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
In a cluster that contains migratable servers, one server instance acts as the cluster master. Its role is to orchestrate the server migration process. Any server instance in
the cluster can serve as the cluster master. When you start a cluster that contains migratable servers, the first server to join the cluster becomes the cluster master and
starts up the cluster manager service. If a cluster does not include at least one migratable server, it does not require a cluster master, and the cluster manager service
does not start up. In the absence of a cluster master, migratable servers can continue to operate, but server migration is not possible. These are the key functions of the cluster
master:
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Issues periodic heartbeats to the other servers in the cluster.
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Periodically reads the lease table to verify that each migratable server has a current lease. An expired lease indicates to the cluster master that the migratable server
should be restarted.
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Upon determining that a migratable servers lease is expired, waits for period specified by the FencingGracePeriodMillis on the ClusterMBean, and then
tries to invoke the Node Manager process on the machine that hosts the migratable server whose lease is expired, to restart the migratable server.
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If unable to restart a migratable server whose lease has expired on its current machine, the cluster master selects a target machine in this fashion:
– If you have configured a list of preferred destination machines for the
migratable server, the cluster master chooses a machine on that list, in the order the machines are listed.
– Otherwise, the cluster master chooses a machine on the list of those configured
as available for hosting migratable servers in the cluster.
Note: Migration of a server instance that is not initially started with
Node Manager will fail.
7-16 Using Clusters for Oracle WebLogic Server
A list of machines that can host migratable servers can be configured at two levels: for the cluster as a whole, and for an individual migratable server. You
can define a machine list at both levels. You must define a machine list on at least one level.
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To accomplish the migration of a server instance to a new machine, the cluster master invokes the Node Manager process on the target machine to create a
process for the server instance.
The time required to perform the migration depends on the server configuration and startup time.
– The maximum time taken for the cluster master to restart the migratable
server is HealthCheckPeriodsUntilFencing HealthCheckIntervalMillis + FencingGracePeriodMillis.
– The total time before the server becomes available for client requests depends
on the server startup time and the application deployment time.
8
Service Migration 8-1
8
Service Migration
The following sections describe the service migration mechanisms supported by WebLogic Server:
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Section 8.1, Understanding the Service Migration Framework
