Error 503 Backend fetch failed

Question

I have this error in my site

Error 503 Backend fetch failed

Backend fetch failed

Guru Meditation:

XID: 526707

Varnish cache server

Anyone know what may be the cause or how to find out what happens?

Answer 1

There's a common reason that varnish returns 503 that is not explained on the varnish error list. I have learnt this from experience.

If your web server is returning 500 error or similar then varnish simply says Error 503 Backend fetch failed.

what you need to do is to always try to fetch without varnish to see if the error is in varnish or the web server. For example if you have a different hostname for the webserver, load that and find the error, if you fix that, then restart varnish and that solves it most of the time.