Merge pull request #465 from smarterclayton/simplify_config_for_reuse

Extract proxy/config common functions for reuse

cmd/proxy/proxy.go

@@ -41,27 +41,27 @@ func main() {
 
 	glog.Infof("Using configuration file %s and etcd_servers %s", *configFile, *etcdServers)
 
-	proxyConfig := config.NewServiceConfig()
+	serviceConfig := config.NewServiceConfig()
+	endpointsConfig := config.NewEndpointsConfig()
 
 	// Create a configuration source that handles configuration from etcd.
 	etcdClient := etcd.NewClient([]string{*etcdServers})
 	config.NewConfigSourceEtcd(etcdClient,
-		proxyConfig.GetServiceConfigurationChannel("etcd"),
+		serviceConfig.Channel("etcd"),
-		proxyConfig.GetEndpointsConfigurationChannel("etcd"))
+		endpointsConfig.Channel("etcd"))
 
 	// And create a configuration source that reads from a local file
 	config.NewConfigSourceFile(*configFile,
-		proxyConfig.GetServiceConfigurationChannel("file"),
+		serviceConfig.Channel("file"),
-		proxyConfig.GetEndpointsConfigurationChannel("file"))
+		endpointsConfig.Channel("file"))
 
 	loadBalancer := proxy.NewLoadBalancerRR()
 	proxier := proxy.NewProxier(loadBalancer)
 	// Wire proxier to handle changes to services
-	proxyConfig.RegisterServiceHandler(proxier)
+	serviceConfig.RegisterHandler(proxier)
 	// And wire loadBalancer to handle changes to endpoints to services
-	proxyConfig.RegisterEndpointsHandler(loadBalancer)
+	endpointsConfig.RegisterHandler(loadBalancer)
 
 	// Just loop forever for now...
 	select {}
-
 }

pkg/proxy/config/config.go

@@ -18,9 +18,9 @@ package config
 
 import (
 	"sync"
-	"time"
 
 	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/util/config"
 	"github.com/golang/glog"
 )
 
@@ -69,260 +69,200 @@ type EndpointsConfigHandler interface {
 	OnUpdate(endpoints []api.Endpoints)
 }
 
-// ServiceConfig tracks a set of service configurations and their endpoint configurations.
+// EndpointsConfig tracks a set of endpoints configurations.
-// It accepts "set", "add" and "remove" operations of services and endpoints via channels, and invokes registered handlers on change.
+// It accepts "set", "add" and "remove" operations of endpoints via channels, and invokes registered handlers on change.
+type EndpointsConfig struct {
+	mux     *config.Mux
+	watcher *config.Watcher
+	store   *endpointsStore
+}
+
+// NewEndpointConfig creates a new EndpointConfig.
+// It immediately runs the created EndpointConfig.
+func NewEndpointsConfig() *EndpointsConfig {
+	updates := make(chan struct{})
+	store := &endpointsStore{updates: updates, endpoints: make(map[string]map[string]api.Endpoints)}
+	mux := config.NewMux(store)
+	watcher := config.NewWatcher()
+	go watchForUpdates(watcher, store, updates)
+	return &EndpointsConfig{mux, watcher, store}
+}
+
+func (c *EndpointsConfig) RegisterHandler(handler EndpointsConfigHandler) {
+	c.watcher.Add(config.ListenerFunc(func(instance interface{}) {
+		handler.OnUpdate(instance.([]api.Endpoints))
+	}))
+}
+
+func (c *EndpointsConfig) Channel(source string) chan EndpointsUpdate {
+	ch := c.mux.Channel(source)
+	endpointsCh := make(chan EndpointsUpdate)
+	go func() {
+		for update := range endpointsCh {
+			ch <- update
+		}
+		close(ch)
+	}()
+	return endpointsCh
+}
+
+func (c *EndpointsConfig) Config() map[string]map[string]api.Endpoints {
+	return c.store.MergedState().(map[string]map[string]api.Endpoints)
+}
+
+type endpointsStore struct {
+	endpointLock sync.RWMutex
+	endpoints    map[string]map[string]api.Endpoints
+	updates      chan<- struct{}
+}
+
+func (s *endpointsStore) Merge(source string, change interface{}) error {
+	s.endpointLock.Lock()
+	endpoints := s.endpoints[source]
+	if endpoints == nil {
+		endpoints = make(map[string]api.Endpoints)
+	}
+	update := change.(EndpointsUpdate)
+	switch update.Op {
+	case ADD:
+		glog.Infof("Adding new endpoint from source %s : %v", source, update.Endpoints)
+		for _, value := range update.Endpoints {
+			endpoints[value.Name] = value
+		}
+	case REMOVE:
+		glog.Infof("Removing an endpoint %v", update)
+		for _, value := range update.Endpoints {
+			delete(endpoints, value.Name)
+		}
+	case SET:
+		glog.Infof("Setting endpoints %v", update)
+		// Clear the old map entries by just creating a new map
+		endpoints = make(map[string]api.Endpoints)
+		for _, value := range update.Endpoints {
+			endpoints[value.Name] = value
+		}
+	default:
+		glog.Infof("Received invalid update type: %v", update)
+	}
+	s.endpoints[source] = endpoints
+	s.endpointLock.Unlock()
+	if s.updates != nil {
+		s.updates <- struct{}{}
+	}
+	return nil
+}
+
+func (s *endpointsStore) MergedState() interface{} {
+	s.endpointLock.RLock()
+	defer s.endpointLock.RUnlock()
+	endpoints := make([]api.Endpoints, 0)
+	for _, sourceEndpoints := range s.endpoints {
+		for _, value := range sourceEndpoints {
+			endpoints = append(endpoints, value)
+		}
+	}
+	return endpoints
+}
+
+// ServiceConfig tracks a set of service configurations.
+// It accepts "set", "add" and "remove" operations of services via channels, and invokes registered handlers on change.
 type ServiceConfig struct {
-	// Configuration sources and their lock.
+	mux     *config.Mux
-	configSourceLock       sync.RWMutex
+	watcher *config.Watcher
-	serviceConfigSources   map[string]chan ServiceUpdate
+	store   *serviceStore
-	endpointsConfigSources map[string]chan EndpointsUpdate
-
-	// Handlers for changes to services and endpoints and their lock.
-	handlerLock      sync.RWMutex
-	serviceHandlers  []ServiceConfigHandler
-	endpointHandlers []EndpointsConfigHandler
-
-	// Last known configuration for union of the sources and the locks. Map goes
-	// from each source to array of services/endpoints that have been configured
-	// through that channel.
-	configLock     sync.RWMutex
-	serviceConfig  map[string]map[string]api.Service
-	endpointConfig map[string]map[string]api.Endpoints
-
-	// Channel that service configuration source listeners use to signal of new
-	// configurations.
-	// Value written is the source of the change.
-	serviceNotifyChannel chan string
-
-	// Channel that endpoint configuration source listeners use to signal of new
-	// configurations.
-	// Value written is the source of the change.
-	endpointsNotifyChannel chan string
 }
 
