Use Varnish to provide a static HTML page whilst your site is in maintenance mode.
A site in maintenance mode may still receive traffic - although those visitors would typically see a simple "Site is under maintenance" message, that traffic is still hitting and running Drupal.
If you use varnish, this traffic can be serviced by the reverse proxy, which means it doesn't need to hit Drupal. This can simplify your maintenance process by eliminating unnecessary traffic, improve the performance of any maintenance updates, and allow updates to be tested in private before releasing a new site to the public.
This module allows administrators to provide static HTML for varnish to display whilst the site is in maintenance mode. The module uses the maintenance mode API module to detect when the site switches into maintenance mode, and instructs varnish (using the admin port) to use a custom VCL which is provided.
If (as an administrator) your only way into the site is via varnish, this will lock you out of your site. This is not recommended! Ensure you have an alternative way to access your site - on a different IP, on a different port, etc...or you could find yourself out in the cold.
- The Maintenance 200 module returns a 200 status code in maintenance mode, which lets Varnish cache responses whilst in maintenance mode.