WebSphere Application Server HAManager Settings

Sometimes customers get conflicting advice on the WebSphere Application Server HAManager component like so ...

1. I would enable HA on everything........ Even if applications aren't using it or don't need it, there are components/functions of WAS that rely on it 
2. You can disable the HA Manager if the applications do not require it 

The two statements are less conflicting than they may appear. The points to consider when enabling or disabling HAManager with WebSphere are as follows:

1. The HA Manager will use a certain amount of resources (CPU and memory).
2. There are a number of WebSphere components (Memory-to-memory cache replication, Session memory persistence, Stateful Session Bean failover, Singleton failover, Workload management routing, On-demand configuration routing & transaction log failover) that use the HA Manager. These components will add their own resource usage on top of what the HA Manager uses by itself. Depending on the topology, that resource usage may be significant.
3. New dependencies can be created on the HA Manager at any time. These dependencies may be added in the service streams (Feature in Service). While we strive to keep the list of dependencies (in the Info Center or Large Topology White Paper) up-to-date, new dependencies can be added without our knowledge.
4. Customers may consider disabling the HA Manager to save resource.

Generally speaking, we don't recommend that customers disable the HA Manager. We do recommend applying the most current tuning. A number of customers have disabled the HA Manager and caused themselves problems. The most common symptom will be an application routing issue. If a customer decides to disable the HA Manager, proceed with caution. Realize that you may need to re-enable it in the future.