Comment 1 for bug 1702096

I agree "manual control of service interfaces" would very nice to have, but the scope of that is too large for a bug fix.

As for the symptom being seen here, we recently fixed bug #1695083 (for inclusion in MAAS 2.2.1), which should provide better behavior for NTP server selection. Previously, MAAS might have choose any address on the box as the NTP endpoint. With that fix, the pool of possible NTP server addresses is limited to "managed interfaces" (IP addresses on rack interfaces with DHCP enabled). So it should solve the problem you're seeing, unless you also have MAAS DHCP managing lxdbr0 (in which case, roll the dice).

Bug #1695937 captures the additional concern that you might have two mutually unreachable VLANs on a rack controller. But that fix has a larger scope, so was not included in the fix for bug #1695083.