One of my sites runs behind two Varnish dedicated servers with something like 12 web servers running Pressflow 6 and four MySQL full InnoDB database servers. This more than handles the load the site runs on.....until.....I put it into maintenance mode.
At this point Varnish stops caching the pages as they aren't sending HTTP 200.
The load average on the Apache/PHP boxes shoots very quickly to above 100 and in general the boxes are looking for cliffs to jump off.
I'm wondering what others do about this.
I think these are some options.
1 Cache the maintenance mode return code (503) in Varnish
1.1 I'm worried about caching 503s during normal site operation
1.2 I guess I could cache them for something very small like 2 seconds.
2 Select a completely separate backend which is purely static
2.1 I don't really want to have to load new vcl
3 Have Varnish probe the backends and remove them should they return 503 and then serve the vcl_error page to users.
3.1 I'd be fine to do this if the site didn't have regional variations like .co.uk, .fr, .de, .com as we only take one down at a time and they have separate databases.
4 Fix maintenance mode performance?
5.....?
Any opinions on these or shared experiences on how you do it now?
