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moby--moby/daemon/discovery.go

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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) (discovery.Backend, error) {
var (
discoveryBackend discovery.Backend
err error
)
if discoveryBackend, err = discovery.New(backend, defaultDiscoveryHeartbeat, defaultDiscoveryTTL); 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)
}
}