503s for a non-cached host / Re: [SOLVED] Varnish stops waiting backend after 1 second

[Geoff Simmons]

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On 05/13/2016 09:48 AM, Garau Simone wrote:
> 
> I still have an issue I can’t understand: I get some random 503
> from the backend where Varnish isn’t caching. After a couple of
> refresh of the page is properly served.
> 
> The Apache logs shows no activity when Varnish sends a 503, like
> Varnish doesn’t send the request.. Or why isn’t Apache logging?

> *   << BeReq    >> 1115881
[..]
> -   Timestamp      Bereq: 1463124821.994727 0.000229 0.000229 -
> FetchError     http first read error: EOF -   BackendClose   46
> boot.default -   Timestamp      Beresp: 1463124826.994768 5.000270
> 5.000041

FetchError is the critical log entry for a 503 error, and in this case
there was a failure reading the first bytes of the backend response
after very close to 5 seconds.

Looks very much like first_byte_timeout=5s elapsed. Varnish could also
do that on a connection reset, meaning that the connection was closed
by the backend or an intervening network component -- the latter might
explain why Apache doesn't seem to receive the request.

Since the time difference in the Beresp Timestamp is so close to
exactly 5 seconds, I'd suspect that some component has hit a timeout.


HTH,
Geoff
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