Re: Problem with apache proxying between domains

[Andrew Athan <aathan-xen-1542@cloakmail.com>]

What's the equivalent of strace on Windows XP?

:-)

I can strace the two apache processes on the Linux hosts, but not sure I 
can get useful information about the quicktime plugin in the browser.

By the way, dom1 is using swap which is an LVM volume in dom0.  Could 
there be some kind of deadlock in which dom0's apache is blocking on a 
network read which dom1 cannot service because it needs swap, which dom0 
cannot supply via LVM because the dom0 inter-domain stuff is "stuck" 
trying to service the apache inter-domain network request ??

I needed to make progress, so I have punted on inter-domain apache 
proxying for now.  However, I can set up a test config easily enough if 
that is of interest to the group.  The missing packets are somewhat 
worrisome to me, since I would have thought that inter-domain 
communication was lossless.

A.

Nivedita Singhvi wrote:

> Andrew Athan wrote:
>
>> The attached network sniff header lines from Ethereal show the
>> communication between 216.254.100.240 (browser) and 216.254.100.205
>> (dom0) which proxies to 216.254.100.181 (dom1).  You will see that we go
>> to a ZeroWindow condition with about 3 Megs transferred out of the dom0
>> proxy.  At the tail end -- the TCP connection is then kept alive, but
>> the QuickTime plugin never becomes "enabled" and can't play the movie.
>
>
> Can you attach to the process via strace or something and check
> what it's doing? Is it getting scheduled or waiting on IO?
> Since it keepalives successfully, I'm assuming your interface
> hasn't gone down. Also, check for a memory failure - could be
> a mem leak.
>
>> Fetching the same URL via CURL on the Windows host, dom0 host, or a
>> separate physical linux host works fine.  I also created a separate
>> Apache instance on a physically separate linux host, with the exact same
>> Rewrite rules.  Fetching the movie through this proxy works fine in both
>> the QuickTime plugin AND CURL.  I did this to eliminate the possibility
>> of some basic incompatibility between mod_proxy/mod_rewrite and
>> quicktime movies fetched by the quicktime browser plugin.
>
>
> It does look like reading process stops reading. Did you
> alter the default socket buffer sizes, at all, btw?
>
>> I have played with the ProxyIOBufferSize and ProxyBufferSize parameters
>> in the apache isntance in dom0, and have also tried various combinations
>> of bvt weights, warpback, etc.
>>
>> Should I try to capture a sniff of xen-br0 during this interchage?  Will
>> that help?  WHen I tried this I think I only got partial data, perhaps
>> because of the xen domain scheduling causing missed packets.
>
>
> You do seem to be missing packets in your trace as well.
>
> netstat -tan
> netstat -s
> ifconfig -a
> /proc/slabinfo
> vmstat
>
> would be useful on both dom0 and of course, dom1..
>
> thanks,
> Nivedita
>
>
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