raftz

Implementation of the Raft consensus algorithm in Zig

Features

• Leader Election - Automatic leader election with randomized timeouts for split-vote prevention
• Log Replication - Reliable log replication across cluster nodes with consistency guarantees
• Persistence - Durable state storage with snapshot support for efficient recovery
• Pluggable State Machines - Bring your own state machine or use the built-in key-value store
• Network Transport - TCP-based RPC communication between cluster nodes
• Pre-vote Optimization - Reduces election disruptions from partitioned nodes
• ReadIndex Protocol - Linearizable reads with heartbeat confirmation and follower caching
• Leadership Transfer - Graceful leader handoff for maintenance and load balancing
• Dynamic Membership - Add/remove servers from a running cluster
• Non-voting Members (Learners) - Add learners that replicate logs but don't vote
• Client Session Tracking - Request deduping with cached responses for idempotent operations

Quick Start

Installation

zig fetch --save https://github.com/burdzwastaken/raftz/archive/refs/tags/v0.0.3.tar.gz

Basic Usage

const raft = @import("raftz");

// initialize state machine (built in k/v store)
var kv = raft.KvStore.init(allocator);
defer kv.deinit();

// configure cluster
const servers = [_]raft.ServerId{ 1, 2, 3 };
const cluster = raft.ClusterConfig.simple(&servers);

// create node with persistence
var storage = try raft.Storage.init(allocator, "data_dir");
defer storage.deinit();

var node = try raft.Node.init(
    allocator,
    .{ .id = 1 },
    cluster,
    kv.stateMachine(),
    &storage,
);
defer node.deinit();

// setup network transport
var transport = raft.Transport.init(allocator, 1000);
defer transport.deinit();

try transport.listen(.{ .host = "127.0.0.1", .port = 5001 });
try transport.addPeer(2, .{ .host = "127.0.0.1", .port = 5002 });

// start server
var server = raft.Server.init(allocator, &node, &transport);
try server.start();
defer server.stop();

Development

# dev shell
nix develop

# build
zig build

# tests
zig build test

# fmt
zig fmt --check src/ examples/

Examples

# simple node & RPC mocks
zig build run-simple

# client with log replication
zig build run-client

# full cluster with leader election and failover
zig build run-cluster

TODO

Zig Improvements

• Migrate to new Zig reader/writer I/O interfaces
• Optimize allocations and memory usage as we haven't focused on perf at all

Raft Enhancements

• Request batching/pipelining
  • Batch multiple client requests into single AppendEntries RPC
  • Pipeline multiple outstanding requests
  • Adaptive batching based on load
• Enhanced membership changes
  • Catch-up mechanism (snapshot transfer for new servers far behind)
  • Configuration change timeout/abort mechanism
  • Pre-replication before adding to old,new

Advanced Membership Features

• Non-voting members (learners)
  • Automatic promotion when caught up
• Witness members
  • Witness server type (votes but doesn't store log/snapshot)
  • AddWitness/RemoveWitness RPCs
  • Witness state sync

Credits

Thanks to Diego Ongaro and John Ousterhout for the excellent resources at https://raft.github.io/. Also a shout out to the many Raft implementations in the wild for inspiration!

License

MIT