Raft protocol

The Raft protocol is a consensus algorithm for maintaining a replicated log. It is designed to be easy to understand and implement, and it is based on a relatively simple model of a distributed system. The key idea behind Raft is to ensure that a single leader is responsible for making decisions about the state of the system, and all other nodes in the system follow the leader.

Raft defines three key components:

Leader: The leader is responsible for receiving client requests and forwarding them to the appropriate node in the cluster. It also manages the replication of the log to other nodes in the cluster.
Follower: Followers are responsible for replicating the log, and they vote on the leader election.
Candidate: Candidates are nodes that want to become the leader. They initiate an election by sending out RequestVote messages to all other nodes in the cluster.

Raft works as follows:

Initially, all nodes start as followers.
The leader is elected by a majority of nodes through an election process.
Once elected, the leader starts to receive client requests and replicates the log to the followers.
If the leader fails or becomes unresponsive, the followers will start a new election to elect a new leader.

Here's an example of a simple Raft cluster with 4 nodes:

In this example, Node 1 is the leader, and Nodes 2, 3 and 4 are followers.

If the leader Node 1 fails, a new leader is elected through the following process:

In this example, Node 2 is elected as the new leader, and Nodes 3 and 4 become followers again.

It's important to note that this is a very simplified example and in practice a Raft cluster will have many more nodes and a more complex communication pattern.