Raft Server
A fault-tolerant key-value storage server built on a distributed network using the Raft consensus algorithm
What is Raft?
Raft is a consensus algorithm designed to be easily understandable while providing the same guarantees as Paxos. It allows a cluster of servers to agree on a shared state even in the presence of failures, ensuring that the system continues to operate correctly as long as a majority of servers remain functional.
The algorithm solves the fundamental problem of distributed systems: how do you get multiple servers to agree on the same sequence of operations when any of them might crash, network messages might be lost or delayed, and clocks aren't synchronized?
Key Features
This implementation provides a fault-tolerant key-value storage system with the following capabilities:
- Leader Election: Automatically elects a leader to coordinate operations across the cluster
- Log Replication: Ensures all servers maintain identical replicated logs of client operations
- Fault Tolerance: Continues operating correctly even when minority of servers fail
- Consistency Guarantees: Provides linearizable semantics for all read and write operations
- Automatic Recovery: Failed servers can rejoin the cluster and catch up on missed operations
How It Works
The Raft algorithm divides the consensus problem into three relatively independent subproblems:
Leader Election
A new leader must be chosen when an existing leader fails. Servers start as followers and transition to candidates when they don't hear from a leader. Candidates request votes from other servers, and a server becomes leader when it receives votes from a majority of the cluster.
Log Replication
The leader accepts client requests, appends them to its log, and replicates the log entries to follower servers. Once an entry is replicated on a majority of servers, it's considered committed and can be applied to the state machine.
Safety
Raft ensures that if any server has applied a particular log entry to its state machine, no other server can apply a different command for the same log index. This is achieved through election restrictions and commitment rules.