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1<html><head><META http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><title>Apache Tomcat 6.0 - Clustering/Session Replication HOW-TO</title><meta value="Filip Hanik" name="author"><meta value="fhanik@apache.org" name="email"><meta value="Peter Rossbach" name="author"><meta value="pero@apache.org" name="email"></head><body vlink="#525D76" alink="#525D76" link="#525D76" text="#000000" bgcolor="#ffffff"><table cellspacing="0" width="100%" border="0"><!--PAGE HEADER--><tr><td><!--PROJECT LOGO--><a href="http://tomcat.apache.org/"><img border="0" alt="
2      The Apache Tomcat Servlet/JSP Container
3    " align="right" src="./images/tomcat.gif"></a></td><td><font face="arial,helvetica,sanserif"><h1>Apache Tomcat 6.0</h1></font></td><td><!--APACHE LOGO--><a href="http://www.apache.org/"><img border="0" alt="Apache Logo" align="right" src="./images/asf-logo.gif"></a></td></tr></table><table cellspacing="4" width="100%" border="0"><!--HEADER SEPARATOR--><tr><td colspan="2"><hr size="1" noshade></td></tr><tr><!--LEFT SIDE NAVIGATION--><td nowrap="true" valign="top" width="20%"><p><strong>Links</strong></p><ul><li><a href="index.html">Docs Home</a></li><li><a href="http://wiki.apache.org/tomcat/FAQ">FAQ</a></li></ul><p><strong>User Guide</strong></p><ul><li><a href="introduction.html">1) Introduction</a></li><li><a href="setup.html">2) Setup</a></li><li><a href="appdev/index.html">3) First webapp</a></li><li><a href="deployer-howto.html">4) Deployer</a></li><li><a href="manager-howto.html">5) Manager</a></li><li><a href="realm-howto.html">6) Realms and AAA</a></li><li><a href="security-manager-howto.html">7) Security Manager</a></li><li><a href="jndi-resources-howto.html">8) JNDI Resources</a></li><li><a href="jndi-datasource-examples-howto.html">9) JDBC DataSources</a></li><li><a href="class-loader-howto.html">10) Classloading</a></li><li><a href="jasper-howto.html">11) JSPs</a></li><li><a href="ssl-howto.html">12) SSL</a></li><li><a href="ssi-howto.html">13) SSI</a></li><li><a href="cgi-howto.html">14) CGI</a></li><li><a href="proxy-howto.html">15) Proxy Support</a></li><li><a href="mbeans-descriptor-howto.html">16) MBean Descriptor</a></li><li><a href="default-servlet.html">17) Default Servlet</a></li><li><a href="cluster-howto.html">18) Clustering</a></li><li><a href="balancer-howto.html">19) Load Balancer</a></li><li><a href="connectors.html">20) Connectors</a></li><li><a href="monitoring.html">21) Monitoring and Management</a></li><li><a href="logging.html">22) Logging</a></li><li><a href="apr.html">23) APR/Native</a></li><li><a href="virtual-hosting-howto.html">24) Virtual Hosting</a></li><li><a href="aio.html">25) Advanced IO</a></li><li><a href="extras.html">26) Additional Components</a></li><li><a href="maven-jars.html">27) Mavenized</a></li></ul><p><strong>Reference</strong></p><ul><li><a href="RELEASE-NOTES.txt">Release Notes</a></li><li><a href="config/index.html">Configuration</a></li><li><a href="api/index.html">Javadocs</a></li><li><a href="http://tomcat.apache.org/connectors-doc/">JK 1.2 Documentation</a></li></ul><p><strong>Apache Tomcat Development</strong></p><ul><li><a href="building.html">Building</a></li><li><a href="changelog.html">Changelog</a></li><li><a href="http://wiki.apache.org/tomcat/TomcatVersions">Status</a></li><li><a href="developers.html">Developers</a></li><li><a href="architecture/index.html">Architecture</a></li><li><a href="funcspecs/index.html">Functional Specs.</a></li></ul></td><!--RIGHT SIDE MAIN BODY--><td align="left" valign="top" width="80%"><table cellspacing="4" width="100%" border="0"><tr><td valign="top" align="left"><h1>Apache Tomcat 6.0</h1><h2>Clustering/Session Replication HOW-TO</h2></td><td nowrap="true" valign="top" align="right"><small><a href="printer/cluster-howto.html"><img alt="Printer Friendly Version" border="0" src="./images/printer.gif"><br>print-friendly<br>version
4                    </a></small></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Important Note"><strong>Important Note</strong></a></font></td></tr><tr><td><blockquote>
5<p><b>You can also check the <a href="config/cluster.html">configuration reference documentation.</a></b>
6</p>
7</blockquote></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="For the impatient"><strong>For the impatient</strong></a></font></td></tr><tr><td><blockquote>
8  <p>
9    Simply add <div align="left"><table border="0" cellpadding="0" cellspacing="4"><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#ffffff"><pre>&lt;Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster"/&gt;</pre></td><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr></table></div>
10    to your <code>&lt;Engine&gt;</code> or your <code>&lt;Host&gt;</code> element to enable clustering.
