During data migration or code upgrade, I really need a nice way to alert users that I need to bounce server off without interrupting their works. Traditionally, I will send an email to notify all users, and then go to service and shut it down.
There is another trick to drain user from AOS
1. Click System administration > Common > Users > Online users.
2. On the Server instances tab, select the AOS instance that you want to perform maintenance on.
3. Click Reject new clients.
4. When you are prompted, click OK to stop the AOS instance from accepting new client connections.
5. After you have finished performing maintenance on the server, click Accept new clients or restart the AOS instance.