Use this skill when working on Raft replication, consensus state, or log/application ordering.
Core safety rules:
- Only the leader accepts writes; followers replicate and apply in order.
- Log matching property must hold; conflicting entries are overwritten.
- Commit index advances only when entries are replicated to a quorum.
Implementation guidance:
- Identify the Raft module boundaries and avoid mixing consensus logic with storage or API layers.
- Keep persistence of log/state separate from in-memory state machines.
- Ensure snapshot installation and log truncation are consistent with the applied index.
- Membership changes must follow the project’s chosen approach (joint consensus or staged transitions).
- When adding new commands, ensure they are deterministic and idempotent when applied.
Testing focus:
- Leader failover and re-election.
- Log divergence and recovery.
- Snapshot restore and state replay.
Pitfalls:
- Applying out-of-order entries.
- Committing entries without quorum.
- Mixing wall-clock time with term/index logic.