Conveniently this gets tested during every new region launch. Each service is brought online in a sequence, and each service can only use other services running

Conveniently this gets tested during every new region launch. Each service is brought online in a sequence, and each service can only use other services running in the same region, which guarantees that no two services can be mutual startup dependencies. Sometimes region build-outs have to be paused when a circular dependency is discovered that has been introduced since the last region launch!