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

Clint Byrum clint at fewbar.com
Tue May 30 21:07:52 UTC 2017

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.

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