Re: Problem with apache proxying between domains

[Nivedita Singhvi <niv@us.ibm.com>]

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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