Return custom header when request was returned from a cold start

interceptor/forward_wait_func.go

@@ -11,7 +11,7 @@ import (
 
 // forwardWaitFunc is a function that waits for a condition
 // before proceeding to serve the request.
-type forwardWaitFunc func(context.Context, string, string) error
+type forwardWaitFunc func(context.Context, string, string) (int, error)
 
 func deploymentCanServe(depl appsv1.Deployment) bool {
 	return depl.Status.ReadyReplicas > 0
@@ -21,7 +21,7 @@ func newDeployReplicasForwardWaitFunc(
 	lggr logr.Logger,
 	deployCache k8s.DeploymentCache,
 ) forwardWaitFunc {
-	return func(ctx context.Context, deployNS, deployName string) error {
+	return func(ctx context.Context, deployNS, deployName string) (int, error) {
 		// get a watcher & its result channel before querying the
 		// deployment cache, to ensure we don't miss events
 		watcher := deployCache.Watch(deployNS, deployName)
@@ -31,7 +31,7 @@ func newDeployReplicasForwardWaitFunc(
 		deployment, err := deployCache.Get(deployNS, deployName)
 		if err != nil {
 			// if we didn't get the initial deployment state, bail out
-			return fmt.Errorf(
+			return 0, fmt.Errorf(
 				"error getting state for deployment %s/%s (%s)",
 				deployNS,
 				deployName,
@@ -40,7 +40,7 @@ func newDeployReplicasForwardWaitFunc(
 		}
 		// if there is 1 or more replica, we're done waiting
 		if deploymentCanServe(deployment) {
-			return nil
+			return int(deployment.Status.ReadyReplicas), nil
 		}
 
 		for {
@@ -51,14 +51,13 @@ func newDeployReplicasForwardWaitFunc(
 					lggr.Info(
 						"Didn't get a deployment back in event",
 					)
-				}
-				if deploymentCanServe(*deployment) {
-					return nil
+				} else if deploymentCanServe(*deployment) {
+					return 0, nil
 				}
 			case <-ctx.Done():
 				// otherwise, if the context is marked done before
 				// we're done waiting, fail.
-				return fmt.Errorf(
+				return 0, fmt.Errorf(
 					"context marked done while waiting for deployment %s to reach > 0 replicas (%w)",
 					deployName,
 					ctx.Err(),

interceptor/forward_wait_func_test.go

@@ -43,7 +43,8 @@ func TestForwardWaitFuncOneReplica(t *testing.T) {
 	)
 
 	group.Go(func() error {
-		return waitFunc(ctx, ns, deployName)
+		_, err := waitFunc(ctx, ns, deployName)
+		return err
 	})
 	r.NoError(group.Wait(), "wait function failed, but it shouldn't have")
 }
@@ -76,7 +77,7 @@ func TestForwardWaitFuncNoReplicas(t *testing.T) {
 		cache,
 	)
 
-	err := waitFunc(ctx, ns, deployName)
+	_, err := waitFunc(ctx, ns, deployName)
 	r.Error(err)
 }
 
@@ -120,6 +121,7 @@ func TestWaitFuncWaitsUntilReplicas(t *testing.T) {
 		watcher.Action(watch.Modified, modifiedDeployment)
 		close(replicasIncreasedCh)
 	}()
-	r.NoError(waitFunc(ctx, ns, deployName))
+	_, err := waitFunc(ctx, ns, deployName)
+	r.NoError(err)
 	done()
 }

interceptor/main_test.go

@@ -66,9 +66,9 @@ func TestRunProxyServerCountMiddleware(t *testing.T) {
 	)
 	timeouts := &config.Timeouts{}
 	waiterCh := make(chan struct{})
-	waitFunc := func(ctx context.Context, ns, name string) error {
+	waitFunc := func(ctx context.Context, ns, name string) (int, error) {
 		<-waiterCh
-		return nil
+		return 1, nil
 	}
 	g.Go(func() error {
 		return runProxyServer(
@@ -106,6 +106,9 @@ func TestRunProxyServerCountMiddleware(t *testing.T) {
 				resp.StatusCode,
 			)
 		}
+		if resp.Header.Get("X-KEDA-HTTP-Cold-Start") != "false" {
+			return fmt.Errorf("expected X-KEDA-HTTP-Cold-Start false, but got %s", resp.Header.Get("X-KEDA-HTTP-Cold-Start"))
+		}
 		return nil
 	})
 	time.Sleep(100 * time.Millisecond)

interceptor/proxy_handlers.go

@@ -74,11 +74,12 @@ func newForwardingHandler(
 
 		waitFuncCtx, done := context.WithTimeout(r.Context(), fwdCfg.waitTimeout)
 		defer done()
-		if err := waitFunc(
+		replicas, err := waitFunc(
 			waitFuncCtx,
 			routingTarget.Namespace,
 			routingTarget.Deployment,
-		); err != nil {
+		)
+		if err != nil {
 			lggr.Error(err, "wait function failed, not forwarding request")
 			w.WriteHeader(502)
 			w.Write([]byte(fmt.Sprintf("error on backend (%s)", err)))
@@ -91,6 +92,11 @@ func newForwardingHandler(
 			w.Write([]byte("error getting backend service URL"))
 			return
 		}
+		isColdStart := "false"
+		if replicas == 0 {
+			isColdStart = "true"
+		}
+		w.Header().Add("X-KEDA-HTTP-Cold-Start", isColdStart)
 		forwardRequest(w, r, roundTripper, targetSvcURL)
 	})
 }

