[openstack-dev] [Keystone] Cockroachdb for Keystone Multi-master

Mike Bayer mbayer at redhat.com
Thu Jun 1 03:06:23 UTC 2017

On 05/30/2017 09:06 PM, Jay Pipes wrote:
> On 05/30/2017 05:07 PM, Clint Byrum wrote:
>> Excerpts from Jay Pipes's message of 2017-05-30 14:52:01 -0400:
>>> Sorry for the delay in getting back on this... comments inline.
>>> On 05/18/2017 06:13 PM, Adrian Turjak wrote:
>>>> Hello fellow OpenStackers,
>>>> For the last while I've been looking at options for multi-region
>>>> multi-master Keystone, as well as multi-master for other services I've
>>>> been developing and one thing that always came up was there aren't many
>>>> truly good options for a true multi-master backend.
>>> Not sure whether you've looked into Galera? We had a geo-distributed
>>> 12-site Galera cluster servicing our Keystone assignment/identity
>>> information WAN-replicated. Worked a charm for us at AT&T. Much easier
>>> to administer than master-slave replication topologies and the
>>> performance (yes, even over WAN links) of the ws-rep replication was
>>> excellent. And yes, I'm aware Galera doesn't have complete snapshot
>>> isolation support, but for Keystone's workloads (heavy, heavy read, very
>>> little write) it is indeed ideal.
>> This has not been my experience.
>> We had a 3 site, 9 node global cluster and it was _extremely_ sensitive
>> to latency. We'd lose even read ability whenever we had a latency storm
>> due to quorum problems.
>> Our sites were London, Dallas, and Sydney, so it was pretty common for
>> there to be latency between any of them.
>> I lost track of it after some reorgs, but I believe the solution was
>> to just have a single site 3-node galera for writes, and then use async
>> replication for reads. We even helped land patches in Keystone to allow
>> split read/write host configuration.
> Interesting, thanks for the info. Can I ask, were you using the Galera 
> cluster for read-heavy data like Keystone identity/assignment storage? 
> Or did you have write-heavy data mixed in (like Keystone's old UUID 
> token storage...)

I'd also throw in, there's lots of versions of Galera with different 
bugfixes / improvements as we go along, not to mention configuration 
settings.... if Jay observes it working great on a distributed cluster 
and Clint observes it working terribly, it could be that these were not 
the same Galera versions being used.

> It should be noted that CockroachDB's documentation specifically calls 
> out that it is extremely sensitive to latency due to the way it measures 
> clock skew... so might not be suitable for WAN-separated clusters?
> Best,
> -jay
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