Chapter 17: Clustering . Membership service based on multicast heartbeat and TCP failure detection; dynamically determines the members in a group. . Reliable messaging service between the different members of a group, providing a range of message delivery guarantees. You can configure the exact characteristic of the channel used via: . Configuration of the subelement . Configuration of the and (and associated ) subelements . Configuration of subelements Thorough coverage of the Apache Tribes communications framework is beyond the scope of this chapter; interested readers should peruse the detailed Apache Tribes documentation included with the Tomcat 6 distribution (as part of the webapps/docsapplication). The following subsections explain the specific configuration used in this example. The element has only one attribute as illustrated in the table that follows. Attribute Name Description Default className It must be org.apache.catalina.tribes.group.GroupChannel, the only supported implementation. Configuring the Subelement The subelement configures the membership service. This service is based on sending a multicast heartbeat regularly, and you need to select the frequency, dropTime, and multicast address and port to be used. This service determines and maintains information on the machines that are considered part of the group (cluster) at any point in time. The following table lists some of the attributes on the element. Attribute Name Description Default className address port Currently, only org.apache.catalina.tribes.membership .McastServiceis available. The multicast address selected for this instance. You can use a different multicast address and port to partition your LAN into multiple groups (clusters). However, because of the network traffic that even one replicating cluster generates, this partitioning feature is not as useful as it seems. The multicast port used. You can use a different address:port for multicast to partition your LAN into multiple groups. 228.0.0.4 45564 Table continued on following page
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