Whenever the server is unavailable (running ghost restart for example), the maintenance.html file takes over and displays the following:
We'll be right back.
We're busy updating our site to give you the best experience, and will be back soon.
Can we create our own maintenance file to override the existing one and if so, should that a file with the same filename be placed in the theme or somewhere else? Does overriding it require anything else?
The maintenance file is used before a majority of Ghost has started up, so it is intentionally not customizable. The only way to override it is by hacking the core, which you’ll have to do every time you update Ghost.
It is mostly proxy server thing. I have created simple maintenance page which is displayed when website’s offline due to proxy settings. Caddy proxy do it well.