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1.2.6 Levels of WebSphere system availability

We can deploy WebSphere systems with different redundant hardware, software, networks, processes and components. For the convenience of our discussion, we can roughly divide the deployment into several availability levels. Features discussed for a level are always available for all higher levels also.

Notes - HA levels 1 to 4:

- A DMZ is not shown in the diagrams for WebSphere HA levels 1 to 4. If you want to establish a DMZ, we recommend to move the HTTP server onto a separate system (or LPAR) rather than collocating it with the appserver.

- For simplicity reasons, we did not add an LDAP directory server in the level 1 to 4 diagrams. You can either collocate your LDAP directory on (one of) the system or add a separate system.

- We refer simply to the database for these four HA levels. The database can, however, include application data, session data, ME data stores, and so on. Therefore, a failure in the database can affect different areas of your WAS environment. Refer to the "Possible single points of failure" section of each HA level for the list of data that can become a single point of failure for this configuration.

The transaction logs reside on the file system. When using horizontal clustering (HA levels 3 and higher), this should be a shared file system which supports lease based locking to allow other cluster members to recover in-flight transactions of a failed appserver. For more information, see WebSphere system HA level 3 and 6.7, Transaction Manager high availability.

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