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| <!DOCTYPE document [ |
| <!ENTITY project SYSTEM "project.xml"> |
| ]> |
| <document url="cluster.html"> |
| |
| &project; |
| |
| <properties> |
| <author email="fhanik@apache.org">Filip Hanik</author> |
| <title>The Cluster object</title> |
| </properties> |
| |
| <body> |
| |
| <section name="Table of Contents"> |
| <toc/> |
| </section> |
| |
| <section name="Introduction"> |
| <p> |
| The tomcat cluster implementation provides session replication, context attribute replication and |
| cluster wide WAR file deployment. |
| While the <code>Cluster</code> configuration is fairly complex, the default configuration will work |
| for most people out of the box. </p><p> |
| The Tomcat Cluster implementation is very extensible, and hence we have exposed a myriad of options, |
| making the configuration seem like a lot, but don't lose faith, instead you have a tremendous control |
| over what is going on.</p> |
| </section> |
| <section name="Security"> |
| |
| <p>The cluster implementation is written on the basis that a secure, trusted |
| network is used for all of the cluster related network traffic. It is not safe |
| to run a cluster on a insecure, untrusted network.</p> |
| |
| <p>There are many options for providing a secure, trusted network for use by a |
| Tomcat cluster. These include:</p> |
| <ul> |
| <li>private LAN</li> |
| <li>a Virtual Private Network (VPN)</li> |
| <li>IPSEC</li> |
| </ul> |
| |
| </section> |
| <section name="Engine vs Host placement"> |
| <p> |
| You can place the <code><Cluster></code> element inside either the <code><Engine></code> |
| container or the <code><Host></code> container.<br/> |
| Placing it in the engine, means that you will support clustering in all virtual hosts of Tomcat, |
| and share the messaging component. When you place the <code><Cluster></code> inside the <code><Engine></code> |
| element, the cluster will append the host name of each session manager to the managers name so that two contexts with |
| the same name but sitting inside two different hosts will be distinguishable. |
| </p> |
| </section> |
| <section name="Context Attribute Replication"> |
| <p>To configure context attribute replication, simply do this by swapping out the context implementation |
| used for your application context.</p> |
| <source><Context className="org.apache.catalina.ha.context.ReplicatedContext"/></source> |
| <p> |
| This context extends the Tomcat <code><a href="context.html">StandardContext</a></code> |
| so all the options from the <a href="context.html">base implementation</a> are valid. |
| </p> |
| </section> |
| <section name="Nested Components"> |
| <p><b><a href="cluster-manager.html">Manager</a>:</b> <br/> |
| The session manager element identifies what kind of session manager is used in this cluster implementation. |
| 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. |
| <br/>The default value is the <code>org.apache.catalina.ha.session.DeltaManager</code> that is closely coupled with |
| the <code>SimpleTcpCluster</code> implementation. Other managers like the <code>org.apache.catalina.ha.session.BackupManager</code> |
| are/could be loosely coupled and don't rely on the <code>SimpleTcpCluster</code> for its data replication. |
| </p> |
| <p><b><a href="cluster-channel.html">Channel</a>:</b> <br/> |
| The Channel and its sub components are all part of the IO layer |
| for the cluster group, and is a module in it's own that we have nick named "Tribes" |
| <br/> |
| Any configuring and tuning of the network layer, the messaging and the membership logic |
| will be done in the channel and its nested components. |
| You can always find out more about <a href="../tribes/introduction.html">Apache Tribes</a> |
| </p> |
| <p><b><a href="cluster-valve.html">Valve</a>:</b> <br/> |
| The Tomcat Cluster implementation uses <code>Tomcat <a href="valve.html">Valves</a></code> to |
| track when requests enter and exit the servlet container. It uses these valves to be able to make |
| intelligent decisions on when to replicate data, which is always at the end of a request. |
| </p> |
| <p><b><a href="cluster-deployer.html">Deployer</a>:</b> <br/> |
| The Deployer component is the Tomcat Farm Deployer. It allows you to deploy and undeploy applications |
| cluster wide. |
| </p> |
| <p><b><a href="cluster-listener.html">ClusterListener</a>:</b> <br/> |
| ClusterListener's are used to track messages sent and received using the <code>SimpleTcpCluster</code>. |
| If you wish to track messages, you can add a listener here, or you can add a valve to the channel object. |
| </p> |
| </section> |
| |
| <section name="Deprecated configuration options"> |
| <p> |
| <b>Deprecated settings:</b> In the previous version of Tomcat you were able to control session |
| manager settings using manager.<property>=value. |
| This has been discontinued, as the way it was written interferes with |
| the ability to support multiple different manager classes under one cluster implementation, |
| as the same properties might have the different effect on different managers. |
| </p> |
| </section> |
| |
| <section name="Attributes"> |
| <subsection name="SimpleTcpCluster Attributes"> |
| <attributes> |
| <attribute name="className" required="true"> |
| <p>The main cluster class, currently only one is available, |
| <code>org.apache.catalina.ha.tcp.SimpleTcpCluster</code> |
| </p> |
| </attribute> |
| <attribute name="channelSendOptions" required="true"> |
| <p>The Tribes channel send options, default is <code>8</code>.<br/> |
| This option is used to set the flag that all messages sent through the |
| SimpleTcpCluster uses. The flag decides how the messages are sent, and is a simple logical OR.</p> |
| |
| <source>int options = Channel.SEND_OPTIONS_ASYNCHRONOUS | |
| Channel.SEND_OPTIONS_SYNCHRONIZED_ACK | |
| Channel.SEND_OPTIONS_USE_ACK;</source> |
| <p>Some of the values are:<br/> |
| <code>Channel.SEND_OPTIONS_SYNCHRONIZED_ACK = 0x0004</code><br/> |
| <code>Channel.SEND_OPTIONS_ASYNCHRONOUS = 0x0008</code><br/> |
| <code>Channel.SEND_OPTIONS_USE_ACK = 0x0002</code><br/> |
| So to use ACK and ASYNC messaging, the flag would be <code>10</code> (8+2) |
| <br/> |
| Note that if you use ASYNC messaging it is possible for update messages |
| for a session to be processed by the receiving nodes in a different order |
| to the order in which they were sent.</p> |
| </attribute> |
| <attribute name="channelStartOptions" required="false"> |
| <p>Sets the start and stop flags for the <Channel> object used by the cluster. |
| The default is <code>Channel.DEFAULT</code> which starts all the channel services, such as |
| sender, receiver, multicast sender and multicast receiver. |
| The following flags are available today:</p> |
| <source>Channel.DEFAULT = Channel.SND_RX_SEQ (1) | |
| Channel.SND_TX_SEQ (2) | |
| Channel.MBR_RX_SEQ (4) | |
| Channel.MBR_TX_SEQ (8);</source> |
| <p>To start a channel without multicasting, you would want to use the value <code>Channel.SND_RX_SEQ | Channel.SND_TX_SEQ</code> |
| that equals to <code>3</code>. |
| </p> |
| </attribute> |
| |
| <attribute name="heartbeatBackgroundEnabled" required="false"> |
| <p>Flag whether invoke channel heartbeat at container background thread. Default value is false. |
| Enable this flag don't forget to disable the channel heartbeat thread. |
| </p> |
| </attribute> |
| |
| <attribute name="notifyLifecycleListenerOnFailure" required="false"> |
| <p>Flag whether notify LifecycleListeners if all ClusterListener couldn't accept channel message. |
| Default value is false. |
| </p> |
| </attribute> |
| </attributes> |
| </subsection> |
| </section> |
| </body> |
| </document> |