Hello!

On Sat, May 11, 2013 at 04:13:38PM +1000, Daniel Black wrote:

[...]

> > A request for /img/file_doesnt_exist.jpg results in the backend server
> > (192.168.129.90) getting continuous requests for the same file (which
> > doesn't exist there either so 404 each time), while the original
> > requester waits and nginx keeps asking the backend the same.
> >
> > I'm using the nginx-1.4.1 from the debian squeeze repository.

[...]

> > server 173.230.136.6 backup;

[...]

> > proxy_next_upstream error timeout invalid_header http_500 http_502
> > http_503 http_504 http_404;

What you describe looks very familiar - there was such a bug which
manifested itself with backup servers and proxy_next_upstream
http_404. It was fixed in 1.3.0/1.2.1 though:


*) Bugfix: nginx might loop infinitely over backends if the
"proxy_next_upstream" directive with the "http_404" parameter was
used and there were backup servers specified in an upstream block.

Are you sure you are using 1.4.1 on your frontend (note: it's
usually not enough to check version of nginx binary on disk, as
running nginx binary may be different)? Could you please provide
frontend's debug log?

--
Maxim Dounin
http://nginx.org/en/donation.html

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