Open Stack

Clint Byrum wrote:
> Excerpts from Chris Dent's message of 2015-11-05 00:08:16 -0800:
>> On Thu, 5 Nov 2015, Robert Collins wrote:
>>
>>> In the session we were told that zookeeper is already used in CI jobs
>>> for ceilometer (was this wrong?) and thats why we figured it made a
>>> sane default for devstack.
>> For clarity: What ceilometer (actually gnocchi) is doing is using tooz
>> in CI (gate-ceilometer-dsvm-integration). And for now it is using
>> redis as that was "simple".
>>
>> Outside of CI it is possible to deploy ceilo, aodh and gnocchi to use
>> tooz for coordinating group partitioning in active-active HA setups
>> and shared locks. Again the standard deploy for that has been to use
>> redis because of availability. It's fairly understood that zookeeper
>> would be more correct but there are packaging concerns.
>>
>
> Redis jettisons all consistency on partitions... It's really ugly:
>
> https://aphyr.com/posts/307-call-me-maybe-redis-redux
>
>      These results are catastrophic. In a partition which lasted for
>      roughly 45% of the test, 45% of acknowledged writes were thrown
>      away. To add insult to injury, Redis preserved all the failed writes
>      in place of the successful ones.
>
> So... yeah. I actually think it is dangerous to have Redis in tooz at
> all. One partition and you have split brains, locks granted to multiple
> places, and basically the pure chaos that you were trying to prevent by
> using a lock in the first place. If you're using redis, the only sane
> thing to do is to shut everything down when there's a partition (which
> is not easy to detect!).

This is where it gets weird, redis, imho, is alot like openstack, alot 
of ways to tweak it, alot of operational modes and a few 
clustering/failover modes.

The one that that I think the above mentions is sentinel:

http://redis.io/topics/sentinel

But from my understanding the following is being created/evolving to 
make this better (to some degree):

http://redis.io/topics/cluster-tutorial

http://redis.io/topics/cluster-spec

Overall maybe we should deprecate the redis driver, and come back to it 
when clustering has been more proven out (afaik redis clustering is 
fairly new); that might be acceptable imho, if we as a community are 
willing to do this.

>
> To contrast this with Zookeeper and Consul:
>
> https://aphyr.com/posts/291-call-me-maybe-zookeeper
> https://aphyr.com/posts/316-call-me-maybe-etcd-and-consul
>
> Even though etcd and consul ended up suffering from stale reads, they
> added pieces to their API that allow fully consistent reads (presumably
> suffering a performance penalty when doing so).
>
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