11  </p>
12  <p>
13    Using the above configuration will enable all-to-all session replication
14    using the <code>DeltaManager</code> to replicate session deltas. By all-to-all we mean that the session gets replicated to all the other
15    nodes in the cluster. This works great for smaller cluster but we don't recommend it for larger clusters(a lot of tomcat nodes).
16    Also when using the delta manager it will replicate to all nodes, even nodes that don't have the application deployed.<br>
17    To get around this problem, you'll want to use the BackupManager. This manager only replicates the session data to one backup
18    node, and only to nodes that have the application deployed. Downside of the BackupManager: not quite as battle tested as the delta manager.
19    <br>
20    Here are some of the important default values:<br>
21    1. Multicast address is 228.0.0.4<br>
22    2. Multicast port is 45564 (the port and the address together determine cluster membership.<br>
23    3. The IP broadcasted is <code>java.net.InetAddress.getLocalHost().getHostAddress()</code> (make sure you don't broadcast 127.0.0.1, this is a common error)<br>
24    4. The TCP port listening for replication messages is the first available server socket in range <code>4000-4100</code><br>
25    5. Two listeners are configured <code>ClusterSessionListener</code> and <code>JvmRouteSessionIDBinderListener</code><br>
26    6. Two interceptors are configured <code>TcpFailureDetector</code> and <code>MessageDispatch15Interceptor</code><br>
27    The following is the default cluster configuration:<br>
28    <div align="left"><table border="0" cellpadding="0" cellspacing="4"><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#ffffff"><pre>
29        &lt;Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster"
30                 channelSendOptions="8"&gt;
31
32          &lt;Manager className="org.apache.catalina.ha.session.DeltaManager"
33                   expireSessionsOnShutdown="false"
34                   notifyListenersOnReplication="true"/&gt;
35
36          &lt;Channel className="org.apache.catalina.tribes.group.GroupChannel"&gt;
37            &lt;Membership className="org.apache.catalina.tribes.membership.McastService"
38                        address="228.0.0.4"
39                        port="45564"
40                        frequency="500"
41                        dropTime="3000"/&gt;
42            &lt;Receiver className="org.apache.catalina.tribes.transport.nio.NioReceiver"
43                      address="auto"
44                      port="4000"
45                      autoBind="100"
46                      selectorTimeout="5000"
47                      maxThreads="6"/&gt;
48
49            &lt;Sender className="org.apache.catalina.tribes.transport.ReplicationTransmitter"&gt;
50              &lt;Transport className="org.apache.catalina.tribes.transport.nio.PooledParallelSender"/&gt;
51            &lt;/Sender&gt;
52            &lt;Interceptor className="org.apache.catalina.tribes.group.interceptors.TcpFailureDetector"/&gt;
53            &lt;Interceptor className="org.apache.catalina.tribes.group.interceptors.MessageDispatch15Interceptor"/&gt;
54          &lt;/Channel&gt;
55
56          &lt;Valve className="org.apache.catalina.ha.tcp.ReplicationValve"
57                 filter=""/&gt;
58          &lt;Valve className="org.apache.catalina.ha.session.JvmRouteBinderValve"/&gt;
59
60          &lt;Deployer className="org.apache.catalina.ha.deploy.FarmWarDeployer"
61                    tempDir="/tmp/war-temp/"
62                    deployDir="/tmp/war-deploy/"
63                    watchDir="/tmp/war-listen/"
64                    watchEnabled="false"/&gt;
65
66          &lt;ClusterListener className="org.apache.catalina.ha.session.JvmRouteSessionIDBinderListener"/&gt;
67          &lt;ClusterListener className="org.apache.catalina.ha.session.ClusterSessionListener"/&gt;
68        &lt;/Cluster&gt;   
69    </pre></td><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr></table></div>
70  </p>
71  <p>Will cover this section in more detail later in this document.</p>
72</blockquote></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Cluster Basics"><strong>Cluster Basics</strong></a></font></td></tr><tr><td><blockquote>
73
74<p>To run session replication in your Tomcat 6.0 container, the following steps
75should be completed:</p>
76<ul>
77  <li>All your session attributes must implement <code>java.io.Serializable</code></li>
78  <li>Uncomment the <code>Cluster</code> element in server.xml</li>
79  <li>If you have defined custom cluster valves, make sure you have the <code>ReplicationValve</code>  defined as well under the Cluster element in server.xml</li>
80  <li>If your Tomcat instances are running on the same machine, make sure the <code>tcpListenPort</code>
81      attribute is unique for each instance, in most cases Tomcat is smart enough to resolve this on it's own by autodetecting available ports in the range 4000-4100</li>
82  <li>Make sure your <code>web.xml</code> has the <code>&lt;distributable/&gt;</code> element
83      or set at your <code>&lt;Context distributable="true" /&gt;</code></li>
84  <li>If you are using mod_jk, make sure that jvmRoute attribute is set at your Engine <code>&lt;Engine name="Catalina" jvmRoute="node01" &gt;</code>
85      and that the jvmRoute attribute value matches your worker name in workers.properties</li>
86  <li>Make sure that all nodes have the same time and sync with NTP service!</li>
87  <li>Make sure that your loadbalancer is configured for sticky session mode.</li>
88</ul>
89<p>Load balancing can be achieved through many techniques, as seen in the
90<a href="balancer-howto.html">Load Balancing</a> chapter.</p>
91<p>Note: Remember that your session state is tracked by a cookie, so your URL must look the same from the out
92   side otherwise, a new session will be created.</p>
93<p>Note: Clustering support currently requires the JDK version 1.5 or later.</p>
94<p>The Cluster module uses the Tomcat JULI logging framework, so you can configure logging
95   through the regular logging.properties file. To track messages, you can enable logging on the key:<code>org.apache.catalina.tribes.MESSAGES</code></p>
96</blockquote></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Overview"><strong>Overview</strong></a></font></td></tr><tr><td><blockquote>
97
98<p>To enable session replication in Tomcat, three different paths can be followed to achieve the exact same thing:</p>
99<ol>
100  <li>Using session persistence, and saving the session to a shared file system (PersistenceManager + FileStore)</li>
101  <li>Using session persistence, and saving the session to a shared database (PersistenceManager + JDBCStore)</li>
102  <li>Using in-memory-replication, using the SimpleTcpCluster that ships with Tomcat 6 (lib/catalina-tribes.jar + lib/catalina-ha.jar)</li>
103</ol>
104
105<p>In this release of session replication, Tomcat can perform an all-to-all replication of session state using the <code>DeltaManager</code> or
106   perform backup replication to only one node using the <code>BackupManager</code>.
