Handle RequestVote RPC - The Elector | Build Distributed Systems

      ARCHIVED from builddistributedsystem.com on 2026-04-28
      — URL: https://builddistributedsystem.com/tracks/elector/tasks/task-5-4-request-vote
    

                      TASK
                    

Implementation

Implement the RequestVote RPC. Candidates request votes from other nodes. Nodes grant their vote if the candidate's term is current and they have not already voted in this term.

Sample Test Cases

Grant vote to same term candidateTimeout: 5000ms

Input

{"src":"c0","dest":"n1","body":{"type":"init","msg_id":1,"node_id":"n1","node_ids":["n1","n2","n3"]}}
{"src":"c0","dest":"n1","body":{"type":"set_term","msg_id":2,"term":2}}
{"src":"n2","dest":"n1","body":{"type":"request_vote","msg_id":3,"term":2,"candidate_id":"n2","last_log_index":0,"last_log_term":0}}

Expected Output

{"src":"n1","dest":"c0","body":{"type":"init_ok","in_reply_to":1,"msg_id":0}}
{"src":"n1","dest":"c0","body":{"type":"set_term_ok","in_reply_to":2,"msg_id":1}}
{"src":"n1","dest":"n2","body":{"type":"request_vote_ok","in_reply_to":3,"msg_id":2,"term":2,"vote_granted":true}}

Hints

Hint 1▾

Grant vote if candidate term >= current term

Hint 2▾

Only vote once per term

Hint 3▾

Update term if candidate has higher term

Resources

Raft Lecture

MIT 6.824 Raft lecture by Robert Morris

                      OVERVIEW
                    

Theoretical Hub

Vote Granting

A node grants its vote if: the candidate term is at least as recent as its own, and it has not voted for another candidate in this term. This ensures at most one leader per term.

Key Concepts

votingterm comparisonvote granting

main.py

python

Handle RequestVote RPC - The Elector | Build Distributed Systems