func join(c *cli.Context) {
	dflag := getDiscovery(c)
	if dflag == "" {
		log.Fatalf("discovery required to join a cluster. See '%s join --help'.", c.App.Name)
	}

	addr := c.String("advertise")
	if addr == "" {
		log.Fatal("missing mandatory --advertise flag")
	}
	if !checkAddrFormat(addr) {
		log.Fatal("--advertise should be of the form ip:port or hostname:port")
	}

	joinDelay, err := time.ParseDuration(c.String("delay"))
	if err != nil {
		log.Fatalf("invalid --delay: %v", err)
	}
	if joinDelay < time.Duration(0)*time.Second {
		log.Fatalf("--delay should not be a negative number")
	}

	hb, err := time.ParseDuration(c.String("heartbeat"))
	if err != nil {
		log.Fatalf("invalid --heartbeat: %v", err)
	}
	if hb < 1*time.Second {
		log.Fatal("--heartbeat should be at least one second")
	}
	ttl, err := time.ParseDuration(c.String("ttl"))
	if err != nil {
		log.Fatalf("invalid --ttl: %v", err)
	}
	if ttl <= hb {
		log.Fatal("--ttl must be strictly superior to the heartbeat value")
	}

	d, err := discovery.New(dflag, hb, ttl, getDiscoveryOpt(c))
	if err != nil {
		log.Fatal(err)
	}

	// if joinDelay is 0, no delay will be executed
	// if joinDelay is larger than 0,
	// add a random delay between 0s and joinDelay at start to avoid synchronized registration
	if joinDelay > 0 {
		r := rand.New(rand.NewSource(time.Now().UTC().UnixNano()))
		delay := time.Duration(r.Int63n(int64(joinDelay)))
		log.Infof("Add a random delay %s to avoid synchronized registration", delay)
		time.Sleep(delay)
	}

	for {
		log.WithFields(log.Fields{"addr": addr, "discovery": dflag}).Infof("Registering on the discovery service every %s...", hb)
		if err := d.Register(addr); err != nil {
			log.Error(err)
		}
		time.Sleep(hb)
	}
}

func list(c *cli.Context) {
	dflag := getDiscovery(c)
	if dflag == "" {
		log.Fatalf("discovery required to list a cluster. See '%s list --help'.", c.App.Name)
	}
	timeout, err := time.ParseDuration(c.String("timeout"))
	if err != nil {
		log.Fatalf("invalid --timeout: %v", err)
	}

	d, err := discovery.New(dflag, timeout, 0, getDiscoveryOpt(c))
	if err != nil {
		log.Fatal(err)
	}

	ch, errCh := d.Watch(nil)
	select {
	case entries := <-ch:
		for _, entry := range entries {
			fmt.Println(entry)
		}
	case err := <-errCh:
		log.Fatal(err)
	case <-time.After(timeout):
		log.Fatal("Timed out")
	}
}

func parseDiscoveryOptions(backendAddress string, clusterOpts map[string]string) (time.Duration, discovery.Backend, error) {
	heartbeat, ttl, err := discoveryOpts(clusterOpts)
	if err != nil {
		return 0, nil, err
	}

	backend, err := discovery.New(backendAddress, heartbeat, ttl, clusterOpts)
	if err != nil {
		return 0, nil, err
	}
	return heartbeat, backend, nil
}

func startDiscovery(cfg *config.ClusterCfg) ([]config.Option, error) {
	if cfg == nil {
		return nil, fmt.Errorf("discovery requires a valid configuration")
	}

	hb := time.Duration(cfg.Heartbeat) * time.Second
	if hb == 0 {
		hb = defaultHeartbeat
	}
	logrus.Infof("discovery : %s $s", cfg.Discovery, hb.String())
	d, err := discovery.New(cfg.Discovery, hb, ttlFactor*hb)
	if err != nil {
		return nil, err
	}

	if cfg.Address == "" {
		iface, err := net.InterfaceByName("eth0")
		if err != nil {
			return nil, err
		}
		addrs, err := iface.Addrs()
		if err != nil || len(addrs) == 0 {
			return nil, err
		}
		ip, _, _ := net.ParseCIDR(addrs[0].String())
		cfg.Address = ip.String()
	}

	if ip := net.ParseIP(cfg.Address); ip == nil {
		return nil, errors.New("address config should be either ipv4 or ipv6 address")
	}

	if err := d.Register(cfg.Address + ":0"); err != nil {
		return nil, err
	}

	options := []config.Option{config.OptionDiscoveryWatcher(d), config.OptionDiscoveryAddress(cfg.Address)}
	go func() {
		for {
			select {
			case <-time.After(hb):
				if err := d.Register(cfg.Address + ":0"); err != nil {
					logrus.Warn(err)
				}
			}
		}
	}()
	return options, nil
}

// Initialize the discovery service.
func createDiscovery(uri string, c *cli.Context, discoveryOpt []string) discovery.Backend {
	hb, err := time.ParseDuration(c.String("heartbeat"))
	if err != nil {
		log.Fatalf("invalid --heartbeat: %v", err)
	}
	if hb < 1*time.Second {
		log.Fatal("--heartbeat should be at least one second")
	}

	// Set up discovery.
	discovery, err := discovery.New(uri, hb, 0, getDiscoveryOpt(c))
	if err != nil {
		log.Fatal(err)
	}

	return discovery
}

func TestNew(t *testing.T) {
	d, err := discovery.New("file:///path/to/file", 0, 0)
	assert.NoError(t, err)
	assert.Equal(t, d.(*Discovery).path, "/path/to/file")
}

func (s *DiscoverySuite) TestNew(c *check.C) {
	d, err := discovery.New("file:///path/to/file", 0, 0, nil)
	c.Assert(err, check.IsNil)
	c.Assert(d.(*Discovery).path, check.Equals, "/path/to/file")
}