[ClusterLabs] Position of pacemaker in today's HA world

[Valentin Vidic]

On Fri, Oct 05, 2018 at 11:34:10AM -0500, Ken Gaillot wrote:
> The next big challenge is that high availability is becoming a subset
> of the "orchestration" space in terms of how we fit into IT
> departments. Systemd and Kubernetes are the clear leaders in service
> orchestration today and likely will be for a long while. Other forms of
> orchestration such as Ansible are also highly relevant. Tighter
> integration with these would go a long way toward establishing
> longevity.

Kubernetes seems to be mostly about stateless services and it kind of
expects you have some external highly available data store.  You can
either buy that data store from your cloud provider or try to make it
yourself, for example using Pacemaker and Galera. Maybe some agents for
registering Pacemaker resources in the Kubernetes etcd or consul would
be useful to connect the two worlds.

On the other side, the big players seem to have settled on using
distributed consensus protocols (Paxos, Raft, Zab) for building
replicated state machines across multiple data centers (or even
continents). It would be an interesting experiment if we could easily
hook up Pacemaker with Zookeeper - selecting a DC node would require
just creating a znode file. Master node can than store the cluster
configuration as another znode and also ask other nodes to do some work
through a job queue. On a global scale this would be quite slow (5-10
changes per second) and node fencing is not available but for some types
of resources it might be useful.

Some more reading material on the topic for the weekend :)

https://landing.google.com/sre/book/chapters/managing-critical-state.html
https://www.infoq.com/articles/cap-twelve-years-later-how-the-rules-have-changed

-- 
Valentin