Paxos
maang.io System Design Series
Paxos solves the hardest problem in distributed systems: getting unreliable machines to agree on one value, provably, even as messages are lost, delayed, or reordered. Its safety rests on one fact — any two majorities overlap — which forces every later proposer to honor an already-chosen value. Multi-Paxos extends it into the replicated log behind systems like Spanner and Chubby.
This deep dive comes in three parts:
- Foundations & Core Concepts — the roles, the two-phase protocol, and why consensus is hard.
- Internals — acceptor state, the safety proof, dueling proposers, and Multi-Paxos, with worked numbers.
- Interview — Staff/Principal Q&A: safety vs liveness, quorum math, and Paxos vs Raft.