107   The all-to-all replication is an algorithm that is only efficient when the clusters are small. For larger clusters,  to use
108   a primary-secondary session replication where the session will only be stored at one backup server simply setup the BackupManager. <br>
109   Currently you can use the domain worker attribute (mod_jk &gt; 1.2.8) to build cluster partitions
110   with the potential of having a more scaleable cluster solution with the DeltaManager(you'll need to configure the domain interceptor for this).
111   In order to keep the network traffic down in an all-to-all environment, you can split your cluster
112   into smaller groups. This can be easily achieved by using different multicast addresses for the different groups.
113   A very simple setup would look like this:
114   </p>
115
116<div align="left"><table border="0" cellpadding="0" cellspacing="4"><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#ffffff"><pre>
117        DNS Round Robin
118               |
119         Load Balancer
120          /           \
121      Cluster1      Cluster2
122      /     \        /     \
123  Tomcat1 Tomcat2  Tomcat3 Tomcat4
124</pre></td><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr></table></div>
125
126<p>What is important to mention here, is that session replication is only the beginning of clustering.
127   Another popular concept used to implement clusters is farming, ie, you deploy your apps only to one
128   server, and the cluster will distribute the deployments across the entire cluster.
129   This is all capabilities that can go into with the FarmWarDeployer (s. cluster example at <code>server.xml</code>)</p>
130<p>In the next section will go deeper into how session replication works and how to configure it.</p>
131
132</blockquote></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Cluster Information"><strong>Cluster Information</strong></a></font></td></tr><tr><td><blockquote>
133<p>Membership is established using multicast heartbeats.
134   Hence, if you wish to subdivide your clusters, you can do this by
135   changing the multicast IP address or port in the <code>&lt;Membership&gt;</code> element.
136</p>
137<p>
138   The heartbeat contains the IP address of the Tomcat node and the TCP port that
139   Tomcat listens to for replication traffic. All data communication happens over TCP.
140</p>
141<p>
142    The <code>ReplicationValve</code> is used to find out when the request has been completed and initiate the
143    replication, if any. Data is only replicated if the session has changed (by calling setAttribute or removeAttribute
144    on the session).
145</p>
146<p>
147    One of the most important performance considerations is the synchronous versus asynchronous replication.
148    In a synchronous replication mode the request doesn't return until the replicated session has been
149    sent over the wire and reinstantiated on all the other cluster nodes.
150    Synchronous vs asynchronous is configured using the <code>channelSendOptions</code>
151    flag and is an integer value. The default value for the <code>SimpleTcpCluster/DeltaManager</code> combo is
152    8, which is asynchronous. You can read more on the <a href="tribes/introduction.html">send flag(overview)</a> or the
153    <a href="http://tomcat.apache.org/tomcat-6.0-doc/api/org/apache/catalina/tribes/Channel.html">send flag(javadoc)</a>.
154    During async replication, the request is returned before the data has been replicated. async replication yields shorter
155    request times, and synchronous replication guarantees the session to be replicated before the request returns.
156</p>
157</blockquote></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Bind session after crash to failover node"><strong>Bind session after crash to failover node</strong></a></font></td></tr><tr><td><blockquote>
158<p>
159    If you are using mod_jk and not using sticky sessions or for some reasons sticky session don't
160    work, or you are simply failing over, the session id will need to be modified as it previously contained
161    the worker id of the previous tomcat (as defined by jvmRoute in the Engine element).
162    To solve this, we will use the JvmRouteBinderValve.
163</p>
164<p> 
165    The JvmRouteBinderValve rewrites the session id to ensure that the next request will remain sticky
166    (and not fall back to go to random nodes since the worker is no longer available) after a fail over.
167    The valve rewrites the JSESSIONID value in the cookie with the same name.
168    Not having this valve in place, will make it harder to ensure stickyness in case of a failure for the mod_jk module.
