Disassociate instance id from application

This moves the instance id out of the app so that it is associated with an
instantiation of the runtime. The instance id is stored on the background
context. This allows allow contexts using the main background context to
include an instance id for log messages. It also simplifies the application
slightly.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

cmd/registry/main.go

@@ -15,7 +15,7 @@ import (
 	"github.com/Sirupsen/logrus/formatters/logstash"
 	"github.com/bugsnag/bugsnag-go"
 	"github.com/docker/distribution/configuration"
-	ctxu "github.com/docker/distribution/context"
+	"github.com/docker/distribution/context"
 	_ "github.com/docker/distribution/health"
 	_ "github.com/docker/distribution/registry/auth/silly"
 	_ "github.com/docker/distribution/registry/auth/token"
@@ -28,7 +28,6 @@ import (
 	"github.com/docker/distribution/version"
 	gorhandlers "github.com/gorilla/handlers"
 	"github.com/yvasiyarov/gorelic"
-	"golang.org/x/net/context"
 )
 
 var showVersion bool
@@ -67,9 +66,9 @@ func main() {
 	}
 
 	if config.HTTP.TLS.Certificate == "" {
-		ctxu.GetLogger(app).Infof("listening on %v", config.HTTP.Addr)
+		context.GetLogger(app).Infof("listening on %v", config.HTTP.Addr)
 		if err := http.ListenAndServe(config.HTTP.Addr, handler); err != nil {
-			ctxu.GetLogger(app).Fatalln(err)
+			context.GetLogger(app).Fatalln(err)
 		}
 	} else {
 		tlsConf := &tls.Config{
@@ -82,23 +81,23 @@ func main() {
 			for _, ca := range config.HTTP.TLS.ClientCAs {
 				caPem, err := ioutil.ReadFile(ca)
 				if err != nil {
-					ctxu.GetLogger(app).Fatalln(err)
+					context.GetLogger(app).Fatalln(err)
 				}
 
 				if ok := pool.AppendCertsFromPEM(caPem); !ok {
-					ctxu.GetLogger(app).Fatalln(fmt.Errorf("Could not add CA to pool"))
+					context.GetLogger(app).Fatalln(fmt.Errorf("Could not add CA to pool"))
 				}
 			}
 
 			for _, subj := range pool.Subjects() {
-				ctxu.GetLogger(app).Debugf("CA Subject: %s", string(subj))
+				context.GetLogger(app).Debugf("CA Subject: %s", string(subj))
 			}
 
 			tlsConf.ClientAuth = tls.RequireAndVerifyClientCert
 			tlsConf.ClientCAs = pool
 		}
 
-		ctxu.GetLogger(app).Infof("listening on %v, tls", config.HTTP.Addr)
+		context.GetLogger(app).Infof("listening on %v, tls", config.HTTP.Addr)
 		server := &http.Server{
 			Addr:      config.HTTP.Addr,
 			Handler:   handler,
@@ -106,7 +105,7 @@ func main() {
 		}
 
 		if err := server.ListenAndServeTLS(config.HTTP.TLS.Certificate, config.HTTP.TLS.Key); err != nil {
-			ctxu.GetLogger(app).Fatalln(err)
+			context.GetLogger(app).Fatalln(err)
 		}
 	}
 }
@@ -190,7 +189,7 @@ func configureLogging(ctx context.Context, config *configuration.Configuration)
 	if config.Log.Level == "" && config.Log.Formatter == "" {
 		// If no config for logging is set, fallback to deprecated "Loglevel".
 		log.SetLevel(logLevel(config.Loglevel))
-		ctx = ctxu.WithLogger(ctx, ctxu.GetLogger(ctx, "version"))
+		ctx = context.WithLogger(ctx, context.GetLogger(ctx, "version"))
 		return ctx, nil
 	}
 
@@ -224,8 +223,8 @@ func configureLogging(ctx context.Context, config *configuration.Configuration)
 			fields = append(fields, k)
 		}
 
