Consider adding expiration/TTL to maintenance page to help avoid caching maintenance page for too long

[gilbertozp]

The maintenance page (error503.html) doesn't have an expiration timestamp. Adding one, e.g., for 1-2h in the future, might help with preventing browsers/http caches for keeping the page without updates for longer than necessary after returning to normal operations.

Adding and "expires" tag might be one way to go:
<meta http-equiv="expires" content="Tue, 01 Jan 1980 1:00:00 GMT" />

Ref: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Expires

Adding cache control might also be an option (maybe works better with http proxy caches?):
Ref: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control