Re: Avahi support

[Robert McQueen <robert endlessm com>]

(resurrecting this thread from just before I joined the list, apologies 
for breaking the msgids)

Hi Colin,

> Well, things get a lot easier if we assume a smart server like git has.  At a small scale
> it could make sense.  I've just not wanted to really try to do that myself because a protocol
> is tricky to design, although most of it could probably be taken from git.  Plus static webservers
> are very secure.
>
> Though actually, it likely wouldn't be hard to write a webserver that knew how to generate
> ostree objects on demand from the on-disk files (just basically gzipping them).
>
> But for the static approach, the client keeping around the deltas doesn't seem too bad,
> assuming that there's not a lot of version drift.  Say just keep the last delta, or possibly two?

I'm not convinced deltas are the right answer here - my considerations 
for a LAN updater are this:

 - you can assume bandwidth is cheap, because you're on a LAN

 - you can assume load will be small, because you're going to turn this 
on explicitly ("Share updates with friends..."), or if the OS enables 
the feature for you whatever does that can set some resource limits or 
policy if OStree has a mechanism

 - you can't necessarily make assumptions about the versions that other 
people are using because they might not have a connection/source of 
upgrades and you don't know their update frequency - consider a monthly 
"LAN party" where people can bring their systems to upgrade - if you 
miss one/two/N you can never upgrade again?

To me this makes the "slightly less dumb web server that can gzip files 
from your deployment" a far more compelling solution - it's idempotent 
and stateless: you can always guarantee to be able to upgrade any other 
user of a compatible architecture to the OS you're running.

It seems to me like anything based around caching/distributing 
pre-calculated deltas is going to be really fragile because it has to be 
based around assumptions which in my mind aren't safe to make, and it 
creates a management problem (around what deltas do you keep, do you 
have space, for how long, etc or what do you generate at great 
time/cost) which will have a massive effect on whether the entire P2P 
update strategy works in practice.

Cheers,
Rob

........................................................................

Robert McQueen  |  +1.415.413.4159  |  Endless <http://endlessm.com/>