169</p>
170<p>
171    By default, if no valves are configured, the JvmRouteBinderValve is added on.
172    The cluster message listener called JvmRouteSessionIDBinderListener is also defined by default and is used to actually rewrite the
173    session id on the other nodes in the cluster once a fail over has occurred.
174    Remember, if you are adding your own valves or cluster listeners in server.xml then the defaults are no longer valid,
175    make sure that you add in all the appropriate valves and listeners as defined by the default.
176</p>
177<p>
178    <b>Hint:</b><br>
179    With attribute <i>sessionIdAttribute</i> you can change the request attribute name that included the old session id.
180    Default attribuite name is <i>org.apache.catalina.cluster.session.JvmRouteOrignalSessionID</i>.
181</p>
182<p>
183    <b>Trick:</b><br>
184    You can enable this mod_jk turnover mode via JMX before you drop a node to all backup nodes!
185    Set enable true on all JvmRouteBinderValve backups, disable worker at mod_jk
186    and then drop node and restart it! Then enable mod_jk Worker and disable JvmRouteBinderValves again.
187    This use case means that only requested session are migrated.
188</p>
189
190
191
192</blockquote></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Configuration Example"><strong>Configuration Example</strong></a></font></td></tr><tr><td><blockquote>
193    <div align="left"><table border="0" cellpadding="0" cellspacing="4"><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#ffffff"><pre>
194        &lt;Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster"
195                 channelSendOptions="6"&gt;
196
197          &lt;Manager className="org.apache.catalina.ha.session.BackupManager"
198                   expireSessionsOnShutdown="false"
199                   notifyListenersOnReplication="true"
200                   mapSendOptions="6"/&gt;
201          &lt;!--
202          &lt;Manager className="org.apache.catalina.ha.session.DeltaManager"
203                   expireSessionsOnShutdown="false"
204                   notifyListenersOnReplication="true"/&gt;
205          --&gt;       
206          &lt;Channel className="org.apache.catalina.tribes.group.GroupChannel"&gt;
207            &lt;Membership className="org.apache.catalina.tribes.membership.McastService"
208                        address="228.0.0.4"
209                        port="45564"
210                        frequency="500"
211                        dropTime="3000"/&gt;
212            &lt;Receiver className="org.apache.catalina.tribes.transport.nio.NioReceiver"
213                      address="auto"
214                      port="5000"
215                      selectorTimeout="100"
216                      maxThreads="6"/&gt;
217
218            &lt;Sender className="org.apache.catalina.tribes.transport.ReplicationTransmitter"&gt;
219              &lt;Transport className="org.apache.catalina.tribes.transport.nio.PooledParallelSender"/&gt;
220            &lt;/Sender&gt;
221            &lt;Interceptor className="org.apache.catalina.tribes.group.interceptors.TcpFailureDetector"/&gt;
222            &lt;Interceptor className="org.apache.catalina.tribes.group.interceptors.MessageDispatch15Interceptor"/&gt;
223            &lt;Interceptor className="org.apache.catalina.tribes.group.interceptors.ThroughputInterceptor"/&gt;
224          &lt;/Channel&gt;
225
226          &lt;Valve className="org.apache.catalina.ha.tcp.ReplicationValve"
227                 filter=".*\.gif;.*\.js;.*\.jpg;.*\.png;.*\.htm;.*\.html;.*\.css;.*\.txt;"/&gt;
228
229          &lt;Deployer className="org.apache.catalina.ha.deploy.FarmWarDeployer"
230                    tempDir="/tmp/war-temp/"
231                    deployDir="/tmp/war-deploy/"
232                    watchDir="/tmp/war-listen/"
233                    watchEnabled="false"/&gt;
234
235          &lt;ClusterListener className="org.apache.catalina.ha.session.ClusterSessionListener"/&gt;
236        &lt;/Cluster&gt;
237    </pre></td><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr></table></div>
238    <p>
239      Break it down!!
240    </p>
241    <div align="left"><table border="0" cellpadding="0" cellspacing="4"><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#ffffff"><pre>
242        &lt;Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster"
243                 channelSendOptions="6"&gt;
244    </pre></td><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr></table></div>
245    <p>
246      The main element, inside this element all cluster details can be configured.
247      The <code>channelSendOptions</code> is the flag that is attached to each message sent by the
248      SimpleTcpCluster class or any objects that are invoking the SimpleTcpCluster.send method.
249      The description of the send flags is available at <a href="http://tomcat.apache.org/tomcat-6.0-doc/api/org/apache/catalina/tribes/Channel.html">
250      our javadoc site</a>
251      The <code>DeltaManager</code> sends information using the SimpleTcpCluster.send method, while the backup manager
252      sends it itself directly through the channel.
