This repo is a minimalistic reproduction of Raft for educational purposes.
The classic Raft paper - https://raft.github.io/raft.pdf. It's probably one of the more readable papers I've come across. Pair this with the Raft visualisation which is a great tool to understand Raft.
Most of the code lives in the main.rs file currently, which is by design since this is an educational project. The only things I placed outside of the main.rs file were the clock module and the storage module. There is also a types.rs file for the more complicated types.
I separated out the storage layers and the clock layers because I was unsure what I was doing with it initially so I wanted to hide it behind an API and worry about the implementation later.
The clock injection itself wasn't a big deal actually but I ended up doing a plain-text CSV file with no indexing for storage which will probably be a pretty big problem at scale. This is still something I need to fix.
There are 3 main components to a Raft cluster
- Storage (represented in the storage module)
- Clocks (represented in the
clock.rsfile) - Networking (represented as the RPCManager struct in
main.rs) - Nodes or servers (represented as the RaftNode struct in
main.rs)
The node struct contains most of the logic around the RPC methods (shown in the screenshot below)
I've ended up creating a little bit of monstrosity in terms of testing because I ended up going with creating explicit scenarios. But, I've tried as far as I can to create a deterministic state machine that can be tested by mocking the networking layer and the clocks. This allows me to realiably forward time and drop messages between nodes to re-create real-world situation.
The testing logic is housed within the TestCluster struct in main.rs. The tests using this struct attempt to re-create explicit scenarios like a concurrent leader election and network partition to ensure the logic works correctly.
Currently the code is able to handle:
- Leader Election & Stability
- Log Replication
- Durable storage and recovery from storage
- Network partition recovery
What I have yet to do:
- Log snapshots
- Benchmarks
A huge part of accomplishing this was being able to reference existing repos that do a Raft implementation
- Phil Eaton's Raft implementation in Rust (https://github.com/eatonphil/raft-rs)
- Jacky Zhao's Raft implementation also in Rust (https://github.com/jackyzha0/miniraft)
- TLA+ spec of Raft (https://github.com/ongardie/raft.tla/tree/master)
A large part of the testing inspiration came from the second repo.