[Leases] are a nearly ubiquitous, go-to, mutual exclusion me...

Leases are a nearly ubiquitous, go-to, mutual exclusion mechanism in distributed systems. The core idea is simple: have a client lease the right to exclude other clients for a period of time, and allow them to periodically renew their lease to keep excluding others. Leases, unlike more naive locks, allow the system to recover if a client fails while holding onto exclusivity: the lease isn’t renewed, it times out, and other clients are allowed to play. It’s this fault tolerance property that makes leases so popular.

Did you notice those words a period of time? Leases make a very specific assumption: that the lease provider’s clock moves at about the same speed as the lease holder’s clock.