feature: support multiple regiond endpoints

[Dmitrii Shcherbakov]

Currently MAAS client library only supports specifying a single target region controller endpoint.

For non-shared-L2 scenarios, however, there are multiple endpoints on different subnets without a shared VIP to hide them.

It should be possible to specify multiple target endpoints in a client library similar to how libpq handles this with PostgreSQL 10 (see https://bugs.launchpad.net/maas/+bug/1791957).

The problem is that MAAS is the first thing to be deployed on a given OAM network and there are no load-balancers or other infrastructure to provide means of proper handling of multi-endpoint scenarios.

Any python software that uses maas client would benefit from the multi-endpoint connection logic.

A specific example would be charm-hacluster which is used to manage address records with 0 TTL in MAAS in order to solve the multi-endpoint problem for MAAS API services. It does solve a problem by creating those records but it cannot connect to multiple MAAS region endpoints by using MAAS client as it expects a single target endpoint.

https://github.com/openstack/charm-hacluster/blob/stable/18.08/ocf/maas/maas_dns.py#L60-L66
https://github.com/openstack/charm-hacluster/blob/stable/18.08/ocf/maas/dns

An interim solution for this charm would be to deploy haproxy on every unit and use a localhost MAAS URL:

client -> http://localhost:5240/MAAS -> haproxy -> multiple maas region endpoints

The charm would have to keep in mind that openstack API charms already deploy haproxy so it would have to use a separate config file and systemd unit to create a localhost load-balancer.

[James Page (james-page)]

I think we discussed this last week (or the one before); The approach the charms take to HA in non-shared l2 deployments is to use DNS-HA for the deployment; MAAS could take the same approach, providing a single managed DNS entry based on availability for clients to connect to.

Then we're not just implementing client-side loadbalancing in the hacluster charm.

[Adam Collard (adam-collard)]

This bug has not seen any activity in the last 6 months, so it is being automatically closed.

If you are still experiencing this issue, please feel free to re-open.

MAAS Team

[Alberto Donato (ack)]

Thanks for your feature request, please could you start a thread over on our Discourse (https://discourse.maas.io/c/features) to discuss the feature?

[Dmitrii Shcherbakov (dmitriis)]

https://discourse.maas.io/t/support-multiple-regiond-endpoints-in-maas-client/1014