Notify when members in rota do not have notification modes set

[dannykopping]

We recently encountered a situation where a notification got escalated from L1 (engineers) to L2 (managers) due to the alert not being acknowledged. The L2 contact did not have any notification mode set for their Important messages due to an oversight, and the escalation did not reach them. The alert then escalated to L3 (directors), which was unfortunate.

I propose that oncall should send a notification when any members in the rota do not have notification modes set, in a similar fashion to how the notifications for no-one being actively on-call at the moment works. This would have helped us preemptively address this misconfiguration, and avoid an unnecessary escalation to very senior staff.

[Matvey-Kuk]

I agree, also faced this problem.

[joeyorlando]

closing as duplicate of #1511