253      <br>For more info, Please visit the <a href="config/cluster.html">reference documentation</a>
254    </p>
255    <div align="left"><table border="0" cellpadding="0" cellspacing="4"><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#ffffff"><pre>
256          &lt;Manager className="org.apache.catalina.ha.session.BackupManager"
257                   expireSessionsOnShutdown="false"
258                   notifyListenersOnReplication="true"
259                   mapSendOptions="6"/&gt;
260          &lt;!--
261          &lt;Manager className="org.apache.catalina.ha.session.DeltaManager"
262                   expireSessionsOnShutdown="false"
263                   notifyListenersOnReplication="true"/&gt;
264          --&gt;       
265    </pre></td><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr></table></div>
266    <p>
267        This is a template for the manager configuration that will be used if no manager is defined in the &lt;Context&gt;
268        element. In Tomcat 5.x each webapp marked distributable had to use the same manager, this is no longer the case
269        since Tomcat 6 you can define a manager class for each webapp, so that you can mix managers in your cluster.
270        Obviously the managers on one node's application has to correspond with the same manager on the same application on the other node.
271        If no manager has been specified for the webapp, and the webapp is marked &lt;distributable/&gt; Tomcat will take this manager configuration
272        and create a manager instance cloning this configuration.
273        <br>For more info, Please visit the <a href="config/cluster-manager.html">reference documentation</a>
274    </p>
275    <div align="left"><table border="0" cellpadding="0" cellspacing="4"><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#ffffff"><pre>
276          &lt;Channel className="org.apache.catalina.tribes.group.GroupChannel"&gt;
277    </pre></td><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr></table></div>
278    <p>
279        The channel element is <a href="tribes/introduction.html">Tribes</a>, the group communication framework
280        used inside Tomcat. This element encapsulates everything that has to do with communication and membership logic.
281        <br>For more info, Please visit the <a href="config/cluster-channel.html">reference documentation</a>
282    </p>
283    <div align="left"><table border="0" cellpadding="0" cellspacing="4"><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#ffffff"><pre>
284            &lt;Membership className="org.apache.catalina.tribes.membership.McastService"
285                        address="228.0.0.4"
286                        port="45564"
287                        frequency="500"
288                        dropTime="3000"/&gt;
289    </pre></td><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr></table></div>
290    <p>
291        Membership is done using multicasting. Please note that Tribes also supports static memberships using the
292        <code>StaticMembershipInterceptor</code> if you want to extend your membership to points beyond multicasting.
293        The address attribute is the multicast address used and the port is the multicast port. These two together
294        create the cluster separation. If you want a QA cluster and a production cluster, the easiest config is to
295        have the QA cluster be on a separate multicast address/port combination the the production cluster.<br>
296        The membership component broadcasts TCP adress/port of itselt to the other nodes so that communication between
297        nodes can be done over TCP. Please note that the address being broadcasted is the one of the
298        <code>Receiver.address</code> attribute.
299        <br>For more info, Please visit the <a href="config/cluster-membership.html">reference documentation</a>
300    </p>
301    <div align="left"><table border="0" cellpadding="0" cellspacing="4"><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#ffffff"><pre>
302            &lt;Receiver className="org.apache.catalina.tribes.transport.nio.NioReceiver"
303                      address="auto"
304                      port="5000"
305                      selectorTimeout="100"
306                      maxThreads="6"/&gt;
307    </pre></td><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr></table></div>
308    <p>
309        In tribes the logic of sending and receiving data has been broken into two functional components. The Receiver, as the name suggests
310        is responsible for receiving messages. Since the Tribes stack is thread less, (a popular improvement now adopted by other frameworks as well),
311        there is a thread pool in this component that has a maxThreads and minThreads setting.<br>
312        The address attribute is the host address that will be broadcasted by the membership component to the other nodes.
313        <br>For more info, Please visit the <a href="config/cluster-receiver.html">reference documentation</a>
314    </p>
315    <div align="left"><table border="0" cellpadding="0" cellspacing="4"><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#ffffff"><pre>
316
317            &lt;Sender className="org.apache.catalina.tribes.transport.ReplicationTransmitter"&gt;
318              &lt;Transport className="org.apache.catalina.tribes.transport.nio.PooledParallelSender"/&gt;
319            &lt;/Sender&gt;
320    </pre></td><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr></table></div>
321    <p>
322        The sender component, as the name indicates is responsible for sending messages to other nodes.
323        The sender has a shell component, the <code>ReplicationTransmitter</code> but the real stuff done is done in the
324        sub component, <code>Transport</code>.
325        Tribes support having a pool of senders, so that messages can be sent in parallel and if using the NIO sender,
326        you can send messages concurrently as well.<br>
327        Concurrently means one message to multiple senders at the same time and Parallel means multiple messages to multiple senders
328        at the same time.
329        <br>For more info, Please visit the <a href="config/cluster-sender.html">reference documentation</a>
330    </p>
331    <div align="left"><table border="0" cellpadding="0" cellspacing="4"><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#ffffff"><pre>
332            &lt;Interceptor className="org.apache.catalina.tribes.group.interceptors.TcpFailureDetector"/&gt;
333            &lt;Interceptor className="org.apache.catalina.tribes.group.interceptors.MessageDispatch15Interceptor"/&gt;
334            &lt;Interceptor className="org.apache.catalina.tribes.group.interceptors.ThroughputInterceptor"/&gt;
335          &lt;/Channel&gt;
336    </pre></td><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr></table></div>
337    <p>
338        Tribes uses a stack to send messages through. Each element in the stack is called an interceptor, and works much like the valves do
339        in the Tomcat servlet container.
