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Re: Rambling apt-get ideas

On Fri, Dec 29, 2000 at 11:11:01PM +0100, mechanix@digibel.org wrote:

> 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.

I still disagree.  Multicast is the wrong solution.  Multicast data is
basically equivalent to a cache with zero object TTL.  Packets (objects) are
stored (by a network device) until a client needs them (immediately), at which
point they are served (multicasted/broadcasted) and expired (discarded).  Why
not replace this with a _real_ cache, which can store objects for a
user-definable period of time, allowing for later operations to benefit from
the cache?

It _might_ be useful to use multicast for a system which would trigger a bunch
of daemons to all download the same data from the cache, but even this is
doubtful.  Unless you are dealing with many thousands of clients, the overhead
for sending individually-addressed packets to the clients is minimal.

This is definitely a "pull" problem rather than a "push" problem.  Say a system
is being installed in a new location, which has network connectivity, but no
user consoles (yet).  Why should the admin have to find a live terminal in
order to tell the server to initiate a multicast installation?  Why not just
have the bootstrap disk fetch the necessary data?

> 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).

Better to separate automatic system building/configuration (a very hard problem
with relatively little progress) from efficient hierarchical file distribution
(an easier problem, with many good, stable tools already released).

> 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!

Also consider:

You boot with the floppy that configures the network, start downloading files
over TCP, the workstations install them.
Voilà!  You just installed an entire network!

This approach will also work with heterogenous hardware, which is an issue in
a majority of enterprises.

 - mdz

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