Consensus and Replication

reading · we frame, you read MIT or the canonical taught · we author, no canonical fits ↺ spirals back to earlier lessons

Course locked

Complete Foundations of Distributed Systems first.

This course unlocks once you've finished its prerequisite. Open prerequisite →

Prerequisites

Foundations of Distributed Systems not yet

Complete prerequisites first to enroll.

reading · 30 min + ~231 min canonical

The Consensus Problem and Atomic Commit (2PC)

The last course ended on a hard truth: consensus — getting a set of nodes to agree on a single value — is impossible to guarantee in an asynchronous system with failures (FLP). Th…

primary MIT 6.5840 — Raft and Paxos lectures + Lab 2

preview →

reading · 35 min + ~231 min canonical L1

Raft: Consensus You Can Actually Understand

Consensus was, for decades, synonymous with Paxos — a correct but famously baffling algorithm that even experts struggle to explain, let alone implement correctly. Then in 2014, R…

primary MIT 6.5840 — Raft and Paxos lectures + Lab 2

after L1 locked

reading · 30 min + ~231 min canonical L1

State Machine Replication, Quorums, and Consistent Hashing

Raft gives you a consistent replicated log. This lesson is what you do with it — and how replication and partitioning actually build the fault-tolerant, scalable data systems you …

primary MIT 6.5840 — Raft and Paxos lectures + Lab 2

after L2 locked

reading · 30 min + ~231 min canonical L1

Consistency Models: Linearizability vs Serializability

"Consistency" is one of the most overloaded words in computing, and two of its meanings — linearizability and serializability — sound almost identical, are constantly confused (ev…

primary MIT 6.5840 — Raft and Paxos lectures + Lab 2

after L3 locked

reading · 35 min + ~231 min canonical L1

CRDTs and the Ruby Distributed-Systems Lens

This lesson closes the distributed-systems block with the technique that makes coordination-free collaboration possible, and then cashes the whole quarter into the tools you use. …

primary MIT 6.5840 — Raft and Paxos lectures + Lab 2

after L4 locked

exercise reading · 15 min L1

Exercises: Easy (Warm-up)

- [ ] Implement Two-Phase Commit (2PC) in Ruby — Coordinator + 2 participants, handle commit and abort - [ ] Diagram the Raft leader election process — Draw state transitions: fol…

after L5 locked

exercise reading · 30 min L1

Exercises: Medium (Core)

- [ ] MIT 6.5840 Lab 3A: Raft Leader Election — Implement leader election with randomized timeouts - [ ] MIT 6.5840 Lab 3B: Raft Log — Implement log replication, AppendEntries RPC…

after L6 locked

exercise reading · 45 min L1

Exercises: Hard (Stretch)

- [ ] MIT 6.5840 Lab 4A: KV Raft — Key/value service on top of Raft (without snapshots) - [ ] MIT 6.5840 Lab 4B: KV Raft with Snapshots — Add snapshot support for log compaction -…

after L7 locked

exercise reading · 60 min L1

Mini-Project

- [ ] Implement a simplified Raft in Ruby — Leader election, log replication, and commitment across 5 nodes; test with simulated network partitions and leader failures; visualize …

after L8 locked

L10

project reading · 360 min L1

Project: Two-Phase Commit in Ruby

Implement 2PC with a coordinator and 3 participants communicating via TCP sockets. Simulate participant crashes (random failures) and show how 2PC blocks. Then implement a timeout…

after L9 locked

L11

project reading · 300 min L1

Project: CRDT Collection in Ruby

Implement 4 CRDTs: G-Counter (grow-only counter), PN-Counter (increment/decrement), G-Set (grow-only set), and LWW-Register (last-writer-wins). Write property-based tests proving …

after L10 locked

L12

project reading · 240 min L1

Project: Consistent Hashing Ring

Build a consistent hashing ring in Ruby with virtual nodes. Support adding/removing servers, key lookup, and demonstrate minimal key redistribution when servers change. Visualize …

after L11 locked

L13

assessment reading · 63 min L1

Self-Assessment: Consensus and Replication

- [ ] What is the consensus problem? Why is it hard in distributed systems? - [ ] Explain Two-Phase Commit. What happens when the coordinator crashes? - [ ] Explain Raft consensus…

after L12 locked

L14

assessment reading · 60 min L1

Quarter 9 Gate Check: Distributed Systems

- [ ] Course 9.1 knowledge check passed - [ ] Course 9.2 knowledge check passed - [ ] Distributed KV Store with Raft capstone completed

after L13 locked

14 lessons. Read in order; spiral back when you need to. By the end you'll have used the core ideas twice — once on the abstract, once on something you'll meet at work next week.