openstack team mailing list archive

[Soren Hansen <soren@xxxxxxxxxxx>]

2011/7/7 Jay Pipes <jaypipes@xxxxxxxxx>:
> Multiple zones is currently only supported in the OpenStack API, and
> the question has been raised whether effort should be expended to get
> parity in the EC2 API for this. The problem with the EC2 API is that
> we do not have control over the instance identifiers -- they are an 8
> character text string. We would still need to map the EC2 instance
> identifier to some globally unique identifier (like a UUID), but the
> solutions for how to do this aren't pretty (see
> http://etherpad.openstack.org/EC2UUID).

I don't particularly like the idea of maintaining a mapping table. If
such a method is to be guaranteed to function, we need something that
can reliably assign EC2-compatible ID's corresponding to the UUID's
without collisions. If we can come up with such a method anyway, why
use UUID's to begin with?

(For the record, I do believe we *can* come up with such a method. I
raised this point in one of the (several) disucssions we've had on the
subject of ID's, but the ability to assign an unlimited amount of
non-colliding ID's perpetually autonomously took precedence)

I think the only sensible route is truncating (or by other means
reducing) the UUIDs to 32 bits (or revisit (again) the choice of
UUID's, of course).
With a 32 bit key space, a user with 10000 active objects of the same
type (so in the same key space) will have a 1% chance of having
colliding ID's. With ~78000 objects, we're at 50%. I guess that's a
risk we'll have to live with. The tricky part is figuring out how to
handle the collisions when they actually arise.

-- 
Soren Hansen        | http://linux2go.dk/
Ubuntu Developer    | http://www.ubuntu.com/
OpenStack Developer | http://www.openstack.org/