Raft: A Consensus Algorithm for Distributed Systems
A creative look at how Raft ensures that all nodes in a distributed system agree on the same state of the world.
In distributed systems, all nodes must agree on the same state of the world. This is because if nodes disagree, it can lead to problems such as data corruption and inconsistency.
Many different consensus algorithms can be used to ensure that all nodes in a distributed system agree on the same state of the world. One of the most popular consensus algorithms is Raft.
Raft Overview
Raft is a consensus algorithm designed to be simple, efficient, and fault-tolerant. It is based on a leader-based system, where one node is elected as the leader. The leader is responsible for proposing changes to the state of the world, and the other nodes in the system are responsible for voting on those changes.
The Raft Election Process
The Raft election process is triggered when the current leader fails or becomes unavailable. When this happens, the other nodes in the system start an election to elect a new leader.
The election process is based on a voting system—each node in the system votes for the node it believes should be the new leader. The node with the most votes becomes the new leader.
The Raft Log
Raft uses a log to keep track of the state of the world. The record is a sequence of entries, and each entry represents a change to the state of the world.
When the leader proposes a change to the state of the world, it appends the change to the log. The other nodes in the system then replicate the transition to their records.
The Raft Consensus Process
Once a change has been proposed and appended to the log, the Raft consensus process ensures that all nodes agree on the change.
The Raft consensus process is based on a heartbeat system. The leader sends heartbeats to the other nodes in the system. If a node does not receive a heartbeat from the leader within a certain period, it assumes that the leader is no longer available and starts an election.
The Raft Safety Rules
Raft is a safe consensus algorithm. This means that it is guaranteed to reach a consensus, even if some of the nodes in the system fail or become unavailable.
Raft achieves safety by following three rules:
- Leader Election Rule: There can only be one leader at a time.
- Log Replication Rule: All nodes in the system must have the same log.
- Safety Rule: Once a change has been committed to the record, it will never be rolled back.
The Raft Conclusion
Raft is a simple, efficient, and fault-tolerant consensus algorithm. It is a good choice for distributed systems that must ensure that all nodes agree on the same state of the world.