In JBoss startup process, JBoss starts HTTP/AJP connectors when Server.START_NOTIFICATION_TYPE received, so all applications are available when a time the connectors are started.
This feature has not been implemented for shutdown.
In JBoss shutdown, JBoss undeploys web applications before stopping the connectors. In this case applications are not available in some timeframe during the undeployment, and clients may receive 503 or 404 errors. We can ensure applications availablity in a same manner as startup, by Server.STOP_NOTIFICATION_TYPE.