[openstack-dev] [Nova] bp proposal: discovery of peer instances through metadata service

Justin Santa Barbara justin at fathomdb.com
Mon Jan 27 14:52:29 UTC 2014

Day, Phil wrote:

> >> We already have a mechanism now where an instance can push metadata as
> >> a way of Windows instances sharing their passwords - so maybe this could
> >> build on that somehow - for example each instance pushes the data its
> >> willing to share with other instances owned by the same tenant ?
> >
> > I do like that and think it would be very cool, but it is much more
> complex to
> > implement I think.
> I don't think its that complicated - just needs one extra attribute stored
> per instance (for example into instance_system_metadata) which allows the
> instance to be included in the list

Ah - OK, I think I better understand what you're proposing, and I do like
it.  The hardest bit of having the metadata store be full read/write would
be defining what is and is not allowed (rate-limits, size-limits, etc).  I
worry that you end up with a new key-value store, and with per-instance
credentials.  That would be a separate discussion: this blueprint is trying
to provide a focused replacement for multicast discovery for the cloud.

But: thank you for reminding me about the Windows password though...  It
may provide a reasonable model:

We would have a new endpoint, say 'discovery'.  An instance can POST a
single string value to the endpoint.  A GET on the endpoint will return any
values posted by all instances in the same project.

One key only; name not publicly exposed ('discovery_datum'?); 255 bytes of
value only.

I expect most instances will just post their IPs, but I expect other uses
will be found.

If I provided a patch that worked in this way, would you/others be on-board?

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstack.org/pipermail/openstack-dev/attachments/20140127/d2619c86/attachment.html>

More information about the OpenStack-dev mailing list