When a WEBCON BPS environment goes offline for an update, users opening the portal see a generic IIS error with no context. A dedicated maintenance page tells them what is happening, when the system will return, and who to contact.
The solution consists of a PowerShell script that sets up a second IIS site on a separate port using the same certificate, and a static HTML page with configurable multilingual content. Switching to maintenance mode and back is a matter of swapping port numbers between the two sites.

If you are interested in this, you can find more information in this blog post.