 // NewServiceConfig creates a new ServiceConfig.
 // It immediately runs the created ServiceConfig.
 func NewServiceConfig() *ServiceConfig {
-	config := &ServiceConfig{
+	updates := make(chan struct{})
-		serviceConfigSources:   make(map[string]chan ServiceUpdate),
+	store := &serviceStore{updates: updates, services: make(map[string]map[string]api.Service)}
-		endpointsConfigSources: make(map[string]chan EndpointsUpdate),
+	mux := config.NewMux(store)
-		serviceHandlers:        make([]ServiceConfigHandler, 10),
+	watcher := config.NewWatcher()
-		endpointHandlers:       make([]EndpointsConfigHandler, 10),
+	go watchForUpdates(watcher, store, updates)
-		serviceConfig:          make(map[string]map[string]api.Service),
+	return &ServiceConfig{mux, watcher, store}
-		endpointConfig:         make(map[string]map[string]api.Endpoints),
-		serviceNotifyChannel:   make(chan string),
-		endpointsNotifyChannel: make(chan string),
-	}
-	go config.Run()
-	return config
 }
 
-// Run begins a loop to accept new service configurations and new endpoint configurations.
+func (c *ServiceConfig) RegisterHandler(handler ServiceConfigHandler) {
-// It never returns.
+	c.watcher.Add(config.ListenerFunc(func(instance interface{}) {
-func (impl *ServiceConfig) Run() {
+		handler.OnUpdate(instance.([]api.Service))
-	glog.Infof("Starting the config Run loop")
+	}))
-	for {
-		select {
-		case source := <-impl.serviceNotifyChannel:
-			glog.Infof("Got new service configuration from source %s", source)
-			impl.notifyServiceUpdate()
-		case source := <-impl.endpointsNotifyChannel:
-			glog.Infof("Got new endpoint configuration from source %s", source)
-			impl.notifyEndpointsUpdate()
-		case <-time.After(1 * time.Second):
-		}
-	}
 }
 
-// serviceChannelListener begins a loop to handle incoming ServiceUpdate notifications from the channel.
+func (c *ServiceConfig) Channel(source string) chan ServiceUpdate {
-// It never returns.
+	ch := c.mux.Channel(source)
-func (impl *ServiceConfig) serviceChannelListener(source string, listenChannel chan ServiceUpdate) {
+	serviceCh := make(chan ServiceUpdate)
-	// Represents the current services configuration for this channel.
+	go func() {
-	serviceMap := make(map[string]api.Service)
+		for update := range serviceCh {
-	for {
+			ch <- update
-		select {
+		}
-		case update := <-listenChannel:
+		close(ch)
-			impl.configLock.Lock()
+	}()
+	return serviceCh
+}
+
+func (c *ServiceConfig) Config() map[string]map[string]api.Service {
+	return c.store.MergedState().(map[string]map[string]api.Service)
+}
+
+type serviceStore struct {
+	serviceLock sync.RWMutex
+	services    map[string]map[string]api.Service
+	updates     chan<- struct{}
+}
+
+func (s *serviceStore) Merge(source string, change interface{}) error {
+	s.serviceLock.Lock()
+	services := s.services[source]
+	if services == nil {
+		services = make(map[string]api.Service)
+	}
+	update := change.(ServiceUpdate)
 	switch update.Op {
 	case ADD:
 		glog.Infof("Adding new service from source %s : %v", source, update.Services)
 		for _, value := range update.Services {
-					serviceMap[value.ID] = value
+			services[value.ID] = value
 		}
 	case REMOVE:
 		glog.Infof("Removing a service %v", update)
 		for _, value := range update.Services {
-					delete(serviceMap, value.ID)
+			delete(services, value.ID)
 		}
 	case SET:
 		glog.Infof("Setting services %v", update)
 		// Clear the old map entries by just creating a new map
-				serviceMap = make(map[string]api.Service)
+		services = make(map[string]api.Service)
 		for _, value := range update.Services {
-					serviceMap[value.ID] = value
+			services[value.ID] = value
 		}
 	default:
 		glog.Infof("Received invalid update type: %v", update)
-				continue
-			}
-			impl.serviceConfig[source] = serviceMap
-			impl.configLock.Unlock()
-			impl.serviceNotifyChannel <- source
 	}
+	s.services[source] = services
+	s.serviceLock.Unlock()
+	if s.updates != nil {
+		s.updates <- struct{}{}
 	}
+	return nil
 }
 