-		ctx = ctxu.WithValues(ctx, config.Log.Fields)
-		ctx = ctxu.WithLogger(ctx, ctxu.GetLogger(ctx, fields...))
+		ctx = context.WithValues(ctx, config.Log.Fields)
+		ctx = context.WithLogger(ctx, context.GetLogger(ctx, fields...))
 	}
 
 	return ctx, nil

context/context.go

@@ -1,6 +1,7 @@
 package context
 
 import (
+	"code.google.com/p/go-uuid/uuid"
 	"golang.org/x/net/context"
 )
 
@@ -9,9 +10,31 @@ type Context interface {
 	context.Context
 }
 
-// Background returns a non-nil, empty Context.
+// instanceContext is a context that provides only an instance id. It is
+// provided as the main background context.
+type instanceContext struct {
+	Context
+	id string // id of context, logged as "instance.id"
+}
+
+func (ic *instanceContext) Value(key interface{}) interface{} {
+	if key == "instance.id" {
+		return ic.id
+	}
+
+	return ic.Context.Value(key)
+}
+
+var background = &instanceContext{
+	Context: context.Background(),
+	id:      uuid.New(),
+}
+
+// Background returns a non-nil, empty Context. The background context
+// provides a single key, "instance.id" that is globally unique to the
+// process.
 func Background() Context {
-	return context.Background()
+	return background
 }
 
 // WithValue returns a copy of parent in which the value associated with key is

registry/handlers/app.go

@@ -8,7 +8,6 @@ import (
 	"os"
 	"time"
 
-	"code.google.com/p/go-uuid/uuid"
 	"github.com/docker/distribution"
 	"github.com/docker/distribution/configuration"
 	ctxu "github.com/docker/distribution/context"
@@ -32,11 +31,8 @@ import (
 // fields should be protected.
 type App struct {
 	context.Context
-	Config configuration.Configuration
 
-	// InstanceID is a unique id assigned to the application on each creation.
-	// Provides information in the logs and context to identify restarts.
-	InstanceID string
+	Config configuration.Configuration
 
 	router           *mux.Router                 // main application router, configured with dispatchers
 	driver           storagedriver.StorageDriver // driver maintains the app global storage driver instance.
@@ -52,29 +48,17 @@ type App struct {
 	redis *redis.Pool
 }
 
-// Value intercepts calls context.Context.Value, returning the current app id,
-// if requested.
-func (app *App) Value(key interface{}) interface{} {
-	switch key {
-	case "app.id":
-		return app.InstanceID
-	}
-
-	return app.Context.Value(key)
-}
-
 // NewApp takes a configuration and returns a configured app, ready to serve
 // requests. The app only implements ServeHTTP and can be wrapped in other
 // handlers accordingly.
 func NewApp(ctx context.Context, configuration configuration.Configuration) *App {
 	app := &App{
-		Config:     configuration,
-		Context:    ctx,
-		InstanceID: uuid.New(),
-		router:     v2.RouterWithPrefix(configuration.HTTP.Prefix),
+		Config:  configuration,
+		Context: ctx,
+		router:  v2.RouterWithPrefix(configuration.HTTP.Prefix),
 	}
 
-	app.Context = ctxu.WithLogger(app.Context, ctxu.GetLogger(app, "app.id"))
+	app.Context = ctxu.WithLogger(app.Context, ctxu.GetLogger(app, "instance.id"))
 
 	// Register the handler dispatchers.
 	app.register(v2.RouteNameBase, func(ctx *Context, r *http.Request) http.Handler {
@@ -200,7 +184,7 @@ func (app *App) configureEvents(configuration *configuration.Configuration) {
 
 	app.events.source = notifications.SourceRecord{
 		Addr:       hostname,
-		InstanceID: app.InstanceID,
+		InstanceID: ctxu.GetStringValue(app, "instance.id"),
 	}
 }