Record and emit the timestamp that the last connection was establishe…

…d to ACS

ecs-agent/acs/session/session.go

@@ -64,6 +64,7 @@ const (
 // The Session.Start() method can be used to start processing messages from ACS.
 type Session interface {
 	Start(context.Context) error
+	GetLastConnectedTime() time.Time
 }
 
 // session encapsulates all arguments needed to connect to ACS and to handle messages received by ACS.
@@ -97,6 +98,7 @@ type session struct {
 	disconnectTimeout              time.Duration
 	disconnectJitter               time.Duration
 	inactiveInstanceReconnectDelay time.Duration
+	lastConnectedTime              time.Time
 }
 
 // NewSession creates a new Session.
@@ -155,6 +157,7 @@ func NewSession(containerInstanceARN string,
 		disconnectTimeout:              wsclient.DisconnectTimeout,
 		disconnectJitter:               wsclient.DisconnectJitterMax,
 		inactiveInstanceReconnectDelay: inactiveInstanceReconnectDelay,
+		lastConnectedTime:              time.Time{},
 	}
 }
 
@@ -245,6 +248,9 @@ func (s *session) startSessionOnce(ctx context.Context) error {
 	}
 	defer disconnectTimer.Stop()
 
+	// Record the timestamp of the last connection to ACS.
+	s.lastConnectedTime = time.Now()
+
 	// Connection to ACS was successful. Moving forward, rely on ACS to send credentials to Agent at its own cadence
 	// and make sure Agent does not force ACS to send credentials for any subsequent reconnects to ACS.
 	logger.Info("Connected to ACS endpoint")
@@ -425,3 +431,8 @@ func formatDockerVersion(dockerVersionValue string) string {
 	}
 	return dockerVersionValue
 }
+
+// GetLastConnectedTime returns the timestamp that the last connection was established to ACS.
+func (s *session) GetLastConnectedTime() time.Time {
+	return s.lastConnectedTime
+}

ecs-agent/acs/session/session_test.go

@@ -1286,6 +1286,98 @@ func TestSessionCallsAddUpdateRequestHandlers(t *testing.T) {
 	assert.True(t, addUpdateRequestHandlersCalled)
 }
 
+// TestGetLastConnectedTime tests that the Session's 'lastConnectedTime' field  is updated correctly for successive
+// invocations of startSessionOnce. Also tests that the Session's GetLastConnectedTime() API call works as expected.
+func TestGetLastConnectedTime(t *testing.T) {
+	ctrl := gomock.NewController(t)
+	defer ctrl.Finish()
+
+	const numInvocations = 10
+	discoverEndpointClient := mock_api.NewMockECSDiscoverEndpointSDK(ctrl)
+	discoverEndpointClient.EXPECT().DiscoverPollEndpoint(gomock.Any()).Return(acsURL, nil).AnyTimes()
+	ctx, cancel := context.WithCancel(context.Background())
+
+	mockWsClient := mock_wsclient.NewMockClientServer(ctrl)
+	mockClientFactory := mock_wsclient.NewMockClientFactory(ctrl)
+	mockClientFactory.EXPECT().
+		New(gomock.Any(), gomock.Any(), gomock.Any(), gomock.Any(), gomock.Any()).
+		Return(mockWsClient).AnyTimes()
+	mockWsClient.EXPECT().SetAnyRequestHandler(gomock.Any()).AnyTimes()
+	mockWsClient.EXPECT().AddRequestHandler(gomock.Any()).AnyTimes()
+	mockWsClient.EXPECT().WriteCloseMessage().AnyTimes()
+	mockWsClient.EXPECT().Close().Return(nil).AnyTimes()
+	mockWsClient.EXPECT().Serve(gomock.Any()).Return(io.EOF).AnyTimes()
+
+	acsSession := NewSession(testconst.ContainerInstanceARN,
+		testconst.ClusterARN,
+		discoverEndpointClient,
+		nil,
+		noopFunc,
+		mockClientFactory,
+		metricsfactory.NewNopEntryFactory(),
+		agentVersion,
+		agentGitShortHash,
+		dockerVersion,
+		nil,
+		nil,
+		nil,
+		nil,
+		nil,
+		nil,
+		nil,
+		nil,
+		nil,
+		nil,
+		nil,
+		nil,
+	)
+	acsSession.(*session).heartbeatTimeout = 20 * time.Millisecond
+	acsSession.(*session).heartbeatJitter = 10 * time.Millisecond
+	acsSession.(*session).disconnectTimeout = 30 * time.Millisecond
+	acsSession.(*session).disconnectJitter = 10 * time.Millisecond
+	gomock.InOrder(
+		// When the websocket client connects to ACS for the first time, 'sendCredentials' should be set to true.
+		mockWsClient.EXPECT().Connect(gomock.Any(), gomock.Any(), gomock.Any()).Do(func(interface{},
+			interface{}, interface{}) {
+			assert.Equal(t, true, acsSession.(*session).sendCredentials)
+		}).Return(time.NewTimer(wsclient.DisconnectTimeout), nil),
+		// For all subsequent connections to ACS, 'sendCredentials' should be set to false.
+		mockWsClient.EXPECT().Connect(gomock.Any(), gomock.Any(), gomock.Any()).Do(func(interface{},
+			interface{}, interface{}) {
+			assert.Equal(t, false, acsSession.(*session).sendCredentials)
+		}).Return(time.NewTimer(wsclient.DisconnectTimeout), nil).Times(numInvocations-1),
+	)
+
+	// The Session's lastConnectedTime field was initialized with time.Time{}, which is the default zero value for time.Time.
+	// At this point, since the Session has not connected to ACS yet, the Session's lastConnectedTime should still be zero.
+	assert.True(t, acsSession.GetLastConnectedTime().IsZero())
+
+	go func() {
+		for i := 0; i < numInvocations; i++ {
+			// Record the current time.
+			currentTime := time.Now()
+			// Invoke startSessionOnce() to connect to ACS.
+			acsSession.(*session).startSessionOnce(ctx)
+			// Get the timestamp recorded in Session's lastConnectedTime field.
+			acsSessionActualConnectedTime := acsSession.GetLastConnectedTime()
+			// Compare the two timestamps.
+			// Since the connection was started right after the first timestamp was recorded, the two timestamps should
+			// be very close. Allow an 1 ms to account for jitters.
+			assert.WithinDuration(t, currentTime, acsSessionActualConnectedTime, 1*time.Millisecond)
+			// Sleep for 2 ms before proceeding to the next test iteration, so that if the Session's lastConnectedTime
+			// field is not correctly updated, it would be caught since the allowed delta is 1 ms.
+			time.Sleep(2 * time.Millisecond)
+		}
+		cancel()
+	}()
+
+	// Wait for context to be canceled.
+	select {
+	case <-ctx.Done():
+		cancel()
+	}
+}
+
 func startFakeACSServer(closeWS <-chan bool) (*httptest.Server, chan<- string, <-chan string, <-chan error, error) {
 	serverChan := make(chan string, 1)
 	requestsChan := make(chan string, 1)