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 Note:

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 Zend Server Cluster Manager cluster, and only add it back to the pool after you have successfully added it to the ZSCM cluster.

To initiate a Graceful Shutdown, follow the following procedure:

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.
Log in to the Zend Server Cluster Manager GUI and Navigate to Cluster Setup | Servers
Select the server you want to remove from the cluster, and click “Remove”
The server’s status should indicate that it is shutting down. This process may take between a few seconds and a minute, depending on the number and size of sessions and on your network throughput.

Refresh the Servers list. If the server is no longer listed, it has been successfully removed.

If you plan to remove more than one server, repeat this process for each server after receiving confirmation that the previous server has been removed. Shutting servers down one by one is required to ensure information consistency. While a server is being removed you will not be able to add, edit or remove any other servers.

When adding a server which has been removed using Graceful Shutdown back to the cluster, make sure to only connect the server to your load balancing pool after the servers list indicate that the server is in “Ok” status.