Added -dev flag

This commit adds the `-dev` flag to Relay's CLI. Setting it tells Relay
to run in development mode where it trades speed for developer
productivity.

Currently setting `-dev` will cause Relay to pull and re-pull Docker
images before running commands packaged as Docker images. This should
reduce the overhead of iterating on commands during development and
simplify command developers' workflows.

Fixes #950

Author: Kevin Smith

main.go

@@ -22,7 +22,8 @@ const (
 
 var configFile = flag.String("file", "", "Path to configuration file")
 var cpuprofile = flag.String("cpuprofile", "", "Write CPU profile to file")
-var memprofile = flag.String("memprofile", "", "write memory profile to this file")
+var memprofile = flag.String("memprofile", "", "Write memory profile to this file")
+var devMode    = flag.Bool("dev", false, "Enable developer mode")
 
 // Populated by build script
 var buildstamp string
@@ -139,6 +140,7 @@ func prepare() *config.Config {
 		os.Exit(BAD_CONFIG)
 		return nil
 	}
+	relayConfig.DevMode = *devMode
 	configureLogger(relayConfig)
 	return relayConfig
 }
@@ -169,7 +171,9 @@ func main() {
 		return
 	}
 	log.Infof("Relay %s is initializing.", relayConfig.ID)
-
+	if relayConfig.DevMode == true {
+		log.Warn("Developer mode enabled.")
+	}
 	myRelay, err := relay.NewRelay(relayConfig)
 	if err != nil {
 		log.Error(err)

relay/config/config.go

@@ -46,6 +46,7 @@ type Config struct {
 	Cog                   *CogInfo `yaml:"cog" valid:"required"`
 	EnginesEnabled        string   `yaml:"enabled_engines" env:"RELAY_ENABLED_ENGINES" valid:"exec_engines" default:"docker,native"`
 	ParsedEnginesEnabled  []string
+	DevMode               bool
 	Docker                *DockerInfo    `yaml:"docker" valid:"-"`
 	Execution             *ExecutionInfo `yaml:"execution" valid:"-"`
 }

relay/engines/docker.go

@@ -229,7 +229,31 @@ func (de *DockerEngine) attemptAuth() error {
 	return nil
 }
 
+func (de *DockerEngine) developerModeRefresh(bundle *config.Bundle) error {
+	if de.relayConfig.DevMode == true {
+		fullName := fmt.Sprintf("%s:%s", bundle.Docker.Image, bundle.Docker.Tag)
+		log.Warnf("Developer mode: Refreshing Docker image %s.", fullName)
+		err := de.pullImage(fullName)
+		if err != nil {
+			log.Errorf("Developer mode: Refresh of Docker image %s failed: %s.", fullName, err)
+			return err
+		}
+		image, _, err := de.client.ImageInspectWithRaw(context.Background(), fullName, false)
+		if err != nil {
+			log.Errorf("Developer mode: Docker image %s downloaded but can't be found locally: %s.", fullName, err)
+			return err
+		}
+		log.Warnf("Developer mode: Docker image %s refreshed. Image id is %s.", fullName, shortImageID(image.ID))
+	}
+	return nil
+}
+
 func (de *DockerEngine) newEnvironment(bundle *config.Bundle) (circuit.Environment, error) {
+	// Only happens if Relay is running in developer mode
+	err := de.developerModeRefresh(bundle)
+	if err != nil {
+		return nil, err
+	}
 	client, err := newClient(de.config)
 	if err != nil {
 		return nil, err
@@ -260,6 +284,10 @@ func (de *DockerEngine) needsUpdate(name, meta string) bool {
 }
 
 func (de *DockerEngine) pullImage(fullName string) error {
+	err := de.ensureConnected()
+	if err != nil {
+		return err
+	}
 	closer, pullErr := de.client.ImagePull(context.Background(), fullName,
 		types.ImagePullOptions{
 			All:          false,