-// endpointsChannelListener begins a loop to handle incoming EndpointsUpdate notifications from the channel.
+func (s *serviceStore) MergedState() interface{} {
-// It never returns.
+	s.serviceLock.RLock()
-func (impl *ServiceConfig) endpointsChannelListener(source string, listenChannel chan EndpointsUpdate) {
+	defer s.serviceLock.RUnlock()
-	endpointMap := make(map[string]api.Endpoints)
+	services := make([]api.Service, 0)
-	for {
+	for _, sourceServices := range s.services {
-		select {
-		case update := <-listenChannel:
-			impl.configLock.Lock()
-			switch update.Op {
-			case ADD:
-				glog.Infof("Adding a new endpoint %v", update)
-				for _, value := range update.Endpoints {
-					endpointMap[value.Name] = value
-				}
-			case REMOVE:
-				glog.Infof("Removing an endpoint %v", update)
-				for _, value := range update.Endpoints {
-					delete(endpointMap, value.Name)
-				}
-
-			case SET:
-				glog.Infof("Setting services %v", update)
-				// Clear the old map entries by just creating a new map
-				endpointMap = make(map[string]api.Endpoints)
-				for _, value := range update.Endpoints {
-					endpointMap[value.Name] = value
-				}
-			default:
-				glog.Infof("Received invalid update type: %v", update)
-				continue
-			}
-			impl.endpointConfig[source] = endpointMap
-			impl.configLock.Unlock()
-			impl.endpointsNotifyChannel <- source
-		}
-
-	}
-}
-
-// GetServiceConfigurationChannel returns a channel where a configuration source
-// can send updates of new service configurations. Multiple calls with the same
-// source will return the same channel. This allows change and state based sources
-// to use the same channel. Difference source names however will be treated as a
-// union.
-func (impl *ServiceConfig) GetServiceConfigurationChannel(source string) chan ServiceUpdate {
-	if len(source) == 0 {
-		panic("GetServiceConfigurationChannel given an empty service name")
-	}
-	impl.configSourceLock.Lock()
-	defer impl.configSourceLock.Unlock()
-	channel, exists := impl.serviceConfigSources[source]
-	if exists {
-		return channel
-	}
-	newChannel := make(chan ServiceUpdate)
-	impl.serviceConfigSources[source] = newChannel
-	go impl.serviceChannelListener(source, newChannel)
-	return newChannel
-}
-
-// GetEndpointsConfigurationChannel returns a channel where a configuration source
-// can send updates of new endpoint configurations. Multiple calls with the same
-// source will return the same channel. This allows change and state based sources
-// to use the same channel. Difference source names however will be treated as a
-// union.
-func (impl *ServiceConfig) GetEndpointsConfigurationChannel(source string) chan EndpointsUpdate {
-	if len(source) == 0 {
-		panic("GetEndpointConfigurationChannel given an empty service name")
-	}
-	impl.configSourceLock.Lock()
-	defer impl.configSourceLock.Unlock()
-	channel, exists := impl.endpointsConfigSources[source]
-	if exists {
-		return channel
-	}
-	newChannel := make(chan EndpointsUpdate)
-	impl.endpointsConfigSources[source] = newChannel
-	go impl.endpointsChannelListener(source, newChannel)
-	return newChannel
-}
-
-// RegisterServiceHandler registers the ServiceConfigHandler to receive updates of changes to services.
-func (impl *ServiceConfig) RegisterServiceHandler(handler ServiceConfigHandler) {
-	impl.handlerLock.Lock()
-	defer impl.handlerLock.Unlock()
-	for i, h := range impl.serviceHandlers {
-		if h == nil {
-			impl.serviceHandlers[i] = handler
-			return
-		}
-	}
-	// TODO(vaikas): Grow the array here instead of panic.
-	// In practice we are expecting there to be 1 handler anyways,
-	// so not a big deal for now
-	panic("Only up to 10 service handlers supported for now")
-}
-
-// RegisterEndpointsHandler registers the EndpointsConfigHandler to receive updates of changes to services.
-func (impl *ServiceConfig) RegisterEndpointsHandler(handler EndpointsConfigHandler) {
-	impl.handlerLock.Lock()
-	defer impl.handlerLock.Unlock()
-	for i, h := range impl.endpointHandlers {
-		if h == nil {
-			impl.endpointHandlers[i] = handler
-			return
-		}
-	}
-	// TODO(vaikas): Grow the array here instead of panic.
-	// In practice we are expecting there to be 1 handler anyways,
-	// so not a big deal for now
-	panic("Only up to 10 endpoint handlers supported for now")
-}
-
-// notifyServiceUpdate calls the registered ServiceConfigHandlers with the current states of services.
-func (impl *ServiceConfig) notifyServiceUpdate() {
-	services := []api.Service{}
-	impl.configLock.RLock()
-	for _, sourceServices := range impl.serviceConfig {
 		for _, value := range sourceServices {
 			services = append(services, value)
 		}
 	}
-	impl.configLock.RUnlock()
+	return services
-	glog.Infof("Unified configuration %+v", services)
-	impl.handlerLock.RLock()
-	handlers := impl.serviceHandlers
-	impl.handlerLock.RUnlock()
-	for _, handler := range handlers {
-		if handler != nil {
-			handler.OnUpdate(services)
-		}
-	}
 }
 
-// notifyEndpointsUpdate calls the registered EndpointsConfigHandlers with the current states of endpoints.
+// watchForUpdates invokes watcher.Notify() with the latest version of an object
-func (impl *ServiceConfig) notifyEndpointsUpdate() {
+// when changes occur.
-	endpoints := []api.Endpoints{}
+func watchForUpdates(watcher *config.Watcher, accessor config.Accessor, updates <-chan struct{}) {
-	impl.configLock.RLock()
+	for _ = range updates {
-	for _, sourceEndpoints := range impl.endpointConfig {
+		watcher.Notify(accessor.MergedState())
-		for _, value := range sourceEndpoints {
-			endpoints = append(endpoints, value)
-		}
-	}
-	impl.configLock.RUnlock()
-	glog.Infof("Unified configuration %+v", endpoints)
-	impl.handlerLock.RLock()
-	handlers := impl.endpointHandlers
-	impl.handlerLock.RUnlock()
-	for _, handler := range handlers {
-		if handler != nil {
-			handler.OnUpdate(endpoints)
-		}
 	}
 }

pkg/proxy/config/config_test.go

@@ -14,13 +14,16 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-package config
+package config_test
 
 import (
 	"reflect"
+	"sort"
+	"sync"
 	"testing"
 
 	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
+	. "github.com/GoogleCloudPlatform/kubernetes/pkg/proxy/config"
 )
 
 const TomcatPort int = 8080
@@ -33,42 +36,82 @@ const MysqlName = "mysql"
 
 var MysqlEndpoints = map[string]string{"c0": "1.1.1.1:13306", "c3": "2.2.2.2:13306"}
 
+type sortedServices []api.Service
+
+func (s sortedServices) Len() int {
+	return len(s)
+}
+func (s sortedServices) Swap(i, j int) {
+	s[i], s[j] = s[j], s[i]
+}
+func (s sortedServices) Less(i, j int) bool {
+	return s[i].JSONBase.ID < s[j].JSONBase.ID
+}
+
 type ServiceHandlerMock struct {
 	services []api.Service
+	updated  sync.WaitGroup
 }
 
