Paxos is a classic consensus algorithm. It solves one narrow but important problem: a group of nodes must agree on one value, even when some nodes crash and messages arrive late, arrive twice, or arrive out of order.

Paxos matters because its ideas show up in many distributed systems:

Paxos also has a reputation for being hard to learn. The protocol is small, but the reason it is safe is not obvious at first.

This chapter starts with the core single-value protocol. Once that is clear, Multi-Paxos and production concerns are much easier to understand.