Using Weblogic Clusters

http://download.oracle.com/docs/cd/E13222_01/wls/docs103/cluster/index.html

Cluster configuration
http://download.oracle.com/docs/cd/E13222_01/wls/docs103/cluster/config.html

Setting up WebLogic Clusters
http://download.oracle.com/docs/cd/E13222_01/wls/docs103/cluster/setup.html

Cluster Architectures
http://download.oracle.com/docs/cd/E13222_01/wls/docs103/cluster/planning.html#wp1028504

 <server>
    <name>AdminServer</name>
    <machine>Machine_1</machine>
    <listen-address></listen-address>
  </server>
  <server>
    <name>ManagedServer_1</name>
    <machine>Machine_1</machine>
    <listen-port>7002</listen-port>
    <cluster>Cluster_1</cluster>
    <listen-address>localhost</listen-address>
    <jta-migratable-target>
      <user-preferred-server>ManagedServer_1</user-preferred-server>
      <cluster>Cluster_1</cluster>
    </jta-migratable-target>
  </server>
  <server>
    <name>ManagedServer_2</name>
    <machine>Machine_1</machine>
    <listen-port>7003</listen-port>
    <cluster>Cluster_1</cluster>
    <listen-address>localhost</listen-address>
    <jta-migratable-target>
      <user-preferred-server>ManagedServer_2</user-preferred-server>
      <cluster>Cluster_1</cluster>
    </jta-migratable-target>
  </server>
  <cluster>
    <name>Cluster_1</name>
    <multicast-address>239.192.0.0</multicast-address>
    <multicast-port>7005</multicast-port>
    <cluster-messaging-mode>multicast</cluster-messaging-mode>
  </cluster>

 <machine>
    <name>Machine_1</name>
    <node-manager>
      <name>Machine_1</name>
      <listen-address>localhost</listen-address>
    </node-manager>
  </machine>
  <migratable-target>
    <name>ManagedServer_1 (migratable)</name>
    <notes>This is a system generated default migratable target for a server. Do not delete manually.</notes>
    <user-preferred-server>ManagedServer_1</user-preferred-server>
    <cluster>Cluster_1</cluster>
  </migratable-target>
  <migratable-target>
    <name>ManagedServer_2 (migratable)</name>
    <notes>This is a system generated default migratable target for a server. Do not delete manually.</notes>
    <user-preferred-server>ManagedServer_2</user-preferred-server>
    <cluster>Cluster_1</cluster>
  </migratable-target>
  <admin-server-name>AdminServer</admin-server-name>