-func NewServiceHandlerMock() ServiceHandlerMock {
+func NewServiceHandlerMock() *ServiceHandlerMock {
-	return ServiceHandlerMock{services: make([]api.Service, 0)}
+	return &ServiceHandlerMock{services: make([]api.Service, 0)}
 }
 
-func (impl ServiceHandlerMock) OnUpdate(services []api.Service) {
+func (h *ServiceHandlerMock) OnUpdate(services []api.Service) {
-	impl.services = services
+	sort.Sort(sortedServices(services))
+	h.services = services
+	h.updated.Done()
 }
 
-func (impl ServiceHandlerMock) ValidateServices(t *testing.T, expectedServices []api.Service) {
+func (h *ServiceHandlerMock) ValidateServices(t *testing.T, expectedServices []api.Service) {
-	if reflect.DeepEqual(impl.services, expectedServices) {
+	h.updated.Wait()
-		t.Errorf("Services don't match %+v expected: %+v", impl.services, expectedServices)
+	if !reflect.DeepEqual(h.services, expectedServices) {
+		t.Errorf("Expected %#v, Got %#v", expectedServices, h.services)
 	}
 }
 
+func (h *ServiceHandlerMock) Wait(waits int) {
+	h.updated.Add(waits)
+}
+
+type sortedEndpoints []api.Endpoints
+
+func (s sortedEndpoints) Len() int {
+	return len(s)
+}
+func (s sortedEndpoints) Swap(i, j int) {
+	s[i], s[j] = s[j], s[i]
+}
+func (s sortedEndpoints) Less(i, j int) bool {
+	return s[i].Name < s[j].Name
+}
+
 type EndpointsHandlerMock struct {
 	endpoints []api.Endpoints
+	updated   sync.WaitGroup
 }
 
-func NewEndpointsHandlerMock() EndpointsHandlerMock {
+func NewEndpointsHandlerMock() *EndpointsHandlerMock {
-	return EndpointsHandlerMock{endpoints: make([]api.Endpoints, 0)}
+	return &EndpointsHandlerMock{endpoints: make([]api.Endpoints, 0)}
 }
 
-func (impl EndpointsHandlerMock) OnUpdate(endpoints []api.Endpoints) {
+func (h *EndpointsHandlerMock) OnUpdate(endpoints []api.Endpoints) {
-	impl.endpoints = endpoints
+	sort.Sort(sortedEndpoints(endpoints))
+	h.endpoints = endpoints
+	h.updated.Done()
 }
 
-func (impl EndpointsHandlerMock) ValidateEndpoints(t *testing.T, expectedEndpoints []api.Endpoints) {
+func (h *EndpointsHandlerMock) ValidateEndpoints(t *testing.T, expectedEndpoints []api.Endpoints) {
-	if reflect.DeepEqual(impl.endpoints, expectedEndpoints) {
+	h.updated.Wait()
-		t.Errorf("Endpoints don't match %+v", impl.endpoints, expectedEndpoints)
+	if !reflect.DeepEqual(h.endpoints, expectedEndpoints) {
+		t.Errorf("Expected %#v, Got %#v", expectedEndpoints, h.endpoints)
 	}
 }
 
+func (h *EndpointsHandlerMock) Wait(waits int) {
+	h.updated.Add(waits)
+}
+
 func CreateServiceUpdate(op Operation, services ...api.Service) ServiceUpdate {
 	ret := ServiceUpdate{Op: op}
 	ret.Services = make([]api.Service, len(services))
@@ -87,35 +130,12 @@ func CreateEndpointsUpdate(op Operation, endpoints ...api.Endpoints) EndpointsUp
 	return ret
 }
 
-func TestServiceConfigurationChannels(t *testing.T) {
-	config := NewServiceConfig()
-	channelOne := config.GetServiceConfigurationChannel("one")
-	if channelOne != config.GetServiceConfigurationChannel("one") {
-		t.Error("Didn't get the same service configuration channel back with the same name")
-	}
-	channelTwo := config.GetServiceConfigurationChannel("two")
-	if channelOne == channelTwo {
-		t.Error("Got back the same service configuration channel for different names")
-	}
-}
-
-func TestEndpointConfigurationChannels(t *testing.T) {
-	config := NewServiceConfig()
-	channelOne := config.GetEndpointsConfigurationChannel("one")
-	if channelOne != config.GetEndpointsConfigurationChannel("one") {
-		t.Error("Didn't get the same endpoint configuration channel back with the same name")
-	}
-	channelTwo := config.GetEndpointsConfigurationChannel("two")
-	if channelOne == channelTwo {
-		t.Error("Got back the same endpoint configuration channel for different names")
-	}
-}
-
 func TestNewServiceAddedAndNotified(t *testing.T) {
 	config := NewServiceConfig()
-	channel := config.GetServiceConfigurationChannel("one")
+	channel := config.Channel("one")
 	handler := NewServiceHandlerMock()
-	config.RegisterServiceHandler(&handler)
+	handler.Wait(1)
+	config.RegisterHandler(handler)
 	serviceUpdate := CreateServiceUpdate(ADD, api.Service{JSONBase: api.JSONBase{ID: "foo"}, Port: 10})
 	channel <- serviceUpdate
 	handler.ValidateServices(t, serviceUpdate.Services)
@@ -124,24 +144,28 @@ func TestNewServiceAddedAndNotified(t *testing.T) {
 
 func TestServiceAddedRemovedSetAndNotified(t *testing.T) {
 	config := NewServiceConfig()
-	channel := config.GetServiceConfigurationChannel("one")
+	channel := config.Channel("one")
 	handler := NewServiceHandlerMock()
-	config.RegisterServiceHandler(&handler)
+	config.RegisterHandler(handler)
 	serviceUpdate := CreateServiceUpdate(ADD, api.Service{JSONBase: api.JSONBase{ID: "foo"}, Port: 10})
+	handler.Wait(1)
 	channel <- serviceUpdate
 	handler.ValidateServices(t, serviceUpdate.Services)
 
