Distributed consensus, the ability to reach agreement in the face of failures and asynchrony,
is a fundamental primitive for constructing reliable distributed systems from unreliable
components. The Paxos algorithm is synonymous with distributed consensus, yet it performs
poorly in practice and is famously difficult to understand. In this paper, we re-examine the
foundations of distributed consensus. We derive an abstract solution to consensus, which
utilises immutable state for intuitive reasoning about safety. We prove that our abstract�…