Add: Build your own Raft (Java)

[naman1gupta]

Adds one entry to Build your own Distributed Systems, which currently has a single item and no consensus implementation in any language.

• Java: Build your own Raft: leader election, log replication, and the §5.4 safety rules

Why it fits the list:

• Built from the paper, not on a library. Plain Java 21, one runtime dependency (slf4j-api, for two debug lines). No etcd/jraft/Atomix doing the consensus.
• Follows the paper section by section, and the README maps each mechanism to its section: terms and roles (§5.1), randomised election timeouts and RequestVote (§5.2), AppendEntries with nextIndex/matchIndex backtracking (§5.3), the up-to-date-log vote restriction (§5.4.1), and current-term-majority commit (§5.4.2).
• Learnable by breaking it. The transport is a seam you can partition, delay and drop from a test. The headline test splits five nodes 3∥2, asserts the majority keeps committing while the minority commits nothing, heals, then asserts every node converges.
• Scope is stated honestly. The README has a "what is deliberately not implemented" section — no log compaction, no membership changes, no linearizable reads, no pre-vote — so a reader knows where the implementation stops.
• There is a live version to play with first: https://namangupta.me/raft-lab runs five nodes server-side and lets you kill the leader, partition the network and inject latency or loss from the browser, which is a gentler entry point than reading code cold.
• MIT licensed, 9 passing tests, and the README code sample is itself a test so the docs cannot drift from the API.

Happy to reshape the entry text or move it if you would rather it sat elsewhere.