Allow control over which storage cache to use

This allows one to better control the usage of the cache and turn it off
completely. The storage configuration module was modified to allow parameters
to be passed to just the storage implementation, rather than to the driver.

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

docs/handlers/app.go

@@ -103,11 +103,28 @@ func NewApp(ctx context.Context, configuration configuration.Configuration) *App
 	app.configureEvents(&configuration)
 	app.configureRedis(&configuration)
 
-	if app.redis != nil {
+	// configure storage caches
+	if cc, ok := configuration.Storage["cache"]; ok {
+		switch cc["layerinfo"] {
+		case "redis":
+			if app.redis == nil {
+				panic("redis configuration required to use for layerinfo cache")
+			}
 			app.registry = storage.NewRegistryWithDriver(app.driver, cache.NewRedisLayerInfoCache(app.redis))
-	} else {
+			ctxu.GetLogger(app).Infof("using redis layerinfo cache")
-		// always fall back to inmemory storage
+		case "inmemory":
 			app.registry = storage.NewRegistryWithDriver(app.driver, cache.NewInMemoryLayerInfoCache())
+			ctxu.GetLogger(app).Infof("using inmemory layerinfo cache")
+		default:
+			if cc["layerinfo"] != "" {
+				ctxu.GetLogger(app).Warnf("unkown cache type %q, caching disabled", configuration.Storage["cache"])
+			}
+		}
+	}
+
+	if app.registry == nil {
+		// configure the registry if no cache section is available.
+		app.registry = storage.NewRegistryWithDriver(app.driver, nil)
 	}
 
 	app.registry, err = applyRegistryMiddleware(app.registry, configuration.Middleware["registry"])