Open Stack

On Wed, Aug 27, 2014 at 11:41:29AM -0400, Zane Bitter wrote:
> On 27/08/14 11:04, Steven Hardy wrote:
> >On Wed, Aug 27, 2014 at 07:54:41PM +0530, Jyoti Ranjan wrote:
> >>    I am little bit skeptical about using Swift for this use case because of
> >>    its eventual consistency issue. I am not sure Swift cluster is good to be
> >>    used for this kind of problem. Please note that Swift cluster may give you
> >>    old data at some point of time.
> >
> >This is probably not a major problem, but it's certainly worth considering.
> >
> >My assumption is that the latency of making the replicas consistent will be
> >small relative to the timeout for things like SoftwareDeployments, so all
> >we need is to ensure that instances  eventually get the new data, act on
> 
> That part is fine, but if they get the new data and then later get the old
> data back again... that would not be so good.

Right, my assumption is that we'd have a version, either directly in the
data being polled or via swift object versioning.  We persist the most
recent metadata inside the instance, so the agent doing the polling just
has to know to ignore any metadata with a version number lower than the
locally stored data.

This does all seem like a fairly convoluted way to work around what are
seemingly mostly database bandwidth issues, but the eventual consistency
thing doesn't seem to be a showstopper afaics, if we go the swift
direction.

Steve