503 due to content-length error? microwave issue?

Alan Dixon alan.g.dixon at gmail.com
Wed Nov 10 15:55:43 CET 2010

Okay, here's the answer: the problem was solved by the user's ISP:
they just lowered the MTU.

Conclusion: adding varnish can create subtle network problems [not
unique to varnish - also true of any front end proxy or ssl].

Not varnish's fault or problem, but good to know, and would be even
better if it were easier to debug.

 - Alan

On Tue, Nov 9, 2010 at 1:05 PM, Alan Dixon <alan.g.dixon at gmail.com> wrote:
> I have nicely functioning varnish instance in front of a
> drupal/civicrm website, running on debian/lenny (varnish-2.1.3 SVN ).
> I have one user who is unable to POST (though maybe by AJAX . not sure
> ...?). When she tries, she gets the varnish 503, which doesn't help
> too much.
> When I look at the apache logs, I see that the response to her POST is
> a 200 with a reasonable amount of content, whereas I get a 302,
> correctly redirecting me after a successful post.  So it might be that
> she's getting some kind of form invalid type of response, but varnish
> isn't displaying it for some reason?
> But here's another clue: she's using a microwave tower for her ISP.
> I'm thinking that maybe this is doing something funny with the
> packets, and so the content-length of the submission or reply from
> apache is wrong and apache is more forgiving than varnish. Does that
> make sense?
> The varnish log shows identical behaviour with my sucessful post up
> until the end of the TxHeaders to the apache backend. At that point,
> she gets
>   16 FetchError   c backend write error: 11
>   17 BackendClose b default
> whereas I get the answer back to varnish who then sends it on to me
> properly. In both cases, varnish is correctly pass'ing the request to
> the apache backend, and the headers look almost identical (we're both
> running chrome - she's on windows and I'm on linux). Her content
> length is almost the same, with the same content-type/boundary.
> Any clues?
> --
> Alan Dixon, Web Developer
> Drupal and CiviCRM for Canadian nonprofits.
> http://blackflysolutions.ca/

Alan Dixon, Web Developer

Drupal and CiviCRM for Canadian nonprofits.

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