Just like the favicons post of yore, this is another one that came up in conversation, “Can we display a custom maintenance page for each subdomain?” Since I had managed to sketch out a proof-of-concept with the favicons I figured this one shouldn’t be too hard.

The way this works is that Apache checks for a file called maintenance.on and if it exists it rewrites all traffic to maintenance-[subdomain].html. In practice, maintenance.on is set during deploys that require downtime such as one that might do work on the database, and at the end of a successful deploy the file is either removed or moved to something like maintenance.off.

Granted, this is a little kludgy as it depends on a separate html file for each subdomain and I don’t have a fallback position if that maintenance file doesn’t exist, Apache will just serve up a 404.

Anyway, here’s what’s in the Apache site file:

# Check for the maintenance.on file and redirect all requests to
# to a custom maintenance page based on the following formula
# maintenance-[subdomain].html
# get the requested subdomain name into variable %1
RewriteCond %{HTTP_HOST} ^([^.]+)\.*


# skip the rules for images and css
RewriteCond %{REQUEST_URI} !\.(png|jpg|jpeg|gif|css|ico)$


# check to see if maintenance.on exists
RewriteCond %{DOCUMENT_ROOT}/system/maintenance.on -f
RewriteCond %{SCRIPT_FILENAME} !maintenance-1%.html


# write out the custom maintenance page based on the domain
RewriteRule ^.*$ /system/maintenance-%1.html [L]


This was gratefully stolen and extended from the Codahale post, Time For A Grown-Up Server: Rails, Mongrel, Apache, Capistrano and You.