Understanding Consensus: From Raft to PoW in Blockchain

0 What is Consensus?

Consensus means a shared agreement, the process by which participants reach a common decision.

1 From Single Machine to Cluster

Two reasons to move to clusters: performance limits and reliability concerns; the latter leads to the need for consensus among replicas.

2 Multi‑Replica Consensus

In a distributed system, achieving agreement can rely on trust, voting, or more complex protocols.

3 Challenge 1: System Crashes

Crash fault tolerance (CFT) ensures the system continues operating despite network, disk, or server failures.

4 Solution: Paxos and Raft

Paxos (1990) and Raft (2013) are CFT algorithms that tolerate up to half faulty nodes. Paxos uses proposers, acceptors, learners; Raft uses leader, follower, candidate and log replication.

5 Challenge 2: Byzantine Nodes

In consortium environments, malicious nodes can disrupt consensus, requiring Byzantine fault tolerance (BFT).

6 Solution: PBFT

Practical Byzantine Fault Tolerance (PBFT) achieves consensus with three‑phase commits, tolerating up to one‑third malicious nodes.

7 Challenge 3: Massive Public Nodes

Public blockchains need algorithms that scale to thousands of nodes, which PBFT cannot handle.

8 Solution: PoW and PoS

Proof‑of‑Work (PoW) uses computational puzzles (e.g., Bitcoin) while Proof‑of‑Stake (PoS) selects validators based on token holdings; both provide consensus for open networks.

9 Summary

Consensus is a core topic in distributed systems and blockchain. We covered Raft and Paxos for private settings, PBFT for consortium, and PoW/PoS for public chains.