package daemon
 
 import (
 	"time"
 
 	log "github.com/Sirupsen/logrus"
 	"github.com/docker/docker/pkg/discovery"
 
 	// Register the libkv backends for discovery.
 	_ "github.com/docker/docker/pkg/discovery/kv"
 )
 
 const (
 	// defaultDiscoveryHeartbeat is the default value for discovery heartbeat interval.
 	defaultDiscoveryHeartbeat = 20 * time.Second
 
 	// defaultDiscoveryTTL is the default TTL interface for discovery.
 	defaultDiscoveryTTL = 60 * time.Second
 )
 
 // initDiscovery initialized the nodes discovery subsystem by connecting to the specified backend
 // and start a registration loop to advertise the current node under the specified address.

 func initDiscovery(backend, address string, clusterOpts map[string]string) (discovery.Backend, error) {

 	var (
 		discoveryBackend discovery.Backend
 		err              error
 	)

 	if discoveryBackend, err = discovery.New(backend, defaultDiscoveryHeartbeat, defaultDiscoveryTTL, clusterOpts); err != nil {

 		return nil, err
 	}
 
 	// We call Register() on the discovery backend in a loop for the whole lifetime of the daemon,
 	// but we never actually Watch() for nodes appearing and disappearing for the moment.
 	go registrationLoop(discoveryBackend, address)
 	return discoveryBackend, nil
 }
 
 // registrationLoop registers the current node against the discovery backend using the specified
 // address. The function never returns, as registration against the backend comes with a TTL and
 // requires regular heartbeats.
 func registrationLoop(discoveryBackend discovery.Backend, address string) {
 	for {
 		if err := discoveryBackend.Register(address); err != nil {
 			log.Errorf("Registering as %q in discovery failed: %v", address, err)
 		}
 		time.Sleep(defaultDiscoveryHeartbeat)
 	}
 }