refactor connection establishment

docker.go

@@ -6,6 +6,10 @@ import (
 	"strings"
 
 	"docker.io/go-docker/api/types"
+	"docker.io/go-docker/api/types/events"
+	"docker.io/go-docker/api/types/filters"
+	"github.com/cenkalti/backoff"
+	log "github.com/sirupsen/logrus"
 )
 
 type ipsToNamesMap map[string][]string
@@ -13,6 +17,8 @@ type ipsToNamesMap map[string][]string
 type dockerClienter interface {
 	ContainerList(context.Context, types.ContainerListOptions) ([]types.Container, error)
 	ContainerInspect(context.Context, string) (types.ContainerJSON, error)
+	Events(context.Context, types.EventsOptions) (<-chan events.Message, <-chan error)
+	Ping(context.Context) (types.Ping, error)
 }
 
 func getAllIPsToNames(client dockerClienter) (ipsToNamesMap, error) {
@@ -73,3 +79,60 @@ func getIPsToNames(client dockerClienter, id string) (ipsToNamesMap, error) {
 
 	return ipsToNames, nil
 }
+
+func listenForEvents(client dockerClienter) {
+	eventOpts := types.EventsOptions{
+		Filters: filters.NewArgs(
+			filters.Arg("type", "container"),
+			filters.Arg("event", "start"),
+			filters.Arg("event", "die"),
+		),
+	}
+
+	events, errors := client.Events(context.Background(), eventOpts)
+loop:
+	for {
+		select {
+		case event := <-events:
+			switch event.Action {
+			case "start":
+				ipsToNames, err := getIPsToNames(client, event.Actor.Attributes["name"])
+				if err != nil {
+					log.WithFields(
+						log.Fields{"container": event.Actor.ID},
+					).Errorf("could not get info for container: %s", err)
+					continue
+				}
+				err = addToEtcHosts(ipsToNames)
+				if err != nil {
+					log.WithFields(
+						log.Fields{"container": event.Actor.ID},
+					).Errorf("could not add container to hosts file: %s", err)
+				}
+			case "die":
+				// We remove by name because we cannot get the container's IP after it has been stopped.
+				// Names are supposed to be kept unique by the docker deamon.
+				removeFromEtcHosts(event.Actor.Attributes["name"])
+			}
+		case err := <-errors:
+			log.Errorf("error fetching event: %s", err)
+			break loop
+		}
+	}
+}
+
+func waitForConnection(client dockerClienter) {
+	err := backoff.Retry(func() error {
+		log.Info("retrying connection to docker")
+		_, err := client.Ping(context.Background())
+		if err != nil {
+			return fmt.Errorf("error pinging docker server: %s", err)
+		}
+		return nil
+	}, backoff.NewExponentialBackOff())
+	if err != nil {
+		// we should not get here with infinite backoff
+		log.Fatal(err)
+	}
+	log.Info("connected to docker daemon")
+}