Comparison
FailbackvsFailover
Failback
the original site came back and moving home turned out to be harder than the failover was, because the standby now holds the newer data.
Returning to the primary after a failover, which requires reconciling whatever the secondary accepted while the primary was away. It is the half of disaster recovery that is routinely undocumented, and it is usually the riskier half, because it is planned rather than forced and everyone is tired. Many teams deliberately do not fail back, and simply treat the secondary as the new primary until the next event.
Full entry →Failover
the primary stopped answering and something promoted a replica, and now you find out how much of the last few seconds you lost.
Promoting a replica to leader when the current leader is deemed dead. Under asynchronous replication it loses any unreplicated writes; under synchronous it may refuse to proceed. The hard part is the deeming: too eager and you failover on a network blip, too slow and the outage is the timeout.
Full entry →