340        Using interceptors, logic can be broken into more managable pieces of code. The interceptors configured above are:<br>
341        TcpFailureDetector - verifies crashed members through TCP, if multicast packets get dropped, this interceptor protects against false positives,
342        ie the node marked as crashed even though it still is alive and running.<br>
343        MessageDispatch15Interceptor - dispatches messages to a thread (thread pool) to send message asynchrously.<br>
344        ThroughputInterceptor - prints out simple stats on message traffic.<br>
345        Please note that the order of interceptors is important. the way they are defined in server.xml is the way they are represented in the
346        channel stack. Think of it as a linked list, with the head being the first most interceptor and the tail the last.
347        <br>For more info, Please visit the <a href="config/cluster-interceptor.html">reference documentation</a>
348    </p>
349    <div align="left"><table border="0" cellpadding="0" cellspacing="4"><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#ffffff"><pre>
350          &lt;Valve className="org.apache.catalina.ha.tcp.ReplicationValve"
351                 filter=".*\.gif;.*\.js;.*\.jpg;.*\.png;.*\.htm;.*\.html;.*\.css;.*\.txt;"/&gt;
352    </pre></td><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr></table></div>
353    <p>
354        The cluster uses valves to track requests to web applications, we've mentioned the ReplicationValve and the JvmRouteBinderValve above.
355        The &lt;Cluster&gt; element itself is not part of the pipeline in Tomcat, instead the cluster adds the valve to its parent container.
356        If the &lt;Cluster&gt; elements is configured in the &lt;Engine&gt; element, the valves get added to the engine and so on.
357        <br>For more info, Please visit the <a href="config/cluster-valve.html">reference documentation</a>
358    </p>
359    <div align="left"><table border="0" cellpadding="0" cellspacing="4"><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#ffffff"><pre>
360          &lt;Deployer className="org.apache.catalina.ha.deploy.FarmWarDeployer"
361                    tempDir="/tmp/war-temp/"
362                    deployDir="/tmp/war-deploy/"
363                    watchDir="/tmp/war-listen/"
364                    watchEnabled="false"/&gt;
365    </pre></td><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr></table></div>
366    <p>
367        The default tomcat cluster supports farmed deployment, ie, the cluster can deploy and undeploy applications on the other nodes.
368        The state of this component is currently in flux but will be addressed soon. There was a change in the deployment algorithm
369        between Tomcat 5.0 and 5.5 and at that point, the logic of this component changed to where the deploy dir has to match the
370        webapps directory.
371        <br>For more info, Please visit the <a href="config/cluster-deployer.html">reference documentation</a>
372    </p>
373    <div align="left"><table border="0" cellpadding="0" cellspacing="4"><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#ffffff"><pre>
374          &lt;ClusterListener className="org.apache.catalina.ha.session.ClusterSessionListener"/&gt;
375        &lt;/Cluster&gt;
376    </pre></td><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr></table></div>
377    <p>
378        Since the SimpleTcpCluster itself is a sender and receiver of the Channel object, components can register themselves as listeners to
379        the SimpleTcpCluster. The listener above <code>ClusterSessionListener</code> listens for DeltaManager replication messages
380        and applies the deltas to the manager that in turn applies it to the session.
381        <br>For more info, Please visit the <a href="config/cluster-listener.html">reference documentation</a>
382    </p>
383   
384</blockquote></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Cluster Architecture"><strong>Cluster Architecture</strong></a></font></td></tr><tr><td><blockquote>
385
386<p><b>Component Levels:</b>
387<div align="left"><table border="0" cellpadding="0" cellspacing="4"><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#ffffff"><pre>
388         Server
389           |
390         Service
391           |
392         Engine
393           |  \
394           |  --- Cluster --*
395           |
396         Host
397           |
398         ------
399        /      \
400     Cluster    Context(1-N)                 
401        |             \
402        |             -- Manager
403        |                   \
404        |                   -- DeltaManager
405        |                   -- BackupManager
406        |
407     ---------------------------
408        |                       \
409      Channel                    \
410    ----------------------------- \
411        |                          \
412     Interceptor_1 ..               \
413        |                            \
414     Interceptor_N                    \
415    -----------------------------      \
416     |          |         |             \
417   Receiver    Sender   Membership       \
418                                         -- Valve
419                                         |      \
420                                         |       -- ReplicationValve
421                                         |       -- JvmRouteBinderValve
422                                         |
423                                         -- LifecycleListener
424                                         |
425                                         -- ClusterListener
426                                         |      \
427                                         |       -- ClusterSessionListener
428                                         |       -- JvmRouteSessionIDBinderListener
429                                         |
430                                         -- Deployer
431                                                \
432                                                 -- FarmWarDeployer
433     
434     
435</pre></td><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr></table></div>
436</p>
437
438</blockquote></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="How it Works"><strong>How it Works</strong></a></font></td></tr><tr><td><blockquote>
439<p>To make it easy to understand how clustering works, We are gonna take you through a series of scenarios.
