503 due to content-length error? microwave issue?

Alan Dixon alan.g.dixon at gmail.com
Tue Nov 9 19:05:50 CET 2010

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.

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