election

ETCD Leader Election

Use etcd for leader election if you have several instances of a service running in production and you only want one of the service instances to preform a task.

LeaderElection starts a goroutine which performs an election and maintains a leader while services join and leave the election. Calling Stop() will Concede() leadership if we currently have it.

import (
    "github.com/mailgun/holster"
    "github.com/mailgun/holster/election"
)

var wg holster.WaitGroup

// Start the goroutine and preform the election
leader, _ := election.New(election.Config{
    Endpoints:     []string{"http://192.168.99.100:2379"},
    Name: "my-service"
})

// Handle graceful shutdown
signalChan := make(chan os.Signal, 1)
signal.Notify(signalChan, os.Interrupt, os.Kill)

// Do periodic thing
tick := time.NewTicker(time.Second * 2)
wg.Loop(func() bool {
    select {
    case <-tick.C:
        // Are we currently leader?
        if leader.IsLeader() {
            err := DoThing()
            if err != nil {
                // Have another instance DoThing(), we can't for some reason
                leader.Concede()
            }
        }
        return true
    case <-signalChan:
        leader.Stop()
        return false
    }
})
wg.Wait()