[2.x, enhacement] Deleting a controller should not block on it being the primary rack controller

[Mark Shuttleworth]

I am unable to delete a controller because 'It is the primary controller on VLAN foo.bar'. That makes no sense, since controllers are HA, and there is another controller on the same VLAN, so services will/should continue without interruption.

While it is useful to have a sense of controllers which are well-connected to a fabric, it makes no sense to manually "lock" a controller to a fabric. So I would say that a fabric summary page should show:

 * which controllers can see that fabric and therefor provide HA services
 * if there is a ranking of controllers

Any ranking could be represented with a number between 1 and 5 with 1 being preferred over 2 etc.

[Mark Shuttleworth (sabdfl)]

Any comment on this bug, please? I need to replace the controller and cannot delete the old one.

[Blake Rouse (blake-rouse)]

At the moment we have enabled only manual HA for isc-dhcp-server. This requires the user to manually change the primary and secondary rack controllers for a DHCP server. The lease state is synchronized between each DHCP server, switching those dynamically can cause loss of leases and duplicate IP address assignments. That is one of the reasons we always made the selection of the primary and secondary isc-dhcp-server a manual choice.

MAAS DHCP also is in 100/0 mode for isc-dhcp-server. Meaning the primary rack controller serves all DHCP requests, the secondary is only used when the primary goes down. Removing the primary rack controller of a VLAN and switching the secondary to primary might not be something the administrator was aware would occur from deleting the rack controller.

On the VLAN details page you can switch the rack controller from being the primary of the VLAN so you can delete the rack controller.

On the VLAN details page it does provide a list of rack controllers that have access to that VLAN. Any one of this rack controllers can manage DHCP for that VLAN. As for ranking any rack controller could manage the DHCP server, we currently leave that up to an administrator to make that choice. In the future MAAS could use more information like the link speed, location in the rack (relative to the machines connected to the VLAN), MAAS being on the switch, etc. to determine a ranking of which rack controllers could better manage the VLAN.