Features That Use Leasing Leasing Versions

Whole Server Migration 7-3 ■ Administration Server—used to configure migratable servers and target machines, to obtain the run-time state of migratable servers, and to orchestrate the manual migration process. ■ Floating IP address—an IP address that follows a server from one physical machine to another after migration.

7.3 Leasing

Leasing is the process WebLogic Server uses to manage services that are required to run on only one member of a cluster at a time. Leasing ensures exclusive ownership of a cluster-wide entity. Within a cluster, there is a single owner of a lease. Additionally, leases can failover in case of server or cluster failure. This helps to avoid having a single point of failure.

7.3.1 Features That Use Leasing

The following WebLogic Server features use leasing: ■ Automatic Whole Server Migration—Uses leasing to elect a cluster master. The cluster master is responsible for monitoring other cluster members. It is also responsible for restarting failed members hosted on other physical machines. Leasing ensures that the cluster master is always running, but is only running on one server at a time within a cluster. For information on the cluster master, see Section 7.4.4.7, Cluster Master Role in Whole Server Migration. ■ Automatic Service Migration—JMS-related services, singleton services, and the JTA Transaction Recovery Service can be configured to automatically migrate from an unhealthy hosting server to a healthy active server with the help of the health monitoring subsystem. When the migratable target is migrated, the pinned service hosted by that target is also migrated. Migratable targets use leasing to accomplish automatic service migration. See Chapter 8, Service Migration. ■ Singleton Services—A singleton service is, by definition, a service running within a cluster that is available on only one member of the cluster at a time. Singleton services use leasing to accomplish this. See Section 8.8.1.1, Singleton Master. ■ Job Scheduler—The Job Scheduler is a persistent timer that is used with in a cluster. The Job Scheduler uses the timer master to load balance the timer across a cluster. Although you can use the non-database version, consensus leasing, with the Job Scheduler, this feature requires an external database to maintain failover and replication information.

7.3.2 Leasing Versions

WebLogic Server provides two types of leasing functionality. Which one you use depends on your requirements and your environment. ■ High-availability database leasing—This version of leasing requires a high-availability database to store leasing information. For information on general requirements and configuration, see Section 7.3.4, High-availability Database Leasing. Note: Beyond basic configuration, most leasing functionality is handled internally by WebLogic Server. 7-4 Using Clusters for Oracle WebLogic Server ■ Non-database consensus leasing—This version of leasing stores the leasing information in-memory within a cluster member. This version of leasing requires that all servers in the cluster are started by Node Manager. For more information, see Section 7.3.5, Non-database Consensus Leasing. Within a WebLogic Server installation, you can use only one type of leasing. Although it is possible to implement multiple features that use leasing within your environment, each must use the same kind of leasing. When switching from one leasing type to another, you must restart the entire cluster, not just the Administration Server. Changing the leasing type cannot be done dynamically.

7.3.3 Determining Which Type of Leasing To Use