 	serviceUpdate2 := CreateServiceUpdate(ADD, api.Service{JSONBase: api.JSONBase{ID: "bar"}, Port: 20})
+	handler.Wait(1)
 	channel <- serviceUpdate2
-	services := []api.Service{serviceUpdate.Services[0], serviceUpdate2.Services[0]}
+	services := []api.Service{serviceUpdate2.Services[0], serviceUpdate.Services[0]}
 	handler.ValidateServices(t, services)
 
 	serviceUpdate3 := CreateServiceUpdate(REMOVE, api.Service{JSONBase: api.JSONBase{ID: "foo"}})
+	handler.Wait(1)
 	channel <- serviceUpdate3
 	services = []api.Service{serviceUpdate2.Services[0]}
 	handler.ValidateServices(t, services)
 
 	serviceUpdate4 := CreateServiceUpdate(SET, api.Service{JSONBase: api.JSONBase{ID: "foobar"}, Port: 99})
+	handler.Wait(1)
 	channel <- serviceUpdate4
 	services = []api.Service{serviceUpdate4.Services[0]}
 	handler.ValidateServices(t, services)
@@ -149,89 +173,102 @@ func TestServiceAddedRemovedSetAndNotified(t *testing.T) {
 
 func TestNewMultipleSourcesServicesAddedAndNotified(t *testing.T) {
 	config := NewServiceConfig()
-	channelOne := config.GetServiceConfigurationChannel("one")
+	channelOne := config.Channel("one")
-	channelTwo := config.GetServiceConfigurationChannel("two")
+	channelTwo := config.Channel("two")
 	if channelOne == channelTwo {
 		t.Error("Same channel handed back for one and two")
 	}
 	handler := NewServiceHandlerMock()
-	config.RegisterServiceHandler(handler)
+	config.RegisterHandler(handler)
 	serviceUpdate1 := CreateServiceUpdate(ADD, api.Service{JSONBase: api.JSONBase{ID: "foo"}, Port: 10})
 	serviceUpdate2 := CreateServiceUpdate(ADD, api.Service{JSONBase: api.JSONBase{ID: "bar"}, Port: 20})
+	handler.Wait(2)
 	channelOne <- serviceUpdate1
 	channelTwo <- serviceUpdate2
-	services := []api.Service{serviceUpdate1.Services[0], serviceUpdate2.Services[0]}
+	services := []api.Service{serviceUpdate2.Services[0], serviceUpdate1.Services[0]}
 	handler.ValidateServices(t, services)
 }
 
 func TestNewMultipleSourcesServicesMultipleHandlersAddedAndNotified(t *testing.T) {
 	config := NewServiceConfig()
-	channelOne := config.GetServiceConfigurationChannel("one")
+	channelOne := config.Channel("one")
-	channelTwo := config.GetServiceConfigurationChannel("two")
+	channelTwo := config.Channel("two")
 	handler := NewServiceHandlerMock()
 	handler2 := NewServiceHandlerMock()
-	config.RegisterServiceHandler(handler)
+	config.RegisterHandler(handler)
-	config.RegisterServiceHandler(handler2)
+	config.RegisterHandler(handler2)
 	serviceUpdate1 := CreateServiceUpdate(ADD, api.Service{JSONBase: api.JSONBase{ID: "foo"}, Port: 10})
 	serviceUpdate2 := CreateServiceUpdate(ADD, api.Service{JSONBase: api.JSONBase{ID: "bar"}, Port: 20})
+	handler.Wait(2)
+	handler2.Wait(2)
 	channelOne <- serviceUpdate1
 	channelTwo <- serviceUpdate2
-	services := []api.Service{serviceUpdate1.Services[0], serviceUpdate2.Services[0]}
+	services := []api.Service{serviceUpdate2.Services[0], serviceUpdate1.Services[0]}
 	handler.ValidateServices(t, services)
 	handler2.ValidateServices(t, services)
 }
 
 func TestNewMultipleSourcesEndpointsMultipleHandlersAddedAndNotified(t *testing.T) {
-	config := NewServiceConfig()
+	config := NewEndpointsConfig()
-	channelOne := config.GetEndpointsConfigurationChannel("one")
+	channelOne := config.Channel("one")
-	channelTwo := config.GetEndpointsConfigurationChannel("two")
+	channelTwo := config.Channel("two")
 	handler := NewEndpointsHandlerMock()
 	handler2 := NewEndpointsHandlerMock()
-	config.RegisterEndpointsHandler(handler)
+	config.RegisterHandler(handler)
-	config.RegisterEndpointsHandler(handler2)
+	config.RegisterHandler(handler2)
 	endpointsUpdate1 := CreateEndpointsUpdate(ADD, api.Endpoints{Name: "foo", Endpoints: []string{"endpoint1", "endpoint2"}})
 	endpointsUpdate2 := CreateEndpointsUpdate(ADD, api.Endpoints{Name: "bar", Endpoints: []string{"endpoint3", "endpoint4"}})
+	handler.Wait(2)
+	handler2.Wait(2)
 	channelOne <- endpointsUpdate1
 	channelTwo <- endpointsUpdate2
 
-	endpoints := []api.Endpoints{endpointsUpdate1.Endpoints[0], endpointsUpdate2.Endpoints[0]}
+	endpoints := []api.Endpoints{endpointsUpdate2.Endpoints[0], endpointsUpdate1.Endpoints[0]}
 	handler.ValidateEndpoints(t, endpoints)
 	handler2.ValidateEndpoints(t, endpoints)
 }
 
 func TestNewMultipleSourcesEndpointsMultipleHandlersAddRemoveSetAndNotified(t *testing.T) {
-	config := NewServiceConfig()
+	config := NewEndpointsConfig()
-	channelOne := config.GetEndpointsConfigurationChannel("one")
+	channelOne := config.Channel("one")
-	channelTwo := config.GetEndpointsConfigurationChannel("two")
+	channelTwo := config.Channel("two")
 	handler := NewEndpointsHandlerMock()
 	handler2 := NewEndpointsHandlerMock()
-	config.RegisterEndpointsHandler(handler)
+	config.RegisterHandler(handler)
-	config.RegisterEndpointsHandler(handler2)
+	config.RegisterHandler(handler2)
 	endpointsUpdate1 := CreateEndpointsUpdate(ADD, api.Endpoints{Name: "foo", Endpoints: []string{"endpoint1", "endpoint2"}})
 	endpointsUpdate2 := CreateEndpointsUpdate(ADD, api.Endpoints{Name: "bar", Endpoints: []string{"endpoint3", "endpoint4"}})
+	handler.Wait(2)
+	handler2.Wait(2)
 	channelOne <- endpointsUpdate1
 	channelTwo <- endpointsUpdate2
 
