Sun GlassFish Enterprise Server v2.1.1 Application Deployment Guide

Dynamic Deployment

You can deploy, redeploy, and undeploy an application or module without restarting the server instances. This is called dynamic deployment. Although primarily for developers, dynamic deployment can be used in operational environments to bring new applications and modules online without requiring a server restart.

Whenever a redeployment is done, the sessions at that transit time become invalid. The client must restart the session.