[openstack-dev] [TripleO] our update story: can people live with it?

Clint Byrum clint at fewbar.com
Fri Jan 24 19:52:47 UTC 2014

Excerpts from Day, Phil's message of 2014-01-24 04:24:11 -0800:
> > >
> > > Cool. I like this a good bit better as it avoids the reboot. Still, this is a rather
> > large amount of data to copy around if I'm only changing a single file in Nova.
> > >
> > 
> > I think in most cases transfer cost is worth it to know you're deploying what
> > you tested. Also it is pretty easy to just do this optimization but still be
> > rsyncing the contents of the image. Instead of downloading the whole thing
> > we could have a box expose the mounted image via rsync and then all of the
> > machines can just rsync changes. Also rsync has a batch mode where if you
> > know for sure the end-state of machines you can pre-calculate that rsync and
> > just ship that. Lots of optimization possible that will work fine in your just-
> > update-one-file scenario.
> > 
> > But really, how much does downtime cost? How much do 10Gb NICs and
> > switches cost?
> > 
> It's not as simple as just saying "buy better hardware" (although I do have a vested interest in that approach ;-)  - on a compute node the Network and Disk bandwidth is already doing useful work for paying customers.   The more overhead you put into that for updates, the more disruptive it becomes.

Agreed. The question becomes whether you should reserve a portion of
your resources for updates or let them push you into over-subscription.
Either way, those are business decisions.

And once we have a working system and we can say "this costs X bitcoins",
we can make a clear justification for somebody to spend developer time
to push X downward.

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