High Availability DHCP with relayed subnets on MAAS 3.4/stable

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Hello all,
We have MAAS 3.4/stable (3.4.0-14321-g.1027c7664) deployed to a lab environment as well as starting to roll it out worldwide in production. In the lab we were able to successfully test a full HA setup with 2 region controllers and 2 rack controllers providing load balancing, but most of our environments are small colo datacenter racks where we cannot fit multiple MAAS rack controllers in each physical rack (due to power budget and/or space concerns). Our standard architecture (prior to MAAS) uses IP helpers (to relay DHCP from one colo to another within the same geographic area), and to load balance between 2 in order to provide resilience in case one goes down.

We have MAAS relaying DHCP services from a rack controller in each geographic area and it works well to serve multiple subnets, but unlike in the lab where we were presented with the two drop-down menus to configure primary and secondary, we can’t find a away to add a second rack controller when using relayed DHCP in order to provide high availability.

Is there a way to enable HA DHCP for relayed subnets, or is this restricted to a single rack server in MAAS? If it isn’t restricted, how do we go about enabling it, and if it is, how to we achieve proper HA resiliency?

Thanks!

2

Diving into the CLI documentation, it provides more context than the UI does. In order to accomplish what I’m looking for, I’d have to:

maas $PROFILE vlan update $FABRIC_ID $VLAN_TAG dhcp_on=True \
    primary_rack=$PRIMARY_RACK_CONTROLLER \
    secondary_rack=$SECONDARY_RACK_CONTROLLER 

maas lct vlan update $FABRIC_ID $VLAN_ID_SRC relay_vlan=$VLAN_ID_TARGET

From the looks of this taxonomy, it would seem that both rack controllers would need to exist on $VLAN_ID_SRC as there doesn’t seem to be a way to add a second target. On the network side, we have the same VLAN globally for our MAAS infra rollout, but MAAS assigns each switch it’s connected to a new fabric with a default VLAN under it.

Does this mean that a set of HA rack controllers both need to be connected to the same switch?