Viewstamped replication(VR) is a replication technique that takes care of failures when one or more nodes end up crashing in a cluster. It works as a wrapper on top of a non-distributed system & allows the underlying business logic to be applied independently while the protocol itself takes care of replication. The protocol was introduced in the paper and then was revised with a set of optimizations under a new paper known as Viewstamped replication revisited.
