Sorry if this isn't the right place for this (point me to the right one and I'll go there), but I've encountered an issue with Varnish I can't seem to find help on the web for.
Starting today, at a random time (not sure what triggered it), every single page in the Drupal site started returning a 503 error, service unavailable (no additional information).
I can paste my varnishlog output if that'll help. It's reporting a 503 error in the log output. I've added the 600s timeout recommendations as posted in other threads, and added a snippet to default.vcl which passes on caching error responses. But that was after I had gotten the error response.
So, I thought I could just purge the cache via the CLI. So I ran purge req.http.host == www.mysite.com, then hit refresh on the page, and that didn't seem to work. I'm still getting 503 errors. And looking at the varnishstat -1 output, it's not that the backends are failing as was suggested in some other help topics. The components seem to all be working, there's just something up and I'm unsure of how to troubleshoot this more.
Any help would be appreciated!
I'm running this on Debian, with the Mercury stack, and Drupal 6.x.
Update: It turns out this was caused by the Feeds module maxing out the number of nested function calls allowed, which caused a segmentation fault in the web server, which caused the request from Varnish to fail. God bless xdebug. Feel free to delete this as it turns out this wasn't a Mercury issue after all.
Though, it should be noted for future reference, that varnishlog is useful because it shows where in the request pipeline the error is occurring, and if it occurs after an X-Forward header, it's likely a subcomponent of the Mercury stack, not Varnish.
Comments
Can you get pages to load by
Can you get pages to load by going to the site on :8080 (or whatever port Apache is configured to listen on)?
I couldn't, no. That's one
I couldn't, no. That's one thing that tipped me off to it being an Apache, not Varnish, issue. Pages were coming up blank when I hit 8080 (lots of ports in this setup, so it took me a bit to figure out how everything was working).
Once I fixed the issue related to the Feeds module (I updated my first post once I fixed it with the details), everything worked and Varnish is back to making the site load like lightning.
Thanks for the quick reply, though. This site's a great resource.