C-Raft

C-Raft is a fully asynchronous C implementation of the Raft consensus protocol.

Design

The library has modular design: its core part implements only the core Raft algorithm logic, in a fully platform independent way. On top of that, a pluggable interface defines the I/O implementation for networking and disk persistence.

A stock implementation of the I/O interface is provided when building the library with default options. It is based on libuv and should fit the vast majority of use cases.

Features

C-Raft implements all the basic features described in the Raft dissertation:

  • Leader election

  • Log replication

  • Log compaction

  • Membership changes

It also includes a few optional enhancements:

  • Optimistic pipelining to reduce log replication latency

  • Writing to leader’s disk in parallel

  • Automatic stepping down when the leader loses quorum

  • Leadership transfer extension

  • Non-voting servers

Quick start

Make sure that libuv is installed on your system, then run:

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autoreconf -i
./configure --enable-example
make

Then create a main.c file with this simple test program that just runs a single raft server and implements a basic state machine for incrementing a counter:

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#include <raft.h>
#include <raft/uv.h>

static raft_id id = 12345;
static const char *address = "127.0.0.1:8080";
static const char *dir = "/tmp/raft-quick-start";
static struct uv_loop_s loop;
static struct raft_uv_transport transport;
static struct raft_io io;
static struct raft_fsm fsm;
static struct raft raft;
static struct raft_configuration conf;
static struct uv_timer_s timer;
static struct raft_apply apply;
static unsigned counter = 0;
static uint64_t command;

static int applyCommand(struct raft_fsm *fsm,
                        const struct raft_buffer *buf,
                        void **result) {
    counter += *(uint64_t *)buf->base;
    printf("counter: %u\n", counter);
    return 0;
}

static void submitCommand(uv_timer_t *timer) {
    struct raft_buffer buf;
    command = uv_now(timer->loop) % 10;
    buf.len = sizeof command;
    buf.base = &command;
    raft_apply(&raft, &apply, &buf, 1, NULL);
}

int main() {
    mkdir(dir, 0755);
    uv_loop_init(&loop);
    raft_uv_tcp_init(&transport, &loop);
    raft_uv_init(&io, &loop, dir, &transport);
    fsm.apply = applyCommand;
    raft_init(&raft, &io, &fsm, id, address);
    raft_configuration_init(&conf);
    raft_configuration_add(&conf, id, address, RAFT_VOTER);
    raft_bootstrap(&raft, &conf);
    raft_start(&raft);
    uv_timer_init(&loop, &timer);
    uv_timer_start(&timer, submitCommand, 0, 1000);
    uv_run(&loop, UV_RUN_DEFAULT);
}

You can compile and run it with:

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cc main.c -o main -lraft -luv && ./main

Licence

This raft C library is released under a slightly modified version of LGPLv3, that includes a copiright exception letting users to statically link the library code in their project and release the final work under their own terms. See the full license text.