raft-protocol-implementation

Raft protocol implementation as part of "Distributed databases" course in UCU

Raft decomposes the consensus problem into three relatively independent subproblems:

• Leader election: a new leader must be chosen when an existing leader fails.
• Log replication: the leader must accept log entries
• Safety: the key safety property for Raft is the State Machine Safety Property. If any server has applied a particular log entry to its state machine, then no other server may apply a different command for the same log index. The solution involves an additional restriction on the election mechanism.

Raft guarantees that each of these properties is true at all times.

• Election Safety: at most one leader can be elected in a given term.
• Leader Append-Only: a leader never overwrites or deletes entries in its log; it only appends new entries.
• Log Matching: if two logs contain an entry with the same index and term, then the logs are identical in all entries up through the given index.
• Leader Completeness: if a log entry is committed in a given term, then that entry will be present in the logs of the leaders for all higher-numbered terms.
• State Machine Safety: if a server has applied a log entry at a given index to its state machine, no other server will ever apply a different log entry for the same index.

Curl

curl -L -d '{"action":"Create", "data":{"x": "123"}}' -H "Content-Type: application/json" -X POST http://localhost:8080/append