interceptor/proxy_handlers_test.go

@@ -45,8 +45,8 @@ func TestImmediatelySuccessfulProxy(t *testing.T) {
 
 	timeouts := defaultTimeouts()
 	dialCtxFunc := retryDialContextFunc(timeouts, timeouts.DefaultBackoff())
-	waitFunc := func(context.Context, string, string) error {
-		return nil
+	waitFunc := func(context.Context, string, string) (int, error) {
+		return 1, nil
 	}
 	hdl := newForwardingHandler(
 		logr.Discard(),
@@ -68,6 +68,7 @@ func TestImmediatelySuccessfulProxy(t *testing.T) {
 
 	hdl.ServeHTTP(res, req)
 
+	r.Equal("false", res.Header().Get("X-KEDA-HTTP-Cold-Start"), "expected X-KEDA-HTTP-Cold-Start false")
 	r.Equal(200, res.Code, "expected response code 200")
 	r.Equal("test response", res.Body.String())
 }
@@ -85,8 +86,8 @@ func TestWaitFailedConnection(t *testing.T) {
 		timeouts,
 		backoff,
 	)
-	waitFunc := func(context.Context, string, string) error {
-		return nil
+	waitFunc := func(context.Context, string, string) (int, error) {
+		return 1, nil
 	}
 	routingTable := routing.NewTable()
 	routingTable.AddTarget(host, routing.NewTarget(
@@ -117,6 +118,7 @@ func TestWaitFailedConnection(t *testing.T) {
 
 	hdl.ServeHTTP(res, req)
 
+	r.Equal("false", res.Header().Get("X-KEDA-HTTP-Cold-Start"), "expected X-KEDA-HTTP-Cold-Start false")
 	r.Equal(502, res.Code, "response code was unexpected")
 }
 
@@ -166,13 +168,19 @@ func TestTimesOutOnWaitFunc(t *testing.T) {
 
 	t.Logf("elapsed time was %s", elapsed)
 	// serving should take at least timeouts.DeploymentReplicas, but no more than
-	// timeouts.DeploymentReplicas*2
-	// elapsed time should be more than the deployment replicas wait time
-	// but not an amount that is much greater than that
+	// timeouts.DeploymentReplicas*4
 	r.GreaterOrEqual(elapsed, timeouts.DeploymentReplicas)
 	r.LessOrEqual(elapsed, timeouts.DeploymentReplicas*4)
 	r.Equal(502, res.Code, "response code was unexpected")
 
+	// we will always return the X-KEDA-HTTP-Cold-Start header
+	// when we are able to forward the
+	// request to the backend but not if we have failed due
+	// to a timeout from a waitFunc or earlier in the pipeline,
+	// for example, if we cannot reach the Kubernetes control
+	// plane.
+	r.Equal("", res.Header().Get("X-KEDA-HTTP-Cold-Start"), "expected X-KEDA-HTTP-Cold-Start to be empty")
+
 	// waitFunc should have been called, even though it timed out
 	waitFuncCalled := false
 	select {
@@ -277,8 +285,8 @@ func TestWaitHeaderTimeout(t *testing.T) {
 
 	timeouts := defaultTimeouts()
 	dialCtxFunc := retryDialContextFunc(timeouts, timeouts.DefaultBackoff())
-	waitFunc := func(context.Context, string, string) error {
-		return nil
+	waitFunc := func(context.Context, string, string) (int, error) {
+		return 1, nil
 	}
 	routingTable := routing.NewTable()
 	target := routing.NewTarget(
@@ -309,6 +317,7 @@ func TestWaitHeaderTimeout(t *testing.T) {
 
 	hdl.ServeHTTP(res, req)
 
+	r.Equal("false", res.Header().Get("X-KEDA-HTTP-Cold-Start"), "expected X-KEDA-HTTP-Cold-Start false")
 	r.Equal(502, res.Code, "response code was unexpected")
 	close(originHdlCh)
 }
@@ -346,19 +355,19 @@ func waitForSignal(sig <-chan struct{}, waitDur time.Duration) error {
 // is called, or the context that is passed to it is done (e.g. cancelled, timed out,
 // etc...). in the former case, the returned func itself returns nil. in the latter,
 // it returns ctx.Err()
-func notifyingFunc() (func(context.Context, string, string) error, <-chan struct{}, func()) {
+func notifyingFunc() (forwardWaitFunc, <-chan struct{}, func()) {
 	calledCh := make(chan struct{})
 	finishCh := make(chan struct{})
 	finishFunc := func() {
 		close(finishCh)
 	}
-	return func(ctx context.Context, _, _ string) error {
+	return func(ctx context.Context, _, _ string) (int, error) {
 		close(calledCh)
 		select {
 		case <-finishCh:
-			return nil
+			return 0, nil
 		case <-ctx.Done():
-			return fmt.Errorf("TEST FUNCTION CONTEXT ERROR: %w", ctx.Err())
+			return 0, fmt.Errorf("TEST FUNCTION CONTEXT ERROR: %w", ctx.Err())
 		}
 	}, calledCh, finishFunc
 }