-	endpoints := []api.Endpoints{endpointsUpdate1.Endpoints[0], endpointsUpdate2.Endpoints[0]}
+	endpoints := []api.Endpoints{endpointsUpdate2.Endpoints[0], endpointsUpdate1.Endpoints[0]}
 	handler.ValidateEndpoints(t, endpoints)
 	handler2.ValidateEndpoints(t, endpoints)
 
 	// Add one more
 	endpointsUpdate3 := CreateEndpointsUpdate(ADD, api.Endpoints{Name: "foobar", Endpoints: []string{"endpoint5", "endpoint6"}})
+	handler.Wait(1)
+	handler2.Wait(1)
 	channelTwo <- endpointsUpdate3
-	endpoints = []api.Endpoints{endpointsUpdate1.Endpoints[0], endpointsUpdate2.Endpoints[0], endpointsUpdate3.Endpoints[0]}
+	endpoints = []api.Endpoints{endpointsUpdate2.Endpoints[0], endpointsUpdate1.Endpoints[0], endpointsUpdate3.Endpoints[0]}
 	handler.ValidateEndpoints(t, endpoints)
 	handler2.ValidateEndpoints(t, endpoints)
 
 	// Update the "foo" service with new endpoints
 	endpointsUpdate1 = CreateEndpointsUpdate(ADD, api.Endpoints{Name: "foo", Endpoints: []string{"endpoint77"}})
+	handler.Wait(1)
+	handler2.Wait(1)
 	channelOne <- endpointsUpdate1
-	endpoints = []api.Endpoints{endpointsUpdate1.Endpoints[0], endpointsUpdate2.Endpoints[0], endpointsUpdate3.Endpoints[0]}
+	endpoints = []api.Endpoints{endpointsUpdate2.Endpoints[0], endpointsUpdate1.Endpoints[0], endpointsUpdate3.Endpoints[0]}
 	handler.ValidateEndpoints(t, endpoints)
 	handler2.ValidateEndpoints(t, endpoints)
 
 	// Remove "bar" service
 	endpointsUpdate2 = CreateEndpointsUpdate(REMOVE, api.Endpoints{Name: "bar"})
+	handler.Wait(1)
+	handler2.Wait(1)
 	channelTwo <- endpointsUpdate2
 
 	endpoints = []api.Endpoints{endpointsUpdate1.Endpoints[0], endpointsUpdate3.Endpoints[0]}

pkg/proxy/config/etcd.go

@@ -66,13 +66,13 @@ func NewConfigSourceEtcd(client *etcd.Client, serviceChannel chan ServiceUpdate,
 }
 
 // Run begins watching for new services and their endpoints on etcd.
-func (impl ConfigSourceEtcd) Run() {
+func (s ConfigSourceEtcd) Run() {
 	// Initially, just wait for the etcd to come up before doing anything more complicated.
 	var services []api.Service
 	var endpoints []api.Endpoints
 	var err error
 	for {
-		services, endpoints, err = impl.getServices()
+		services, endpoints, err = s.GetServices()
 		if err == nil {
 			break
 		}
@@ -82,39 +82,39 @@ func (impl ConfigSourceEtcd) Run() {
 
 	if len(services) > 0 {
 		serviceUpdate := ServiceUpdate{Op: SET, Services: services}
-		impl.serviceChannel <- serviceUpdate
+		s.serviceChannel <- serviceUpdate
 	}
 	if len(endpoints) > 0 {
 		endpointsUpdate := EndpointsUpdate{Op: SET, Endpoints: endpoints}
-		impl.endpointsChannel <- endpointsUpdate
+		s.endpointsChannel <- endpointsUpdate
 	}
 
 	// Ok, so we got something back from etcd. Let's set up a watch for new services, and
 	// their endpoints
-	go impl.watchForChanges()
+	go s.WatchForChanges()
 
 	for {
-		services, endpoints, err = impl.getServices()
+		services, endpoints, err = s.GetServices()
 		if err != nil {
 			glog.Errorf("ConfigSourceEtcd: Failed to get services: %v", err)
 		} else {
 			if len(services) > 0 {
 				serviceUpdate := ServiceUpdate{Op: SET, Services: services}
-				impl.serviceChannel <- serviceUpdate
+				s.serviceChannel <- serviceUpdate
 			}
 			if len(endpoints) > 0 {
 				endpointsUpdate := EndpointsUpdate{Op: SET, Endpoints: endpoints}
-				impl.endpointsChannel <- endpointsUpdate
+				s.endpointsChannel <- endpointsUpdate
 			}
 		}
 		time.Sleep(30 * time.Second)
 	}
 }
 
-// getServices finds the list of services and their endpoints from etcd.
+// GetServices finds the list of services and their endpoints from etcd.
 // This operation is akin to a set a known good at regular intervals.
-func (impl ConfigSourceEtcd) getServices() ([]api.Service, []api.Endpoints, error) {
+func (s ConfigSourceEtcd) GetServices() ([]api.Service, []api.Endpoints, error) {
-	response, err := impl.client.Get(registryRoot+"/specs", true, false)
+	response, err := s.client.Get(registryRoot+"/specs", true, false)
 	if err != nil {
 		glog.Errorf("Failed to get the key %s: %v", registryRoot, err)
 		return make([]api.Service, 0), make([]api.Endpoints, 0), err
@@ -133,7 +133,7 @@ func (impl ConfigSourceEtcd) getServices() ([]api.Service, []api.Endpoints, erro
 				continue
 			}
 			retServices[i] = svc
-			endpoints, err := impl.getEndpoints(svc.ID)
+			endpoints, err := s.GetEndpoints(svc.ID)
 			if err != nil {
 				glog.Errorf("Couldn't get endpoints for %s : %v skipping", svc.ID, err)
 			}
@@ -145,10 +145,10 @@ func (impl ConfigSourceEtcd) getServices() ([]api.Service, []api.Endpoints, erro
 	return nil, nil, fmt.Errorf("did not get the root of the registry %s", registryRoot)
 }
 
