package cluster import ( "context" "github.com/cenk/backoff" "github.com/containous/traefik/log" "github.com/containous/traefik/safe" "github.com/containous/traefik/types" "github.com/docker/leadership" "time" ) // Leadership allows leadership election using a KV store type Leadership struct { *safe.Pool *types.Cluster candidate *leadership.Candidate leader safe.Safe listeners []LeaderListener } // NewLeadership creates a leadership func NewLeadership(ctx context.Context, cluster *types.Cluster) *Leadership { return &Leadership{ Pool: safe.NewPool(ctx), Cluster: cluster, candidate: leadership.NewCandidate(cluster.Store, cluster.Store.Prefix+"/leader", cluster.Node, 20*time.Second), listeners: []LeaderListener{}, } } // LeaderListener is called when leadership has changed type LeaderListener func(elected bool) error // Participate tries to be a leader func (l *Leadership) Participate(pool *safe.Pool) { pool.GoCtx(func(ctx context.Context) { log.Debugf("Node %s running for election", l.Cluster.Node) defer log.Debugf("Node %s no more running for election", l.Cluster.Node) backOff := backoff.NewExponentialBackOff() operation := func() error { return l.run(ctx, l.candidate) } notify := func(err error, time time.Duration) { log.Errorf("Leadership election error %+v, retrying in %s", err, time) } err := backoff.RetryNotify(operation, backOff, notify) if err != nil { log.Errorf("Cannot elect leadership %+v", err) } }) } // AddListener adds a leadership listerner func (l *Leadership) AddListener(listener LeaderListener) { l.listeners = append(l.listeners, listener) } // Resign resigns from being a leader func (l *Leadership) Resign() { l.candidate.Resign() log.Infof("Node %s resigned", l.Cluster.Node) } func (l *Leadership) run(ctx context.Context, candidate *leadership.Candidate) error { electedCh, errCh := candidate.RunForElection() for { select { case elected := <-electedCh: l.onElection(elected) case err := <-errCh: return err case <-ctx.Done(): l.candidate.Resign() return nil } } } func (l *Leadership) onElection(elected bool) { if elected { log.Infof("Node %s elected leader ♚", l.Cluster.Node) l.leader.Set(true) l.Start() } else { log.Infof("Node %s elected slave ♝", l.Cluster.Node) l.leader.Set(false) l.Stop() } for _, listener := range l.listeners { err := listener(elected) if err != nil { log.Errorf("Error calling Leadership listener: %s", err) } } } // IsLeader returns true if current node is leader func (l *Leadership) IsLeader() bool { return l.leader.Get().(bool) }