptions"><td><strong><code class="attributeName">channelSendOptions</code></strong></td><td> |
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| 91 | <p>The Tribes channel send options, default is <code>8</code>.<br> |
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| 92 | This option is used to set the flag that all messages sent through the |
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| 93 | SimpleTcpCluster uses. The flag decides how the messages are sent, and is a simple logical OR.</p> |
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| 94 | |||
| 95 | <div class="codeBox"><pre><code>int options = Channel.SEND_OPTIONS_ASYNCHRONOUS | |
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| 96 | Channel.SEND_OPTIONS_SYNCHRONIZED_ACK | |
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| 97 | Channel.SEND_OPTIONS_USE_ACK;</code></pre></div> |
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| 98 | <p>Some of the values are:<br> |
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| 99 | <code>Channel.SEND_OPTIONS_SYNCHRONIZED_ACK = 0x0004</code><br> |
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| 100 | <code>Channel.SEND_OPTIONS_ASYNCHRONOUS = 0x0008</code><br> |
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| 101 | <code>Channel.SEND_OPTIONS_USE_ACK = 0x0002</code><br> |
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| 102 | So to use ACK and ASYNC messaging, the flag would be <code>10</code> (8+2) |
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| 103 | <br> |
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| 104 | Note that if you use ASYNC messaging it is possible for update messages |
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| 105 | for a session to be processed by the receiving nodes in a different order |
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| 106 | to the order in which they were sent. |
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| 107 | </p> |
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| 108 | <p> |
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| 109 | The various <code>channelSendOptions</code> values offer a tradeoff |
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| 110 | between throughput on the sending node and the reliability of |
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| 111 | replication should the sending or receiving node(s) fail. Here are |
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| 112 | some common options. "Message" could be any message sent between nodes, |
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| 113 | but only session-change messages are considered, here. |
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| 114 | </p> |
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| 115 | <p> |
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| 116 | <code>channelSendOptions="8"</code> / <code>channelSendOptions="async"</code> |
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| 117 | As far as the sender is concerned, the message is "sent" |
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| 118 | as soon as it has been placed in the queue on the sender for |
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| 119 | transmission to the other nodes. The message may not reach any or all |
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| 120 | of the recipient nodes and may not be successfully processed on any |
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| 121 | nodes that it does reach. This option offers the highest throughput on |
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| 122 | the sender but the least reliability, as the triggering request will |
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| 123 | complete without any knowledge of the success/failure of the session |
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| 124 | replication. |
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| 125 | </p> |
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| 126 | <p> |
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| 127 | <code>channelSendOptions="2"</code> / <code>channelSendOptions="use_ack"</code> |
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| 128 | The sender will block the completion of the current request until all |
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| 129 | of the receiving nodes have acknowledged that they have received the |
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| 130 | message, but have not necessarily processed that message. This option |
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| 131 | will result in lower throughput on the sending node, because the message |
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| 132 | must be transmitted and the acknowledgement received, but the |
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| 133 | reliability is greater than the asynchronous model. |
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| 134 | </p> |
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| 135 | <p> |
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| 136 | <code>channelSendOptions="6"</code> / <code>channelSendOptions="sync,use_ack"</code> |
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| 137 | The sender will block the completion of the current request until |
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| 138 | all of the receiving nodes have acknowledged that they have received |
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| 139 | <u>and</u> processed the message. This option will have the lowest |
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| 140 | throughput (of these three) but the greatest reliability. |
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| 141 | </p> |
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| 142 | <p> |
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| 143 | You may also set these options as a comma separated string, e.g. "async, multicast", which |
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| 144 | will be translated into <code>Channel.SEND_OPTIONS_ASYNCHRONOUS | Channel.SEND_OPTIONS_MULTICAST</code> |
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| 145 | <br> |
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| 146 | The valid option names are "asynchronous" (alias "async"), "byte_message" (alias "byte") |
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| 147 | , "multicast", "secure", "synchronized_ack" (alias "sync"), "udp", "use_ack" |
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| 148 | </p> |
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| 149 | </td></tr><tr id="Attributes_SimpleTcpCluster Attributes_channelStartOptions"><td><code class="attributeName">channelStartOptions</code></td><td> |
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| 150 | <p>Sets the start and stop flags for the <Channel> object used by the cluster. |
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| 151 | The default is <code>Channel.DEFAULT</code> which starts all the channel services, such as |
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| 152 | sender, receiver, membership sender and membership receiver. |
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| 153 | The following flags are available today:</p> |
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| 154 | <div class="codeBox"><pre><code>Channel.DEFAULT = Channel.SND_RX_SEQ (1) | |
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| 155 | Channel.SND_TX_SEQ (2) | |
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| 156 | Channel.MBR_RX_SEQ (4) | |
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| 157 | Channel.MBR_TX_SEQ (8);</code></pre></div> |
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| 158 | <p>When using the static membership service |
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| 159 | <code>org.apache.catalina.tribes.membership.StaticMembershipService</code> |
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| 160 | you must ensure that this attribute is configured to use the default |
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| 161 | value.</p> |
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| 162 | </td></tr><tr id="Attributes_SimpleTcpCluster Attributes_heartbeatBackgroundEnabled"><td><code class="attributeName">heartbeatBackgroundEnabled</code></td><td> |
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| 163 | <p>Flag whether invoke channel heartbeat at container background thread. Default value is false. |
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| 164 | Enable this flag don't forget to disable the channel heartbeat thread. |
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| 165 | </p> |
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| 166 | </td></tr><tr id="Attributes_SimpleTcpCluster Attributes_notifyLifecycleListenerOnFailure"><td><code class="attributeName">notifyLifecycleListenerOnFailure</code></td><td> |
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| 167 | <p>Flag whether notify LifecycleListeners if all ClusterListener couldn't accept channel message. |
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| 168 | Default value is false. |
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| 169 | </p> |
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| 170 | </td></tr></table> |
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| 171 | </div></div> |
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| 172 | </div></div></div></div></div><footer><div id="footer"> |
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| 173 | Copyright © 1999-2025, The Apache Software Foundation |
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| 174 | <br> |
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| 175 | Apache Tomcat, Tomcat, Apache, the Apache Tomcat logo and the Apache logo |
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| 176 | are either registered trademarks or trademarks of the Apache Software |
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| 177 | Foundation. |
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| 178 | </div></footer></div></body></html> |