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<!DOCTYPE document [
  <!ENTITY project SYSTEM "project.xml">
]>
<document url="cluster-membership.html">

  &project;

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

<body>

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

<section name="Introduction">
  <p>
    The membership component in the Apache Tribes <a href="cluster-channel.html">Channel</a> is responsible
    for dynamic discovery of other members(nodes) in the cluster.
  </p>
</section>

<section name="Default Implementation">
  <p>
    The default implementation of the cluster group notification is built on top of multicast heartbeats
    sent using UDP packets to a multicast IP address.
    Cluster members are grouped together by using the same multicast address/port combination.
    Each member sends out a heartbeat with a given interval (<code>frequency</code>), and this
    heartbeat is used for dynamic discovery.
    In a similar fashion, if a heartbeat has not been received in a timeframe specified by <code>dropTime</code>
    ms. a member is considered suspect and the channel and any membership listener will be notified.
  </p>
</section>



<section name="Attributes">

  <subsection name="Multicast Attributes">

  <attributes>

    <attribute name="className" required="true">
      <p>
      The default value is <code>org.apache.catalina.tribes.membership.McastService</code>
      and is currently the only implementation.
      This implementation uses multicast heartbeats for member discovery.
      </p>
    </attribute>
    <attribute name="address" required="false">
      <p>
      The multicast address that the membership will broadcast its presence and listen
      for other heartbeats on. The default value is <code>228.0.0.4</code>
      Make sure your network is enabled for multicast traffic.<br/>
      The multicast address, in conjunction with the <code>port</code> is what
      creates a cluster group. To divide up your farm into several different group, or to
      split up QA from production, change the <code>port</code> or the <code>address</code>
      <br/>Previously known as mcastAddr.
      </p>
    </attribute>
    <attribute name="port" required="false">
      <p>
      The multicast port, the default value is <code>45564</code><br/>
      The multicast port, in conjunction with the <code>address</code> is what
      creates a cluster group. To divide up your farm into several different group, or to
      split up QA from production, change the <code>port</code> or the <code>address</code>
      </p>
    </attribute>
    <attribute name="frequency" required="false">
      <p>
      The frequency in milliseconds in which heartbeats are sent out. The default value is <code>500</code> ms.<br/>
      In most cases the default value is sufficient. Changing this value, simply changes the interval in between heartbeats.
      </p>
    </attribute>
    <attribute name="dropTime" required="false">
      <p>
      The membership component will time out members and notify the Channel if a member fails to send a heartbeat within
      a give time. The default value is <code>3000</code> ms. This means, that if a heartbeat is not received from a
      member in that timeframe, the membership component will notify the cluster of this.<br/>
      On a high latency network you may wish to increase this value, to protect against false positives.<br/>
      Apache Tribes also provides a <a href="cluster-interceptor.html#org.apache.catalina.tribes.group.interceptors.TcpFailureDetector_Attributes"><code>TcpFailureDetector</code></a> that will
      verify a timeout using a TCP connection when a heartbeat timeout has occurred. This protects against false positives.
      </p>
    </attribute>
    <attribute name="bind" required="false">
      <p>
      Use this attribute if you wish to bind your multicast traffic to a specific network interface.
      By default, or when this attribute is unset, it tries to bind to <code>0.0.0.0</code> and sometimes on multihomed hosts
      this becomes a problem.
      </p>
    </attribute>
    <attribute name="ttl" required="false">
      <p>
      The time-to-live setting for the multicast heartbeats.
      This setting should be a value between 0 and 255. The default value is VM implementation specific.
      </p>
    </attribute>
    <attribute name="domain" required="false">
      <p>
      Apache Tribes has the ability to logically group members into domains, by using this domain attribute.
      The <code>org.apache.catalina.tribes.Member.getDomain()</code> method returns the value specified here.
      </p>
    </attribute>
    <attribute name="soTimeout" required="false">
      <p>
      The sending and receiving of heartbeats is done on a single thread, hence to avoid blocking this thread forever,
      you can control the <code>SO_TIMEOUT</code> value on this socket.<br/>
      If a value smaller or equal to 0 is presented, the code will default this value to frequency
      </p>
    </attribute>
    <attribute name="recoveryEnabled" required="false">
      <p>
      In case of a network failure, Java multicast socket don't transparently fail over, instead the socket will continuously
      throw IOException upon each receive request. When recoveryEnabled is set to true, this will close the multicast socket
      and open a new socket with the same properties as defined above.<br/>
      The default is <code>true</code>. <br/>
      </p>
    </attribute>
    <attribute name="recoveryCounter" required="false">
      <p>
      When <code>recoveryEnabled==true</code> this value indicates how many
      times an error has to occur before recovery is attempted. The default is
      <code>10</code>. <br/>
      </p>
    </attribute>
    <attribute name="recoverySleepTime" required="false">
      <p>
      When <code>recoveryEnabled==true</code> this value indicates how long time (in milliseconds)
      the system will sleep in between recovery attempts, until it recovers successfully.
      The default is <code>5000</code> (5 seconds). <br/>
      </p>
    </attribute>

    <attribute name="localLoopbackDisabled" required="false">
      <p>
      Membership uses multicast, it will call <code>java.net.MulticastSocket.setLoopbackMode(localLoopbackDisabled)</code>.
      When <code>localLoopbackDisabled==true</code> multicast messages will not reach other nodes on the same local machine.
      The default is <code>false</code>. <br/>
      </p>
    </attribute>

  </attributes>

  </subsection>

</section>

</body>

</document>
