7-12 Using Clusters for Oracle WebLogic Server
2.
Upon its next periodic review of the lease table, the cluster master detects that Managed Server 2s lease has expired. See
Section 7.4.4.7, Cluster Master Role in Whole Server Migration.
3.
The cluster master tries to contact Node Manager on Machine C to restart Managed Server 2, but fails, because Machine C is unreachable.
4.
The cluster master contacts Node Manager on Machine D, which is configured as an available host for migratable servers in the cluster.
5.
Node Manager on Machine D starts Managed Server 2. See Section 7.4.4.6, Node
Manager Role in Whole Server Migration.
6.
Managed Server 2 starts up and contacts the Administration Server to obtain its configuration.
7.
Managed Server 2 caches the configuration with which it started up.
8.
Managed Server 2 obtains a migratable server lease. During migration, the clients of the Managed Server that is migrating may experience
a brief interruption in service; it may be necessary to reconnect. On Solaris and Linux operating systems, this can be done using the ifconfig command. The clients of a
migrated server do not need to know the particular machine to which it has migrated.
When a machine that previously hosted a server instance that was migrated becomes available again, the reversal of the migration process—migrating the server instance
back to its original host machine—is known as failback. WebLogic Server does not automate the process of failback. An administrator can accomplish failback by
manually restoring the server instance to its original host.
The general procedures for restoring a server to its original host are as follows:
■
Gracefully shutdown the new instance of the server
■
After you have restarted the failed machine, restart Node Manager and the Managed Server.
The exact procedures you will follow depend on your server and network environment.
7.4.4.3 Manual Whole Server Migration Process
Figure 7–3 illustrates what happens when an administrator manually migrates a
migratable server.
Note: If the Managed Server 2 lease had expired because it was
hung, and Machine C was reachable, the cluster master would use Node Manager to restart Managed Server 2 on Machine C.
Whole Server Migration 7-13
Figure 7–3 Manual Whole Server Migration
1.
An administrator uses the Administration Console to initiate the migration of Managed Server 2 from Machine C to Machine B.
2.
The Administration Server contacts Node Manager on Machine C. See Section 7.4.4.4, Administration Server Role in Whole Server Migration.
3.
Node Manager on Machine C stops Managed Server 2.
4.
Managed Server 2 removes its row from the lease table.
5.
The Administration Server invokes Node Manager on Machine B.
6.
Node Manager on Machine B starts Managed Server 2.
7.
Managed Server 2 obtains its configuration from the Administration Server.
8.
Managed Server 2 caches the configuration with which it started up.
9.
Managed Server 2 adds a row to the lease table.
7.4.4.4 Administration Server Role in Whole Server Migration
In a cluster that contains migratable servers, the Administration Server:
■
Invokes Node Manager, on each machine that hosts cluster members, to start up the migratable servers. This is a prerequisite for server migratability—if a server
instance was not initially started by Node Manager, it cannot be migrated.
■
Invokes Node Manager on each machine involved in a manual migration process to stop and start the migratable server.
7-14 Using Clusters for Oracle WebLogic Server
■
Invokes Node Manager on each machine that hosts cluster members to stop server instances during a normal shutdown. This is a prerequisite for server
migratability—if a server instance is shut down directly, without using Node Manager, when the cluster master detects that the server instance is not running, it
will call Node Manager to restart it.
In addition, the Administration Server provides its regular domain management functionality, persisting configuration updates issued by an administrator, and
providing a run-time view of the domain, including the migratable servers it contains.
7.4.4.5 Migratable Server Behavior in a Cluster
