Don't throw away valid configuration updates

pkg/server/configurationwatcher.go

@@ -143,8 +143,6 @@ func (c *ConfigurationWatcher) loadMessage(configMsg dynamic.Message) {
 }
 
 func (c *ConfigurationWatcher) preLoadConfiguration(configMsg dynamic.Message) {
-	currentConfigurations := c.currentConfigurations.Get().(dynamic.Configurations)
-
 	logger := log.WithoutContext().WithField(log.ProviderName, configMsg.ProviderName)
 	if log.GetLevel() == logrus.DebugLevel {
 		copyConf := configMsg.Configuration.DeepCopy()
@@ -172,11 +170,6 @@ func (c *ConfigurationWatcher) preLoadConfiguration(configMsg dynamic.Message) {
 		return
 	}
 
-	if reflect.DeepEqual(currentConfigurations[configMsg.ProviderName], configMsg.Configuration) {
-		logger.Infof("Skipping same configuration for provider %s", configMsg.ProviderName)
-		return
-	}
-
 	providerConfigUpdateCh, ok := c.providerConfigUpdateMap[configMsg.ProviderName]
 	if !ok {
 		providerConfigUpdateCh = make(chan dynamic.Message)
@@ -211,11 +204,18 @@ func (c *ConfigurationWatcher) throttleProviderConfigReload(ctx context.Context,
 		}
 	})
 
+	var previousConfig dynamic.Message
 	for {
 		select {
 		case <-ctx.Done():
 			return
 		case nextConfig := <-in:
+			if reflect.DeepEqual(previousConfig, nextConfig) {
+				logger := log.WithoutContext().WithField(log.ProviderName, nextConfig.ProviderName)
+				logger.Info("Skipping same configuration")
+				continue
+			}
+			previousConfig = nextConfig
 			ring.In() <- nextConfig
 		}
 	}

pkg/server/configurationwatcher_test.go

@@ -175,6 +175,66 @@ func TestListenProvidersSkipsSameConfigurationForProvider(t *testing.T) {
 	time.Sleep(100 * time.Millisecond)
 }
 
+func TestListenProvidersDoesNotSkipFlappingConfiguration(t *testing.T) {
+	routinesPool := safe.NewPool(context.Background())
+
+	configuration := &dynamic.Configuration{
+		HTTP: th.BuildConfiguration(
+			th.WithRouters(th.WithRouter("foo")),
+			th.WithLoadBalancerServices(th.WithService("bar")),
+		),
+	}
+
+	transientConfiguration := &dynamic.Configuration{
+		HTTP: th.BuildConfiguration(
+			th.WithRouters(th.WithRouter("bad")),
+			th.WithLoadBalancerServices(th.WithService("bad")),
+		),
+	}
+
+	pvd := &mockProvider{
+		wait: 5 * time.Millisecond, // The last message needs to be received before the second has been fully processed
+		messages: []dynamic.Message{
+			{ProviderName: "mock", Configuration: configuration},
+			{ProviderName: "mock", Configuration: transientConfiguration},
+			{ProviderName: "mock", Configuration: configuration},
+		},
+	}
+
+	watcher := NewConfigurationWatcher(routinesPool, pvd, 15*time.Millisecond)
+
+	var lastConfig dynamic.Configuration
+	watcher.AddListener(func(conf dynamic.Configuration) {
+		lastConfig = conf
+	})
+
+	watcher.Start()
+	defer watcher.Stop()
+
+	// give some time so that the configuration can be processed
+	time.Sleep(40 * time.Millisecond)
+
+	expected := dynamic.Configuration{
+		HTTP: th.BuildConfiguration(
+			th.WithRouters(th.WithRouter("foo@mock")),
+			th.WithLoadBalancerServices(th.WithService("bar@mock")),
+			th.WithMiddlewares(),
+		),
+		TCP: &dynamic.TCPConfiguration{
+			Routers:  map[string]*dynamic.TCPRouter{},
+			Services: map[string]*dynamic.TCPService{},
+		},
+		TLS: &dynamic.TLSConfiguration{
+			Options: map[string]tls.Options{
+				"default": {},
+			},
+			Stores: map[string]tls.Store{},
+		},
+	}
+
+	assert.Equal(t, expected, lastConfig)
+}
+
 func TestListenProvidersPublishesConfigForEachProvider(t *testing.T) {
 	routinesPool := safe.NewPool(context.Background())