440   In the scenario we only plan to use two tomcat instances <code>TomcatA</code> and <code>TomcatB</code>.
441   We will cover the following sequence of events:</p>
442
443<ol>
444<li><code>TomcatA</code> starts up</li>
445<li><code>TomcatB</code> starts up (Wait that TomcatA start is complete)</li>
446<li><code>TomcatA</code> receives a request, a session <code>S1</code> is created.</li>
447<li><code>TomcatA</code> crashes</li>
448<li><code>TomcatB</code> receives a request for session <code>S1</code></li>
449<li><code>TomcatA</code> starts up</li>
450<li><code>TomcatA</code> receives a request, invalidate is called on the session (<code>S1</code>)</li>
451<li><code>TomcatB</code> receives a request, for a new session (<code>S2</code>)</li>
452<li><code>TomcatA</code> The session <code>S2</code> expires due to inactivity.</li>
453</ol>
454
455<p>Ok, now that we have a good sequence, we will take you through exactly what happens in the session repliction code</p>
456
457<ol>
458<li><b><code>TomcatA</code> starts up</b>
459    <p>
460        Tomcat starts up using the standard start up sequence. When the Host object is created, a cluster object is associated with it.
461        When the contexts are parsed, if the distributable element is in place in web.xml
462        Tomcat asks the Cluster class (in this case <code>SimpleTcpCluster</code>) to create a manager
463        for the replicated context. So with clustering enabled, distributable set in web.xml
464        Tomcat will create a <code>DeltaManager</code> for that context instead of a <code>StandardManager</code>.
465        The cluster class will start up a membership service (multicast) and a replication service (tcp unicast).
466        More on the architecture further down in this document.
467    </p><p></p>
468</li>
469<li><b><code>TomcatB</code> starts up</b>
470    <p>
471        When TomcatB starts up, it follows the same sequence as TomcatA did with one exception.
472        The cluster is started and will establish a membership (TomcatA,TomcatB).
473        TomcatB will now request the session state from a server that already exists in the cluster,
474        in this case TomcatA. TomcatA responds to the request, and before TomcatB starts listening
475        for HTTP requests, the state has been transferred from TomcatA to TomcatB.
476        In case TomcatA doesn't respond, TomcatB will time out after 60 seconds, and issue a log
477        entry. The session state gets transferred for each web application that has distributable in
478        its web.xml. Note: To use session replication efficiently, all your tomcat instances should be
479        configured the same.
480    </p><p></p>
481</li>
482<li><B><code>TomcatA</code> receives a request, a session <code>S1</code> is created.</B>
483    <p>
484        The request coming in to TomcatA is treated exactly the same way as without session replication.
485        The action happens when the request is completed, the <code>ReplicationValve</code> will intercept
486        the request before the response is returned to the user.
487        At this point it finds that the session has been modified, and it uses TCP to replicata the
488        session to TomcatB. Once the serialized data has been handed off to the operating systems TCP logic,
489        the request returns to the user, back through the valve pipeline.
490        For each request the entire session is replicated, this allows code that modifies attributes
491        in the session without calling setAttribute or removeAttribute to be replicated.
492        a useDirtyFlag configuration parameter can be used to optimize the number of times
493        a session is replicated.
494    </p><p></p>
495
496</li>
497<li><b><code>TomcatA</code> crashes</b>
498    <p>
499        When TomcatA crashes, TomcatB receives a notification that TomcatA has dropped out
500        of the cluster. TomcatB removes TomcatA from its membership list, and TomcatA will no longer
501        be notified of any changes that occurs in TomcatB.
502        The load balancer will redirect the requests from TomcatA to TomcatB and all the sessions
503        are current.
504    </p><p></p>
505</li>
506<li><b><code>TomcatB</code> receives a request for session <code>S1</code></b>
507    <p>Nothing exciting, TomcatB will process the request as any other request.
508    </p><p></p>
509</li>
510<li><b><code>TomcatA</code> starts up</b>
511    <p>Upon start up, before TomcatA starts taking new request and making itself
512    available to it will follow the start up sequence described above 1) 2).
513    It will join the cluster, contact TomcatB for the current state of all the sessions.
514    And once it receives the session state, it finishes loading and opens its HTTP/mod_jk ports.
515    So no requests will make it to TomcatA until it has received the session state from TomcatB.
516    </p><p></p>
517</li>
518<li><b><code>TomcatA</code> receives a request, invalidate is called on the session (<code>S1</code>)</b>
519    <p>The invalidate is call is intercepted, and the session is queued with invalidated sessions.
520        When the request is complete, instead of sending out the session that has changed, it sends out
521        an "expire" message to TomcatB and TomcatB will invalidate the session as well.
522    </p><p></p>
523
524</li>
525<li><b><code>TomcatB</code> receives a request, for a new session (<code>S2</code>)</b>
526    <p>Same scenario as in step 3)
527    </p><p></p>
528
529
530</li>
531<li><code>TomcatA</code> The session <code>S2</code> expires due to inactivity.
532    <p>The invalidate is call is intercepted the same was as when a session is invalidated by the user,
533       and the session is queued with invalidated sessions.
534       At this point, the invalidet session will not be replicated across until
535       another request comes through the system and checks the invalid queue.
536    </p><p></p>
537</li>
538</ol>
539
540<p>Phuuuhh! :)</p>
541
542<p><b>Membership</b>
543    Clustering membership is established using very simple multicast pings.
544    Each Tomcat instance will periodically send out a multicast ping,
545    in the ping message the instance will broad cast its IP and TCP listen port
546    for replication.
