We have Varnish 3.0.2 running on Amazon's Linux and it works great. We have a ttl of 48 hours for most content pages and much longer for images, PDFs etc.
This weekend we've taken the backend down for some maintenance, so I upped the ttl to 5 days earlier in the week. I had assumed that anything in cache would continue to be served for up to 5 days, but much to our disappointment we checked
varnishstat this morning and the cache was almost completely empty and varnish was serving "page not found" messages.
I know that this is not what Varnish is designed to do, but why would it reset its cache when the backend is down? And how can I prevent it for next time?
Update 2012-06-11: After looking in the /var/log/messages I see every 3 hours or so:
Jun 9 03:56:31 idea-varnish varnishd: Manager got SIGINT Jun 9 03:56:33 idea-varnish varnishd: Platform: Linux,3.2.18-1.26.6.amzn1.x86_64,x86_64,-smalloc,-smalloc,-hcritbit Jun 9 03:56:33 idea-varnish varnishd: child (6709) Started Jun 9 03:56:33 idea-varnish varnishd: Child (6709) said Child starts
I guess this is the server crashing and wiping all the objects in memory. I have only just now installed the -debuginfo rpm but not sure that will actually show anything more.
I supposed we could have switched back to disk-based storage during the scheduled downtime? or would a crash like this wipe that anyway?