The many faces of consensus in distributed systems

Known results regarding consensus among processors are surveyed and related to practice. The ideas embodied in the various proofs are explained. The goal is to give practitioners some sense of the system hardware and software guarantees that are required to achieve a given level of reliability and performance. The survey focuses on two categories of failures: fail-stop failures, which occur when processors fail by stopping; and Byzantine failures, which occur when processors fail by acting maliciously