Thankfully @pixelfed supports custom 503 page title and body (with HTML) so I can add the following .env variables to pixelfed.social to keep users in the loop!

PAGE_503_HEADER="Service Unavailable"
PAGE_503_BODY="We are performing some maintenance to upgrade our database server!<br /><hr/>For updates, follow our <a href='https://status.pixelfed.social/maintenance/234192' target='_blank'>status page incident</a>."