Raft State Machine Safety Property

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。