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From Michal Mertl <michal.me...@i.cz>
Subject Re: problems with mod_proxy and mod_cache on 2.X
Date Mon, 28 Mar 2005 14:58:07 GMT
Graham Leggett wrote:
> Michal Mertl wrote:
> 
> > I'm developping caching proxy server with antivirus. The best/cleanest
> > solution seems to me apache2 + mod_clamav. I had to fix mod_clamav
> > substantialy but now I stumbled across some bug in mod_proxy. I know
> > about several situations where the pages get loaded wrongly regardless
> > of the browser and or apache2 version (2.0.53 or 2.1.4). Fortunately the
> > situation is quite rare.
> > 
> > The best example is http://www.vtipky.cz/. The page loads well with
> > Apache1.3 base proxy.
> 
> Can you send more details on the problem that you found?

I really don't know exactly. I thought the problem is much more
widespread but now it seems it's quite rare.

The problem seems to be in particular site (webserver) which responds
from time to time to the same request differently. I've never seen error
message in the browser when going direct of through Apache 1.3 based
proxy. I suspect it was just luck I didn't notice it with 1.3 now. On
the other hand I've seen it when using FreeBSD fetch utility (similar to
wget) - it also fails the link from time to time with "unknown error"
message.

Failing URL is for example this one (it's random):

http://adx1.adrenaline.cz/adrun.dll?action=1&id=4766&target=_top&border=1&bgcolor=ffffff&link=0000FF&ref=&rnd=662405

It's tempting to say it's the server's fault but because it doesn't
appear in direct connection it's unfortunate. I managed to get tcpdump
of a failed request with fetch. It really is server's fault - instead of
replying with the data it just closes the connection. A second later the
same request works. It seems the browser must react to the broken server
by retrying while mod_proxy sends to the client the Bad Gateway error
(which seems correct).

The bad thing is that the server in question is (I thing) pretty heavily
used on some important pages on the Czech Internet. Unfortunately I
don't browse much in there but the users will surely do so I can't be
sure how often the problem appears. The server is an advertising server.

I'll check with squid - if it sends error to the client I would say it's
a server's problem and give up on the issue. 


The other issue happens probably even more seldomly. It may be even
browser bug but it doesn't happen when going direct or with Apache 1.3
based proxy either. The problem appears only with Mozilla with proxy
configured as HTTP 1.1 and pipelining enabled. Because it's be default
off I don't think it's as bad as the first one (would affect small
number of users).

The problem appears when I go to URL
http://tools.cisco.com/Support/Fusion/FusionHome.do

You need to be registered Cisco customer (partner?) to be able to access
it. It's normal page with several images and stuff and the problem is
that several of the images don't load. It happens always. When I sniffed
the traffic I didn't see the browser asking for the image even so it
looks like an issue in the browser. Still why doesn't it happen with
direct connection?

Thanks

Michal



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