Zend Server User Guide > Concepts > Graceful Shutdown

Graceful Shutdown

Session Clustering's Graceful Shutdown allows removing a server from a cluster for administrative purposes (such as maintenance) without risking session data loss.

Graceful Shutdown works by transferring all the sessions stored on the server being removed from the cluster to one of the other servers in the cluster. After transferring all the sessions, the server will notify other cluster members that it has been replaced. Requests for sessions originally stored on the now terminated server will be routed to the replacement server.

It is highly recommended to perform graceful shutdowns when using Session Clustering, especially when shutting down more than one server, to avoid potential session data loss.

Important:

When a server is in the process of shutting down or is being started up after a graceful shutdown, it will not allow the session handler to create new sessions until this process is complete. You should always disconnect the server from the load balancing pool before removing it from the cluster, and only add it back to the pool after you have successfully added it to the cluster.

Instructions on how to complete a procedure

To initiate a Graceful Shutdown:

Remove the server you intend to shut down from your load balancing pool. This should be done following the recommended procedure depending on your load balancing configuration.
Perform one of the following operations:

Disable a server - Also available using the Web API.
Remove a server - Also available using the Web API.

Note:

The load will increase on active nodes during this process since some of the node's sessions are moved to other nodes.

	Read Also
	Managing Servers
	Changing Cluster Configurations
	Session Clustering