<?xml version="1.0"?>
<!--
  Licensed to the Apache Software Foundation (ASF) under one or more
  contributor license agreements.  See the NOTICE file distributed with
  this work for additional information regarding copyright ownership.
  The ASF licenses this file to You under the Apache License, Version 2.0
  (the "License"); you may not use this file except in compliance with
  the License.  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
-->
<!DOCTYPE document [
  <!ENTITY project SYSTEM "project.xml">
]>
<document url="cluster-channel.html">

  &project;

  <properties>
    <author email="fhanik@apache.org">Filip Hanik</author>
    <title>The Cluster Channel object</title>
  </properties>

<body>

<section name="Table of Contents">
<toc/>
</section>

<section name="Introduction">
  The cluster channel is the main component of a small framework we've nicknamed Apache Tribes.<br/>
  The channel manages a set of sub components and together they create a group communication framework.<br/>
  This framework is then used internally by the components that need to send messages between different Tomcat instances.
  <br/>
  A few examples of these components would be the SimpleTcpCluster that does the messaging for the DeltaManager,
  or the BackupManager that uses a different replication strategy. The ReplicatedContext object does also
  use the channel object to communicate context attribute changes.
</section>
<section name="Nested Components">
  <p><b><a href="cluster-membership.html">Channel/Membership</a>:</b> <br/>
    The Membership component is responsible for auto discovering new nodes in the cluster
    and also to provide for notifications for any nodes that have not responded with a heartbeat.
    The default implementation uses multicast.<br/>
    In the membership component you configure how your nodes, aka. members, are to be discovered and/or
    divided up.
    You can always find out more about <a href="../tribes/introduction.html">Apache Tribes</a>
  </p>
  <p><b><a href="cluster-sender.html">Channel/Sender</a>:</b> <br/>
    The Sender component manages all outbound connections and data messages that are sent
    over the network from one node to another.
    This component allows messages to be sent in parallel.
    The default implementation uses TCP client sockets, and socket tuning for outgoing messages are
    configured here.<br/>
    You can always find out more about <a href="../tribes/introduction.html">Apache Tribes</a>
  </p>
  <p><b><a href="cluster-sender.html#transport">Channel/Sender/Transport</a>:</b> <br/>
    The Transport component is the bottom IO layer for the sender component.
    The default implementation uses non-blocking TCP client sockets.<br/>
    You can always find out more about <a href="../tribes/introduction.html">Apache Tribes</a>
  </p>
  <p><b><a href="cluster-receiver.html">Channel/Receiver</a>:</b> <br/>
    The receiver component listens for messages from other nodes.
    Here you will configure the cluster thread pool, as it will dispatch incoming
    messages to a thread pool for faster processing.
    The default implementation uses non-blocking TCP server sockets.<br/>
    You can always find out more about <a href="../tribes/introduction.html">Apache Tribes</a>
  </p>
  <p><b><a href="cluster-interceptor.html">Channel/Interceptor</a>:</b> <br/>
    The channel will send messages through an interceptor stack. Because of this, you have the ability to
    customize the way messages are sent and received, and even how membership is handled.<br/>
    You can always find out more about <a href="../tribes/introduction.html">Apache Tribes</a>
  </p>
</section>


<section name="Attributes">

  <subsection name="Common Attributes">

  <attributes>

    <attribute name="className" required="true">
       The default value here is <code>org.apache.catalina.tribes.group.GroupChannel</code> and is
       currently the only implementation available.
    </attribute>


  </attributes>


  </subsection>

  <subsection name="org.apache.catalina.tribes.group.GroupChannel Attributes">

    <attributes>

      <attribute name="heartbeat" required="false">
         Flag whether the channel manages its own heartbeat.
         If set to true,  the channel start a local thread for the heart beat.
         If set this flag to false, you must set SimpleTcpCluster#heartbeatBackgroundEnabled
         to true. default value is true.
      </attribute>

      <attribute name="heartbeatSleeptime" required="false">
        If heartbeat == true, specifies the interval of heartbeat thread in milliseconds.
      </attribute>

      <attribute name="optionCheck" required="false">
        If set to true, the GroupChannel will check the option flags that each
        interceptor is using. Reports an error if two interceptor share the same
        flag.
      </attribute>

    </attributes>

  </subsection>

</section>


</body>

</document>
