7-14 Using Clusters for Oracle WebLogic Server
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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
A migratable server is a clustered Managed Server that has been configured as migratable. These are the key behaviors of a migratable server:
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If you are using a database to manage leasing information, during startup and restart by Node Manager, a migratable server adds a row to the lease table. The
row for a migratable server contains a timestamp, and the machine where it is running.
For more information, see on leasing, see Section 7.3, Leasing.
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When using a database to manage leasing information, a migratable server adds a row to the database as a result of startup, it tries to take on the role of cluster
master, and succeeds if it is the first server instance to join the cluster.
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Periodically, the server renews its lease by updating the timestamp in the lease table.
By default a migratable server renews its lease every 30,000 milliseconds—the product of two configurable ServerMBean properties:
– HealthCheckIntervalMillis, which by default is 10,000.
– HealthCheckPeriodsUntilFencing, which by default is 3.
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If a migratable server fails to reach the lease table and renew its lease before the lease expires, it terminates as quickly as possible using a Java System.exit—in
this case, the lease table still contains a row for that server instance. For information about how this relates to automatic migration, see
Section 7.4.4.7, Cluster Master Role in Whole Server Migration.
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During operation, a migratable server listens for heartbeats from the cluster master. When it detects that the cluster master is not sending heartbeats, it
attempts to take over the role of cluster master, and succeeds if no other server instance has claimed that role.
7.4.4.6 Node Manager Role in Whole Server Migration
The use of Node Manager is required for server migration—it must run on each machine that hosts, or is intended to host.
Node Manager supports server migration in these ways:
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Node Manager must be used for initial startup of migratable servers.
Note: During server migration, keep in mind that server startup
taxes CPU utilization. You cannot assume that because a machine can support x number of servers running concurrently that they also can
support that same number of servers starting up on the same machine at the same time.
Whole Server Migration 7-15
When you initiate the startup of a Managed Server from the Administration Console, the Administration Server uses Node Manager to start up the server
instance. You can also invoke Node Manager to start the server instance using the standalone Node Manager client; however, the Administration Server must be
available so that the Managed Server can obtain its configuration.
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Node Manager must be used to suspend, shutdown, or force shutdown migratable servers.
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Node Manager tries to restart a migratable server whose lease has expired on the machine where it was running at the time of failure.
Node Manager performs the steps in the server migration process by running customizable shell scripts, provided with WebLogic Server, that start, restart and
stop servers; migrate IP addresses; and mount and unmount disks. The scripts are available for Solaris and Linux.
– In an automatic migration, the cluster master invokes Node Manager to
perform the migration.
– In a manual migration, the Administration Server invokes Node Manager to
perform the migration.
7.4.4.7 Cluster Master Role in Whole Server Migration