-// getEndpoints finds the list of endpoints of the service from etcd.
+// GetEndpoints finds the list of endpoints of the service from etcd.
-func (impl ConfigSourceEtcd) getEndpoints(service string) (api.Endpoints, error) {
+func (s ConfigSourceEtcd) GetEndpoints(service string) (api.Endpoints, error) {
 	key := fmt.Sprintf(registryRoot + "/endpoints/" + service)
-	response, err := impl.client.Get(key, true, false)
+	response, err := s.client.Get(key, true, false)
 	if err != nil {
 		glog.Errorf("Failed to get the key: %s %v", key, err)
 		return api.Endpoints{}, err
@@ -176,23 +176,23 @@ func parseEndpoints(jsonString string) (api.Endpoints, error) {
 	return e, err
 }
 
-func (impl ConfigSourceEtcd) watchForChanges() {
+func (s ConfigSourceEtcd) WatchForChanges() {
 	glog.Info("Setting up a watch for new services")
 	watchChannel := make(chan *etcd.Response)
-	go impl.client.Watch("/registry/services/", 0, true, watchChannel, nil)
+	go s.client.Watch("/registry/services/", 0, true, watchChannel, nil)
 	for {
 		watchResponse := <-watchChannel
-		impl.processChange(watchResponse)
+		s.ProcessChange(watchResponse)
 	}
 }
 
-func (impl ConfigSourceEtcd) processChange(response *etcd.Response) {
+func (s ConfigSourceEtcd) ProcessChange(response *etcd.Response) {
 	glog.Infof("Processing a change in service configuration... %s", *response)
 
 	// If it's a new service being added (signified by a localport being added)
 	// then process it as such
 	if strings.Contains(response.Node.Key, "/endpoints/") {
-		impl.processEndpointResponse(response)
+		s.ProcessEndpointResponse(response)
 	} else if response.Action == "set" {
 		service, err := etcdResponseToService(response)
 		if err != nil {
@@ -202,7 +202,7 @@ func (impl ConfigSourceEtcd) processChange(response *etcd.Response) {
 
 		glog.Infof("New service added/updated: %#v", service)
 		serviceUpdate := ServiceUpdate{Op: ADD, Services: []api.Service{*service}}
-		impl.serviceChannel <- serviceUpdate
+		s.serviceChannel <- serviceUpdate
 		return
 	}
 	if response.Action == "delete" {
@@ -210,14 +210,14 @@ func (impl ConfigSourceEtcd) processChange(response *etcd.Response) {
 		if len(parts) == 4 {
 			glog.Infof("Deleting service: %s", parts[3])
 			serviceUpdate := ServiceUpdate{Op: REMOVE, Services: []api.Service{{JSONBase: api.JSONBase{ID: parts[3]}}}}
-			impl.serviceChannel <- serviceUpdate
+			s.serviceChannel <- serviceUpdate
 			return
 		}
 		glog.Infof("Unknown service delete: %#v", parts)
 	}
 }
 
-func (impl ConfigSourceEtcd) processEndpointResponse(response *etcd.Response) {
+func (s ConfigSourceEtcd) ProcessEndpointResponse(response *etcd.Response) {
 	glog.Infof("Processing a change in endpoint configuration... %s", *response)
 	var endpoints api.Endpoints
 	err := json.Unmarshal([]byte(response.Node.Value), &endpoints)
@@ -226,5 +226,5 @@ func (impl ConfigSourceEtcd) processEndpointResponse(response *etcd.Response) {
 		return
 	}
 	endpointsUpdate := EndpointsUpdate{Op: ADD, Endpoints: []api.Endpoints{endpoints}}
-	impl.endpointsChannel <- endpointsUpdate
+	s.endpointsChannel <- endpointsUpdate
 }

pkg/proxy/config/file.go

@@ -70,16 +70,16 @@ func NewConfigSourceFile(filename string, serviceChannel chan ServiceUpdate, end
 }
 
 // Run begins watching the config file.
-func (impl ConfigSourceFile) Run() {
+func (s ConfigSourceFile) Run() {
-	glog.Infof("Watching file %s", impl.filename)
+	glog.Infof("Watching file %s", s.filename)
 	var lastData []byte
 	var lastServices []api.Service
 	var lastEndpoints []api.Endpoints
 
 	for {
-		data, err := ioutil.ReadFile(impl.filename)
+		data, err := ioutil.ReadFile(s.filename)
 		if err != nil {
-			glog.Errorf("Couldn't read file: %s : %v", impl.filename, err)
+			glog.Errorf("Couldn't read file: %s : %v", s.filename, err)
 			continue
 		}
 
@@ -103,12 +103,12 @@ func (impl ConfigSourceFile) Run() {
 		}
 		if !reflect.DeepEqual(lastServices, newServices) {
 			serviceUpdate := ServiceUpdate{Op: SET, Services: newServices}
-			impl.serviceChannel <- serviceUpdate
+			s.serviceChannel <- serviceUpdate
 			lastServices = newServices
 		}
 		if !reflect.DeepEqual(lastEndpoints, newEndpoints) {
 			endpointsUpdate := EndpointsUpdate{Op: SET, Endpoints: newEndpoints}
-			impl.endpointsChannel <- endpointsUpdate
+			s.endpointsChannel <- endpointsUpdate
 			lastEndpoints = newEndpoints
 		}
 

