Ceph

It warns to dout and the logger:
1) when the slave notices the leader is behind by >(mon_lease - latency), or
2) when the leader is ahead of the follower by >latency, or the follower is ahead of the leader by > double latency.
This is all the detection we can do.

It'd be nice to actually handle clock drift, and we could possibly do so, but to make it reliable with proper Paxos guarantees we'd need to switch to relative lease time extensions and it would be a bit of a mess.