Add Knative network probe endpoints

This adds a header `k-network-probe`, to which the Knative networking elements
respond without forwarding the requests.  They also identify themselves in their
response, so that we know what component is handling the probe.

This is related to: knative#2856, knative#2849, knative#3239

cmd/activator/main.go

@@ -246,19 +246,21 @@ func main() {
 	cr := activatorhandler.NewConcurrencyReporter(podName, reqChan, time.NewTicker(time.Second).C, statChan)
 	go cr.Run(stopCh)
 
-	ah := &activatorhandler.FilteringHandler{
-		NextHandler: activatorhandler.NewRequestEventHandler(reqChan,
-			&activatorhandler.EnforceMaxContentLengthHandler{
-				MaxContentLengthBytes: maxUploadBytes,
-				NextHandler: &activatorhandler.ActivationHandler{
-					Activator: a,
-					Transport: rt,
-					Logger:    logger,
-					Reporter:  reporter,
-					Throttler: throttler,
+	ah := &activatorhandler.ProbeHandler{
+		NextHandler: &activatorhandler.FilteringHandler{
+			NextHandler: activatorhandler.NewRequestEventHandler(reqChan,
+				&activatorhandler.EnforceMaxContentLengthHandler{
+					MaxContentLengthBytes: maxUploadBytes,
+					NextHandler: &activatorhandler.ActivationHandler{
+						Activator: a,
+						Transport: rt,
+						Logger:    logger,
+						Reporter:  reporter,
+						Throttler: throttler,
+					},
 				},
-			},
-		),
+			),
+		},
 	}
 
 	// Watch the logging config map and dynamically update logging levels.

cmd/queue/main.go

@@ -38,6 +38,7 @@ import (
 	"github.com/knative/serving/pkg/autoscaler"
 	"github.com/knative/serving/pkg/http/h2c"
 	"github.com/knative/serving/pkg/logging"
+	"github.com/knative/serving/pkg/network"
 	"github.com/knative/serving/pkg/queue"
 	"github.com/knative/serving/pkg/queue/health"
 	"github.com/knative/serving/pkg/utils"
@@ -158,7 +159,11 @@ func proxyForRequest(req *http.Request) *httputil.ReverseProxy {
 	return httpProxy
 }
 
-func isProbe(r *http.Request) bool {
+func isKnativeProbe(r *http.Request) bool {
+	return r.Header.Get(network.ProbeHeaderName) != ""
+}
+
+func isKubeletProbe(r *http.Request) bool {
 	// Since K8s 1.8, prober requests have
 	//   User-Agent = "kube-probe/{major-version}.{minor-version}".
 	return strings.HasPrefix(r.Header.Get("User-Agent"), "kube-probe/")
@@ -167,7 +172,13 @@ func isProbe(r *http.Request) bool {
 func handler(w http.ResponseWriter, r *http.Request) {
 	proxy := proxyForRequest(r)
 
-	if isProbe(r) {
+	if isKnativeProbe(r) {
+		// Respond with the name of the component handling the request.
+		w.Write([]byte("queue"))
+		return
+	}
+
+	if isKubeletProbe(r) {
 		// Do not count health checks for concurrency metrics
 		proxy.ServeHTTP(w, r)
 		return

pkg/activator/handler/filtering_handler_test.go

@@ -31,20 +31,17 @@ func TestFilteringHandler(t *testing.T) {
 		headers:        http.Header{},
 		passed:         true,
 		expectedStatus: http.StatusOK,
-	},
-		{
-			label:          "filter a request containing retry header",
-			headers:        mapToHeader(map[string]string{activator.RequestCountHTTPHeader: "4"}),
-			passed:         false,
-			expectedStatus: http.StatusServiceUnavailable,
-		},
-		{
-			label:          "forward a request containing empty retry header",
-			headers:        mapToHeader(map[string]string{activator.RequestCountHTTPHeader: ""}),
-			passed:         true,
-			expectedStatus: http.StatusOK,
-		},
-	}
+	}, {
+		label:          "filter a request containing retry header",
+		headers:        mapToHeader(map[string]string{activator.RequestCountHTTPHeader: "4"}),
+		passed:         false,
+		expectedStatus: http.StatusServiceUnavailable,
+	}, {
+		label:          "forward a request containing empty retry header",
+		headers:        mapToHeader(map[string]string{activator.RequestCountHTTPHeader: ""}),
+		passed:         true,
+		expectedStatus: http.StatusOK,
+	}}
 
 	for _, e := range examples {
 		t.Run(e.label, func(t *testing.T) {

pkg/activator/handler/probe_handler.go

@@ -0,0 +1,36 @@
+/*
+Copyright 2019 The Knative Authors
+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 handler
+
+import (
+	"net/http"
+
+	"github.com/knative/serving/pkg/network"
+)
+
+// ProbeHandler handles responding to Knative internal network probes.
+type ProbeHandler struct {
+	NextHandler http.Handler
+}
+
+func (h *ProbeHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	// If this header is set the request was sent by a Knative component
+	// probing the network, respond with a 200 and our component name.
+	if r.Header.Get(network.ProbeHeaderName) != "" {
+		w.Write([]byte("activator"))
+		return
+	}
+
+	h.NextHandler.ServeHTTP(w, r)
+}

pkg/activator/handler/probe_handler_test.go

@@ -0,0 +1,74 @@
+/*
+Copyright 2019 The Knative Authors
+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 handler
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/knative/serving/pkg/network"
+)
+
+func TestProbeHandler(t *testing.T) {
+	examples := []struct {
+		label          string
+		headers        http.Header
+		passed         bool
+		expectedStatus int
+	}{{
+		label:          "forward a normal request",
+		headers:        http.Header{},
+		passed:         true,
+		expectedStatus: http.StatusOK,
+	}, {
+		label:          "filter a request containing probe header",
+		headers:        mapToHeader(map[string]string{network.ProbeHeaderName: "not-empty"}),
+		passed:         false,
+		expectedStatus: http.StatusOK,
+	}, {
+		label:          "forward a request containing empty retry header",
+		headers:        mapToHeader(map[string]string{network.ProbeHeaderName: ""}),
+		passed:         true,
+		expectedStatus: http.StatusOK,
+	}}
+
+	for _, e := range examples {
+		t.Run(e.label, func(t *testing.T) {
+			wasPassed := false
+			baseHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				wasPassed = true
+				w.WriteHeader(http.StatusOK)
+			})
+			handler := ProbeHandler{NextHandler: baseHandler}
+
+			resp := httptest.NewRecorder()
+			req := httptest.NewRequest("POST", "http://example.com", nil)
+			req.Header = e.headers
+
+			handler.ServeHTTP(resp, req)
+
+			if wasPassed != e.passed {
+				if !e.passed {
+					t.Error("Request got passed to the next handler unexpectedly")
+				} else {
+					t.Error("Request was not passed to the next handler as expected")
+				}
+			}
+
+			if resp.Code != e.expectedStatus {
+				t.Errorf("Unexpected response status. Want %d, got %d", e.expectedStatus, resp.Code)
+			}
+		})
+	}
+}

pkg/network/network.go

@@ -24,6 +24,12 @@ import (
 )
 
 const (
+	// ProbeHeaderName is the name of a header that can be added to
+	// requests to probe the knative networking layer.  Requests
+	// with this header will not be passed to the user container or
+	// included in request metrics.
+	ProbeHeaderName = "k-network-probe"
+
 	// ConfigName is the name of the configmap containing all
 	// customizations for networking features.
 	ConfigName = "config-network"