pkg/util/config/config.go

@@ -0,0 +1,140 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or cied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package config
+
+import (
+	"sync"
+
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/util"
+)
+
+type Merger interface {
+	// Invoked when a change from a source is received.  May also function as an incremental
+	// merger if you wish to consume changes incrementally.  Must be reentrant when more than
+	// one source is defined.
+	Merge(source string, update interface{}) error
+}
+
+// MergeFunc implements the Merger interface
+type MergeFunc func(source string, update interface{}) error
+
+func (f MergeFunc) Merge(source string, update interface{}) error {
+	return f(source, update)
+}
+
+// Mux is a class for merging configuration from multiple sources.  Changes are
+// pushed via channels and sent to the merge function.
+type Mux struct {
+	// Invoked when an update is sent to a source.
+	merger Merger
+
+	// Sources and their lock.
+	sourceLock sync.RWMutex
+	// Maps source names to channels
+	sources map[string]chan interface{}
+}
+
+// NewMux creates a new mux that can merge changes from multiple sources.
+func NewMux(merger Merger) *Mux {
+	mux := &Mux{
+		sources: make(map[string]chan interface{}),
+		merger:  merger,
+	}
+	return mux
+}
+
+// Channel returns a channel where a configuration source
+// can send updates of new configurations. Multiple calls with the same
+// source will return the same channel. This allows change and state based sources
+// to use the same channel. Different source names however will be treated as a
+// union.
+func (m *Mux) Channel(source string) chan interface{} {
+	if len(source) == 0 {
+		panic("Channel given an empty name")
+	}
+	m.sourceLock.Lock()
+	defer m.sourceLock.Unlock()
+	channel, exists := m.sources[source]
+	if exists {
+		return channel
+	}
+	newChannel := make(chan interface{})
+	m.sources[source] = newChannel
+	go util.Forever(func() { m.listen(source, newChannel) }, 0)
+	return newChannel
+}
+
+func (m *Mux) listen(source string, listenChannel <-chan interface{}) {
+	for update := range listenChannel {
+		m.merger.Merge(source, update)
+	}
+}
+
+// Accessor is an interface for retrieving the current merge state.
+type Accessor interface {
+	// MergedState returns a representation of the current merge state.
+	// Must be reentrant when more than one source is defined.
+	MergedState() interface{}
+}
+
+// AccessorFunc implements the Accessor interface
+type AccessorFunc func() interface{}
+
+func (f AccessorFunc) MergedState() interface{} {
+	return f()
+}
+
+type Listener interface {
+	// OnUpdate is invoked when a change is made to an object.
+	OnUpdate(instance interface{})
+}
+
+// ListenerFunc receives a representation of the change or object.
+type ListenerFunc func(instance interface{})
+
+func (f ListenerFunc) OnUpdate(instance interface{}) {
+	f(instance)
+}
+
+type Watcher struct {
+	// Listeners for changes and their lock.
+	listenerLock sync.RWMutex
+	listeners    []Listener
+}
+
+// Register a set of listeners that support the Listener interface and
+// notify them on changes.
+func NewWatcher() *Watcher {
+	return &Watcher{}
+}
+
+// Register Listener to receive updates of changes.
+func (m *Watcher) Add(listener Listener) {
+	m.listenerLock.Lock()
+	defer m.listenerLock.Unlock()
+	m.listeners = append(m.listeners, listener)
+}
+
+// Notify all listeners
+func (m *Watcher) Notify(instance interface{}) {
+	m.listenerLock.RLock()
+	listeners := m.listeners
+	m.listenerLock.RUnlock()
+	for _, listener := range listeners {
+		listener.OnUpdate(instance)
+	}
+}

pkg/util/config/config_test.go

@@ -0,0 +1,120 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package config
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestConfigurationChannels(t *testing.T) {
+	mux := NewMux(nil)
+	channelOne := mux.Channel("one")
+	if channelOne != mux.Channel("one") {
+		t.Error("Didn't get the same muxuration channel back with the same name")
+	}
+	channelTwo := mux.Channel("two")
+	if channelOne == channelTwo {
+		t.Error("Got back the same muxuration channel for different names")
+	}
+}
+
+type MergeMock struct {
+	source string
+	update interface{}
+	t      *testing.T
+}
+
+func (m MergeMock) Merge(source string, update interface{}) error {
+	if m.source != source {
+		m.t.Errorf("Expected %s, Got %s", m.source, source)
+	}
+	if !reflect.DeepEqual(m.update, update) {
+		m.t.Errorf("Expected %s, Got %s", m.update, update)
+	}
+	return nil
+}
+
+func TestMergeInvoked(t *testing.T) {
+	merger := MergeMock{"one", "test", t}
+	mux := NewMux(&merger)
+	mux.Channel("one") <- "test"
+}
+
+func TestMergeFuncInvoked(t *testing.T) {
+	ch := make(chan bool)
+	mux := NewMux(MergeFunc(func(source string, update interface{}) error {
+		if source != "one" {
+			t.Errorf("Expected %s, Got %s", "one", source)
+		}
+		if update.(string) != "test" {
+			t.Errorf("Expected %s, Got %s", "test", update)
+		}
+		ch <- true
+		return nil
+	}))
+	mux.Channel("one") <- "test"
+	<-ch
+}
+
+func TestSimultaneousMerge(t *testing.T) {
+	ch := make(chan bool, 2)
+	mux := NewMux(MergeFunc(func(source string, update interface{}) error {
+		switch source {
+		case "one":
+			if update.(string) != "test" {
+				t.Errorf("Expected %s, Got %s", "test", update)
+			}
+		case "two":
+			if update.(string) != "test2" {
+				t.Errorf("Expected %s, Got %s", "test2", update)
+			}
+		default:
+			t.Errorf("Unexpected source, Got %s", update)
+		}
+		ch <- true
+		return nil
+	}))
+	source := mux.Channel("one")
+	source2 := mux.Channel("two")
+	source <- "test"
+	source2 <- "test2"
+	<-ch
+	<-ch
+}
+
+func TestWatcher(t *testing.T) {
+	watch := NewWatcher()
+	watch.Notify(struct{}{})
+
+	ch := make(chan bool, 2)
+	watch.Add(ListenerFunc(func(object interface{}) {
+		if object != "test" {
+			t.Errorf("Expected %s, Got %s", "test", object)
+		}
+		ch <- true
+	}))
+	watch.Add(ListenerFunc(func(object interface{}) {
+		if object != "test" {
+			t.Errorf("Expected %s, Got %s", "test", object)
+		}
+		ch <- true
+	}))
+	watch.Notify("test")
+	<-ch
+	<-ch
+}

pkg/util/config/doc.go

@@ -0,0 +1,20 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package config provides utility objects for decoupling sources of configuration and the
+// actual configuration state. Consumers must implement the Merger interface to unify
+// the sources of change into an object.
+package config