MultiBully is a Go library for distributed leadership election on a UDP multicast enabled network, like a LAN. It uses the Bully algorithm, a relatively simply mechanism which may not be suitable for a large numbers of nodes.

I think there are some bugs and inefficiencies in my implementation of it. It always manages to converge on the correct leader, but it sometimes takes a few goes round. Please feel free to help!

The Bully algorithm elects the node with the largest pid to be leader. The pid doesn't necessarily need to be the process ID in the operating system – you could choose for this to be a timestamp or a fixed integer for each node. In this implementation, the combination of pid and IP address must be unique, so you can run multiple instances on a single host.

While MultiBully uses multicast UDP for communication between nodes, it transmits the non-multicast IP of each node in the communication packet, so you can point the follower at the new leader.

package main

import (
	"github.com/tomtaylor/multibully"
	"log"
	"os"
	"net"
)

func main() {
	address := "224.0.0.0:9999"
	iface := "en0"
	stop := make(chan struct{})
	pid := uint64(os.Getpid())

	p, err := multibully.NewParticipant(address, iface, pid, func(state int, ip *net.IP) {
		switch state {
		case multibully.Follower:
			log.Println("* Became Follower of", ip)
		case multibully.Leader:
			log.Println("* Became Leader")
		}
	})

	if err != nil {
		log.Fatal(err)
	}

	go p.StartElection()
	p.RunLoop(stop)
}

Thanks to oaStuff for their sample code which helped me understand how to implement the Bully algorithm.