Leader Election & Idempotency

Why you need a leader

Some decisions (who accepts writes, who assigns work) need exactly one node in charge at a time. Leader election lets a cluster agree on that node and detect when it needs replacing.

Raft, briefly

Raft is a consensus algorithm where nodes vote for a leader using randomized timeouts; the candidate with the most votes wins a term. The leader replicates a log to followers, and an entry is only considered committed once a majority has it — this survives any minority of node failures.

Idempotency saves you

A network timeout doesn't tell you if the request landed. If retries and duplicate delivery are inevitable, make operations idempotent: a client-generated idempotency key lets the server recognize and safely ignore a repeat of the same logical request.

Quick check: In Raft, when is a log entry considered committed?

• As soon as the leader writes it
• Once a majority of nodes have replicated it
• Once every node has replicated it