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Re: Rambling apt-get ideas



On Thu, Dec 28, 2000 at 06:08:16PM -0500, Matt Zimmerman wrote:
> On Thu, Dec 28, 2000 at 08:22:52AM -0600, Vince Mulhollon wrote:
> 
> > My point being, that yes I already use squid as a proxy server for a whole
> > network of apt-geting debian boxes and after only a little work it works
> > OK, but something using IP multicast would be better due to lower network
> > utilization.  True, doing multiple simultaneous upgrades means eventually
> > an upgrade would kill all the machines simultaneously, and my high end
> > pentiums are going to decompress the gzip parts much faster than my old
> > 386s, although there are probably ways around that, just because all the
> > .debs are distributed all at once in one multicast burst doesn't mean they
> > have to be installed all at once.  Anyway, squid does not do IP multicast
> > to multiple simultaneous clients, last time I checked.  Another cool
> > ability of an integrated cache would be that the "fetching" machine could
> > maintain a list of all the machines it pushed the new .deb to, and when all
> > the "client" machines have a copy of the new .deb, clear it from the cache.
> > With a squid solution, squid has to guess if its OK to clear the cached
> > .deb based upon access time, size, etc.  Even worse, my squid only caches
> > files less than 8 megs, thus each machine downloads its own copy of emacs,
> > etc.  A cache for general web use "works", but a cache designed
> > specifically for .deb packages would work better.
> 
> There is very little tuning you could do for a general-purpose web cache in
> order to support .debs that would not be generally applicable to other
> situations.  Rather than creating a new caching proxy for .debs, why not
> improve squid to do what you want?  That way, other applications (which may or
> may not exist yet) can also benefit.  Squid does in fact use multicast, but
> only for ICP (and thus only for very small objects).  I think you will find
> that IP multicast is not particularly suited to this task.  In order to avoid
> overflowing socket buffers on the client, the server would have to multicast
> its data only as fast as the slowest client.  Not only does this cause a
> performance bottleneck, but it is tricky to detect how fast the client can
> receive data, and adjust accordingly.  If the systems are not all on the same
> LAN, the server must take into account network congestion, etc.  This is what
> protocols like RTSP try to do.  Where real-time content delivery is not an
> issue, TCP does a much better job of responding to changing network conditions.
> Of course, if all of the systems are on the same LAN, you could use real link
> layer broadcast instead of IP multicast.
> 
> The issue of maximum object size is a configuration issue.  The ability to be
> smarter about particular object types sounds like a good idea for a squid
> enhancement.
> 

Why not look at this from a different perspective? I don't know if it may be
useful or not for upgrading machines, but the multicast server would be a
very nice thing for mass installations.
Image large computer rooms at a lan with (usually) uniform hardware. If there
was a package (say apt-getd) that could be installed on one, already
running box, which lets you make a special boot disk. The machine that runs
apt-getd has a way to get to a debian archive (be it local mirror, a set of
cdroms - this would probably be a bit harder with cd swapping - or a mirror
on the larger network that it is connected to).
You boot with the floppy that configures the network, apt-getd starts
spawning multicast packets, the workstations pick them up and install them.
Voilà! You just installed an entire network!
This would be especially useful for universities/colleges. In fact, a friend
of mine is doing a similar thing for his thesis - only he uses a 'Ghost'
approach - the 'mother server' has an installed disk which gets multicast to
the clients. This *was* on request of the college he's studying at -
currently they have to take an installed harddrive, open the pc case and
install it that way (the commercial 'Ghost' program seems to have a problem
with their hardware).

Regards,

Filip

-- 
"The nice thing about Windows is - It does not just crash, it displays a
dialog box and lets you press 'OK' first."
	-- Arno Schaefer

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