547    If an instance has not received such a ping within a given timeframe, the
548    member is considered dead. Very simple, and very effective!
549    Of course, you need to enable multicasting on your system.
550</p>
551
552<p><b>TCP Replication</b>
553    Once a multicast ping has been received, the member is added to the cluster
554    Upon the next replication request, the sending instance will use the host and
555    port info and establish a TCP socket. Using this socket it sends over the serialized data.
556    The reason I choose TCP sockets is because it has built in flow control and guaranteed delivery.
557    So I know, when I send some data, it will make it there :)
558</p>
559
560<p><b>Distributed locking and pages using frames</b>
561    Tomcat does not keep session instances in sync across the cluster.
562    The implementation of such logic would be to much overhead and cause all
563    kinds of problems. If your client accesses the same session
564    simultanously using multiple requests, then the last request
565    will override the other sessions in the cluster.
566</p>
567
568</blockquote></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Monitoring your Cluster with JMX"><strong>Monitoring your Cluster with JMX</strong></a></font></td></tr><tr><td><blockquote>
569<p>Monitoring is a very important question when you use a cluster. Some of the cluster objects are JMX MBeans </p>
570<p>Add the following parameter to your startup script with Java 5:
571<div align="left"><table border="0" cellpadding="0" cellspacing="4"><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#ffffff"><pre>
572set CATALINA_OPTS=\
573-Dcom.sun.management.jmxremote \
574-Dcom.sun.management.jmxremote.port=%my.jmx.port% \
575-Dcom.sun.management.jmxremote.ssl=false \
576-Dcom.sun.management.jmxremote.authenticate=false
577</pre></td><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr></table></div>
578</p>
579<p>Activate JMX with JDK 1.4:
580<ol>
581<li>Install the compat package</li>
582<li>Install the mx4j-tools.jar at common/lib (use the same mx4j version as your tomcat release)</li>
583<li>Configure a MX4J JMX HTTP Adaptor at your AJP Connector<p></p>
584<div align="left"><table border="0" cellpadding="0" cellspacing="4"><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#ffffff"><pre>
585&lt;Connector port="${AJP.PORT}"
586   handler.list="mx"
587   mx.enabled="true"
588   mx.httpHost="${JMX.HOST}"
589   mx.httpPort="${JMX.PORT}"
590   protocol="AJP/1.3" /&gt;
591</pre></td><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="./images/void.gif"></td></tr></table></div>
592</li>
593<li>Start your tomcat and look with your browser to http://${JMX.HOST}:${JMX.PORT}</li>
594<li>With the connector parameter <code>mx.authMode="basic" mx.authUser="tomcat" mx.authPassword="strange"</code> you can control the access!</li>
595</ol>
596</p>
597<p>
598List of Cluster Mbeans<br>
599<table border="1" cellpadding="5">
600
601  <tr>
602    <th align="center" bgcolor="aqua">Name</th>
603    <th align="center" bgcolor="aqua">Description</th>
604    <th align="center" bgcolor="aqua">MBean ObjectName - Engine</th>
605    <th align="center" bgcolor="aqua">MBean ObjectName - Host</th>
606  </tr>
607
608  <tr>
609    <td>Cluster</td>
610    <td>The complete cluster element</td>
611    <td><code>type=Cluster</code></td>
612    <td><code>type=Cluster,host=${HOST}</code></td>
613  </tr>
614 
615  <tr>
616    <td>DeltaManager</td>
617    <td>This manager control the sessions and handle session replication </td>
618    <td><code>type=Manager,path=${APP.CONTEXT.PATH}, host=${HOST}</code></td>
619    <td><code>type=Manager,path=${APP.CONTEXT.PATH}, host=${HOST}</code></td>
620  </tr>
621
622  <tr>
623    <td>ReplicationValve</td>
624    <td>This valve control the replication to the backup nodes</td>
625    <td><code>type=Valve,name=ReplicationValve</code></td>
626    <td><code>type=Valve,name=ReplicationValve,host=${HOST}</code></td>
627  </tr>
628
629  <tr>
630    <td>JvmRouteBinderValve</td>
631    <td>This is a cluster fallback valve to change the Session ID to the current tomcat jvmroute.</td>
632    <td><code>type=Valve,name=JvmRouteBinderValve,
633              path=${APP.CONTEXT.PATH}</code></td>
634    <td><code>type=Valve,name=JvmRouteBinderValve,host=${HOST},
635              path=${APP.CONTEXT.PATH}</code></td>
636  </tr>
637
638</table>
639</p>
640</blockquote></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="FAQ"><strong>FAQ</strong></a></font></td></tr><tr><td><blockquote>
641<p>Please see <a href="http://tomcat.apache.org/faq/cluster.html">the clustering section of the FAQ</a>.</p>
642</blockquote></td></tr></table></td></tr><!--FOOTER SEPARATOR--><tr><td colspan="2"><hr size="1" noshade></td></tr><!--PAGE FOOTER--><tr><td colspan="2"><div align="center"><font size="-1" color="#525D76"><em>
643        Copyright &copy; 1999-2008, Apache Software Foundation
644        </em></font></div></td></tr></table></body></html>
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