Weird Varnish 503 error - what does this mean?

varnish
Donny picture Donny · Jul 10, 2012 · Viewed 64.6k times · Source

My online whiteboard application has been working previously, but for whatever reason, it no longer works. Now it shows a 503 Varnish cache error as seen here: http://grab.by/eFHG

Do you happen to know where I should start to look to try to resolve this issue?

Thanks! Donny

Answer

Gauthier Delacroix picture Gauthier Delacroix · Jul 13, 2012

This error means that Varnish had no response (even not an HTTP error) from the backend within the timeout limit.

You can troubleshoot that in many ways :

  • On the backend : do you see requests from Varnish in your webserver log ?

  • On Varnish server : Run varnishlog and check the request process. You should have events in this order : RxRequest > TxRequest > RxResponse > TxResponse. Your problem is between TxRequest (request sent to backend) and RxResponse (response received from backend).

  • On your Varnish server try connecting on the backend using telnet (telnet ). Does it connect ? If it does, try sending a request (e.g. "GET / "). Do you receive a response ?

Probable causes could be : firewall/selinux blocking between varnish & backend, bad varnish or backend web server config (are backend address & port sync ?), webserver stopped, ...

Related questions

Configure multiple sites with Varnish

We have a server which needs to serve multiple domains though varnish e.g. example1.com, example2.com and example3.com Our current .vcl file looks like this: sub vcl_recv { set req.http.Host = "example1.com"; lookup; } How do …

Read More
Error 503 Backend fetch failed

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?

Read More
How to clear complete cache in Varnish?

I'm looking for a way to clear the cache for all domains and all URLs in Varnish. Currently, I would need to issue individual commands for each URLs, for example: curl -X PURGE http://example.com/url1 curl -X PURGE …

Read More