RaftEx

⚠️ EXPERIMENTAL / UNDER ACTIVE DEVELOPMENT ⚠️

This library is an experimental Elixir port of the RabbitMQ RA Raft consensus algorithm. It is currently in early development and NOT READY FOR PRODUCTION USE.

Raft consensus algorithm implementation in Elixir, ported from the RabbitMQ RA library (original Erlang repo).

Overview

RaftEx implements the Raft consensus algorithm, providing:

• Leader Election: Pre-vote and candidate phases with quorum-based voting
• Log Replication: Write-ahead log (WAL) with batched writes and fsync support
• Snapshotting: Point-in-time state snapshots with chunked transfer
• Cluster Membership: Dynamic membership changes (join/leave)
• State Machine: Pluggable state machine interface for application logic
• Consistent Queries: Leader-verified reads with majority acknowledgement

Current Status

✅ Implemented

🚧 In Progress

❌ Not Started

Installation

⚠️ This package is not yet published to Hex.pm due to its experimental status.

If available, add to your mix.exs:

def deps do
  [
    {:raft_ex, "~> 0.0.2"}
  ]
end

Or use directly from Git:

def deps do
  [
    {:raft_ex, git: "https://github.com/your-org/raft_ex", branch: "main"}
  ]
end

Quick Start

# Start the RaftEx system
RaftEx.start_in("/tmp/raft_data")

# Define a simple state machine
defmodule CounterMachine do
  @behaviour RaftEx.Machine

  @impl RaftEx.Machine
  def init(_conf), do: 0

  @impl RaftEx.Machine
  def apply(_meta, {:increment}, state), do: {state + 1, state + 1}
  def apply(_meta, {:get}, state), do: {state, state}
end

# Start a cluster (single node for testing)
server_id = {:server1, node()}
machine = {:machine, CounterMachine, %{}}

{:ok, _} = RaftEx.start_cluster(
  :default,
  :my_cluster,
  machine,
  [server_id]
)

# Send a command
{:ok, reply, _leader} = RaftEx.process_command(server_id, {:increment})
IO.inspect(reply) # => 1

Architecture

┌─────────────────────────────────────────────────────────────┐
│                        RaftEx.Server                        │
│  ┌─────────────┐  ┌──────────────┐  ┌────────────────────┐ │
│  │   Leader    │  │  Follower    │  │    Candidate       │ │
│  │   State     │  │  State       │  │    State           │ │
│  └──────┬──────┘  └──────┬───────┘  └────────┬───────────┘ │
│         │                │                    │             │
│  ┌──────▼────────────────▼────────────────────▼───────────┐ │
│  │              Server Process (gen_statem)               │ │
│  └──────────────────────┬───────────────────────────────┘ │
│                         │                                 │
│  ┌──────────────────────▼───────────────────────────────┐ │
│  │                 RaftEx.Log                           │ │
│  │  ┌────────────┐  ┌────────────┐  ┌───────────────┐  │ │
│  │  │   WAL      │  │  Mem Table │  │   Snapshots   │  │ │
│  │  │ (GenServer)│  │   (ETS)    │  │   (Files)     │  │ │
│  │  └────────────┘  └────────────┘  └───────────────┘  │ │
│  └──────────────────────────────────────────────────────┘ │
│                         │                                 │
│  ┌──────────────────────▼───────────────────────────────┐ │
│  │              State Machine (Pluggable)                │ │
│  └──────────────────────────────────────────────────────┘ │
└─────────────────────────────────────────────────────────────┘

Key Components

• RaftEx: Main public API for cluster and server management
• RaftEx.ServerProc: gen_statem process managing server lifecycle
• RaftEx.Server: Core Raft protocol logic (state transitions, RPC handling)
• RaftEx.Log: Persistent replicated log with WAL + mem table
• RaftEx.LogWal: Write-ahead log GenServer with batched fsync
• RaftEx.LogMeta: DETS + ETS backed metadata store
• RaftEx.Machine: Behaviour for pluggable state machines
• RaftEx.Server.Election: Leader election with pre-vote support
• RaftEx.Server.RpcHandler: AppendEntries, InstallSnapshot, Heartbeat handlers

Configuration

# System configuration
%{
  name: :default,
  data_dir: "/var/lib/raft_ex",
  wal_max_size_bytes: 256_000_000,
  wal_max_batch_size: 8192,
  wal_sync_method: :datasync, # :fsync | :datasync | :none
  wal_compute_checksums: true,
  segment_max_entries: 4096,
  segment_max_size_bytes: 64_000_000
}

# Server configuration
%{
  id: {:server1, node()},
  uid: "unique_id",
  cluster_name: :my_cluster,
  initial_members: [{:server1, node()}, {:server2, node()}],
  machine: {:machine, MyMachine, %{}}
}

Development

# Install dependencies
mix deps.get

# Run tests
mix test

# Run tests with coverage
mix test --cover

# Check formatting
mix format --check-formatted

# Generate documentation
mix docs

Contributing

This project is in early development. Contributions are welcome but please note:

1. This is experimental software - expect breaking changes
2. All contributions must include tests
3. Follow the existing code style (mix format)
4. Document public APIs with @doc and @moduledoc

License

Dual-licensed under:

• Mozilla Public License 2.0 (MPL-2.0)
• Apache License 2.0 (Apache-2.0)

See LICENSE, LICENSE-APACHE2, and LICENSE-MPL-RabbitMQ for details.

Changelog

See CHANGELOG.md for a full list of changes.

Acknowledgments

• Original implementation: RabbitMQ RA
• Raft paper: In Search of an Understandable Consensus Algorithm