503s and FetchError - V3.0.7

[Jason Price]

Party Line: varnish 3.x is EOL.  Move to Varnish 4

Looks like you're logging the client side in varnishlog.  Try to catch one
of the Backend transactions that does this.  You'll have to use varnishlog
without either -c or -b or -m specified, and trawl through it manually.

varnishadm debug.health

might help as well.  If all backends in a director are unhealthy, varnish
will serve an immediate 503 if the request goes to that director.

-Jason

On Wed, Oct 14, 2015 at 3:54 PM, Vlad Rusu <vlad.rusu at cloudtroopers.ro>
wrote:

> Good day everyone,
>
> I am trying to get to the bottom of the 503s sporadically logged by our
> Varnish servers. During monitoring, it all comes down to monitoring the
> state of my backends ++ varnishlog.
>
> Most of the 503s come with a FetchError “backend write error: 0 (Success)”
> — and I can’t seem to find anything on the internet to describe what this
> might mean.
>
> —> FetchError   c backend write error: 0 (Success) <—
>
> Also, none of the relevant counters in varnishstat are showing any
> increase (i.e. backend_unhealthy, backend_busy, backend_fail,
> fetch_failed..)
>
> For that same request, looking at ReqEnd, it doesn’t look to me like any
> timeout was reached (like connect_timeout, first_byte_timeout, between_bytes_timeout,
> ..)
>
> —> ReqEnd       c 221990096 1444847550.110866785 1444847550.116131306
> 0.000048876 0.000905752 0.004358768 <—
>
>
> *Any chance we could get a list of possible FetchError messages and what
> they might mean — at least something to put us on a right track? Would
> surely help knowing where to start looking, especially when everything
> seems fine.*
>
> Also, in this FetcError scenario, *is it expected to see retries from
> Varnish?* If so, why would Varnish only retry some of the backends in a
> director and not all of them (or the .retries value)?
>
>    44 VCL_return   c hash
>    44 VCL_call     c pass pass
>    44 Backend      c 20 drpau_ssl_director drpau34ssl
>    44 FetchError   c backend write error: 0 (Success)
>    44 Backend      c 51 drpau_ssl_director drpau31ssl
>    44 FetchError   c backend write error: 0 (Success)
>    44 VCL_call     c error deliver
>    44 VCL_call     c deliver deliver
>    44 TxProtocol   c HTTP/1.1
>    44 TxStatus     c 503
>    44 TxResponse   c Service Unavailable
>
> Should these be reflected in varnishstat’s “backend_retry”?
>
> Thank you guys!
> Vlad Rusu
>
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>
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