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!

@lnattrass: I've swapped the fatal calls with errors, and swapped in the zap logging framework for structured logs I may replace the UDP transport with an authenticated transport at some stage - this maybe: xtaci/kcp-go

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 tomtaylor for the upstream work on this.

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