ideahitme / go-raft

Raft Consensus in Go

Go-raft

Simple implementation of the Raft Consensus Algorithm in Go. At this moment with the sole purpose of self-learning and exploration

Raft Consensus Algorithm

Raft consensus algorithm is an algorithm which allows to have a fault-tolerant replicated system (e.g. distributed hash table). It is a widely used algorithm, which is proven to be simple yet efficient.

The problems arises, when we have a set of machines (nodes), which should have a replicated state across the cluster. We have a client interacting with one of the machines (leader), and sending a request to either set or get a value.

The following is the high-level description of the algorithm followed by the list of resources used

State of a node

1. Follower - a slave node
2. Candidate - node ready to become a leader
3. Leader - current master of the cluster

Priniciples of work

Leader election

All nodes start in the follower state. There are two timeouts:

1. Election timeout - amount of time a follower waits until becoming a candidate. Each node gets a random value between 150ms to 300ms.
2. Heartbeat timeout - amount of time followers are waiting for pings from the leader. If timeout is exceeded, a node will strive to become a candidate.

After the election timeout a follower become a candidate and starts a new election term. To start a campaign a node must send the list of its last committed logs and the current term. If the voters find the last commit or the latest term to be unreliable they will reject the node. Otherwise they will vote for the node.

In case if two nodes get the same number of votes, the voting will be restarted automatically (on election timeout). Due to random length of the timeout collisions will stop occuring.

Log replication

Safety

References

1. https://www.usenix.org/conference/atc14/technical-sessions/presentation/ongaro
2. https://raft.github.io/raft.pdf
3. https://raft.github.io/
4. http://thesecretlivesofdata.com/raft/

License

MIT License

Copyright (c) 2016 Yerken (ideahitme)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.