All-at-once - non-Java applications only: the update will be applied to all your servers at the same time. Whether sessions are lost or not, depends on your web server.

Full restart - Java only: the update will restart all your application servers at the same time, so there will be downtime for users. Sessions are lost.

Hotpatch - Java only: the update will be applied instantly in the running JVM, without any restart or redeploy. No sessions or state is lost.

Rolling Restarts - The update will be applied to all servers at different times, so there will be no downtime for users. Sessions are drained between servers. If applicable, Java application servers are restarted during the application update.