Etcd is a distributed key-value store that provides a reliable way to store data across a cluster of machines. One of its key features is its consensus mechanism, which ensures that all nodes in the cluster agree on the state of the system.
Consensus Algorithm
Etcd uses the Raft consensus algorithm, which is a leader-based algorithm designed to ensure consistency in a distributed system. Raft divides the cluster into three roles: leader, follower, and candidate.
- Leader: The leader is responsible for managing the log entries and replicating them to the followers.
- Follower: Followers receive log entries from the leader and replicate them to their local storage.
- Candidate: Candidates are nodes that believe they should be the leader and start an election to become the leader.
Benefits of Raft
- High Availability: Raft ensures that the system remains available even if some nodes fail.
- Safety: Raft guarantees that the system will not diverge, meaning that all nodes will eventually agree on the same state.
- Fault Tolerance: Raft can handle a majority of node failures without losing data.
Example Usage
Suppose you want to store a configuration setting in etcd. You would first write the value to the leader node. The leader would then replicate the write operation to all followers, ensuring that all nodes agree on the new state.
curl -X PUT -d value="123" http://localhost:2379/v2/keys/config setting
Learn More
For more information about etcd and its consensus mechanism, please visit our documentation page: /etcd_documentation