I went with Redis-style async replication because I could actually defend it, and pivoted to Raft semantics when they pushed on consistency guarantees.
Start by clarifying requirements and scale, then walk through the core components: leader election (e.g., Raft or Redis Sentinel), log replication with quorum acknowledgment, and consistency guarantees. Use a concrete write example to show data flow from leader to follower, and explain how failover preserves durability and prevents split-brain. Finally, discuss read paths and trade-offs between consistency and latency.
Pro tip: Emphasize the importance of term numbers and commit indexes in Raft-like protocols to prevent split-brain and ensure linearizability; mention how Discord’s scale might influence choices like using a consensus layer for metadata vs. a simpler replication for high-throughput channels.
Ask about expected scale, consistency needs (strong vs. eventual), latency tolerance, and failure scenarios. This shapes whether you choose Raft, Paxos, or a Redis-style replication.
Describe a term-based election with randomized timeouts, quorum voting, and heartbeats for failure detection. Explain how a new leader is chosen and how old leaders step down.
Walk through the write path: leader appends to log, replicates to followers, commits after quorum acknowledgment, and applies to state machine. Discuss consistency models (linearizable writes, sequential reads) and how followers catch up via log matching.
Explain how quorum and term numbers prevent split-brain. Show a failover scenario: leader crashes, new leader elected, uncommitted entries handled, and clients redirected.
Discuss read options: linearizable reads via leader or quorum, stale reads from followers, and lease-based reads. Highlight trade-offs between consistency, latency, and availability.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.