raft

States:

  • following – when node see leader
  • candidate – when node doesn’t see leader
  • leader

Raft formila (n / 2) – 1

Rules:

  • A Raft cluster of 3 nodes can tolerate a single node failure while a cluster of 5 can tolerate 2 node failures.
  • If any of the followers didn’t notice leader they try to become a leader
  • Candidate should request votes from other participants to become a leader
  • Leader update info when all nodes are in sync, after that leader acknowledge app which sent write request.
  • if 2 nodes become a leader, election start again
  • leader should send heartbeat interval, follower have heartbeat timeout, if timeout elapsed follower become candidate
  • during network partitions 2 leader can be exist, after healing second leader rollback all commits. The second leader with less nodes in partition

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