Adding a cluster to a bus for high availability or scalability
You can add a cluster as a member of a bus and use messaging engine policy assistance and a predefined messaging engine policy that provides high availability, scalability, or scalability with high availability. Messaging engine policy assistance helps you to create and configure the messaging engines in a cluster to provide the required messaging engine behavior.
Before you begin
About this task
- High availability. Use the high availability policy when you want
to ensure that there is always a messaging engine running in that
cluster, so that messages are always transmitted.
The high availability messaging engine policy creates a single messaging engine for the cluster. The messaging engine is configured to fail over to any of the other servers in the cluster. The order in which the servers are used for failover depends on their order in the preferred servers list. The earlier the server in the preferred servers list, the stronger the preference for that server. The messaging engine does not fail back, that is, if a more preferred server becomes available again, the messaging engine does not move back to that server.
- Scalability. Use the scalability policy for a system where you
want to add more servers to a cluster and maintain the performance.
The scalability messaging engine policy creates a single messaging engine for each server in the cluster. Each messaging engine can run only on the server that it is assigned to, and it cannot fail over to another server. If a server fails, the messaging engine that is running on it also fails, and is not available until the server recovers. You can add new servers to the cluster without affecting existing messaging engines in the cluster.
- Scalability with high availability. Use the scalability with high
availability policy for a system where you want to add more servers
to a cluster and maintain the performance, but you also want to ensure
that messaging is always available.
The scalability with high availability messaging engine policy creates a single messaging engine for each server in the cluster. Each messaging engine can fail over to one other specified server in the cluster. Each server can host up to two messaging engines, such that there is an ordered circular relationship between the servers. Each messaging engine can fail back, that is, if a messaging engine fails over to another server, and then the original server becomes available again, the messaging engine automatically moves back to that server.
You can optionally tune the initial and maximum Java™ virtual machine (JVM) heap sizes. Tuning the heap sizes helps to ensure that application servers hosting one or more messaging engines are provided with an appropriate amount of memory for the message throughput you require.
- 6.0.2 (Fix Pack 23 or later)
- 6.1.0 (Fix Pack 13 or later)
If security is enabled, and the bus has mixed-version bus members, the bus members establish trust by using an inter-engine authentication alias. If you add a server cluster as a bus member at WebSphere Application Server Version 6, and it is the first bus member at this level, you must select or create an authentication alias during this task. This action sets the inter-engine authentication alias.
Procedure
Results
- For the high availability messaging engine policy, there is a single messaging engine, named cluster_name.nnn-bus_name, which can fail over to any of the servers in the cluster.
- For the scalability messaging engine policy, there is one messaging engine for each server in the cluster, named cluster_name.nnn-bus_name. Each messaging engine in the cluster is restricted to running on one server.
- For the scalability with high availability messaging engine policy, there is one messaging engine for each application server in the cluster, named cluster_name.nnn-bus_name. Each messaging engine in the cluster can fail over to one other specified server in the cluster, and can fail back to its preferred server if that server becomes available again.