On 4/10/12 5:36 PM, Justin Santa Barbara wrote:
The immediate use case I have in mind is to support this:
http://wiki.openstack.org/PackageConfigForNova . That design
requires periodic checkins between an instance agent and a nova
driver. It certainly /could/ be implemented using ssh, but I
originally wrote the design imagining there was a ready-made,
standard communication service, and I still think it would be
convenient.
My concern with that proposal is that it starts simple enough, but
then when you want to know e.g. "was the package installed
successfully? is the service healthy?" then you need more and more
complexity i.e. you end up with PlatformLayer, RedDwarf, Heat, Puppet,
Chef or Juju. So putting a small piece of the required functionality
into nova doesn't address your actual use case, which is "I want
configured machines, not just the stock images". It's probably easier
to put that logic into your management system of choice, so nova
shouldn't do it. Am I off base here?
You're not necessarily off base. WMF has some peculiar needs in this
regard because in addition to managing instances with puppet we also
want to use our cloud as a puppet development platform. I've scheduled
a discussion about this:
http://summit.openstack.org/sessions/view/33
It would neither shock nor upset me if at the end of that session we
conclude that I need to just write a private extension for our internal
use. Even if that happens, I'll still need a way for Nova to chat with
instances, though.
Come to think of it, the other session that I have planned
(http://summit.openstack.org/sessions/view/3) is going to trail off at
the end with me saying something like "Now that the volumes are created,
we need to notify existing instances to mount them... somehow." So
that's another use case for having a guest agent with runtime nova
communication.
I continue to suspect that such a service would be widely useful, and
better than leaving every feature to arrange its own communications.
The metadata service is almost what I want, I 'just' need it to be
read/write at runtime.
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