Application update involves distributing new application binaries to each of the servers in a cluster during configuration synchronization.
The objective of any high availability configuration is to eliminate all single points of failure (SPOFs).
For manual application rollout, workload routing is controlled by stopping the application server on which the cluster member being updated resides. This results in a quiesce of that server. All existing requests already in the server are allowed to complete, but no new requests are accepted. Both the sysplex distributor and the WebSphere® Application Server Web server plug-in routes work away from the quiescing server. After all work has completed, you start the application update process on this server.
You can set up your system to perform automatic application rollout for your high availability applications. The automatic application rollout update process stops or pauses each application server that is hosting a cluster member that needs updating.
Instead of stopping the application server, you can use the MVS console Modify command to pause the listeners for that application server, perform the application update, and then resume the listeners. If you use this technique, you do not have to stop and then start the server to perform the application update.