Don't trace /healthz (#844)

Kubernetes users end up having tons of /healthz traces
which is costly and no-value.

Disable known health endpoint tracing until we have a better solution.

Author: rakyll

plugin/ochttp/client.go

@@ -57,6 +57,9 @@ type Transport struct {
 // RoundTrip implements http.RoundTripper, delegating to Base and recording stats and traces for the request.
 func (t *Transport) RoundTrip(req *http.Request) (*http.Response, error) {
 	rt := t.base()
+	if isHealthEndpoint(req.URL.Path) {
+		return rt.RoundTrip(req)
+	}
 	// TODO: remove excessive nesting of http.RoundTrippers here.
 	format := t.Propagation
 	if format == nil {

plugin/ochttp/server.go

@@ -82,6 +82,9 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 }
 
 func (h *Handler) startTrace(w http.ResponseWriter, r *http.Request) (*http.Request, func()) {
+	if isHealthEndpoint(r.URL.Path) {
+		return r, func() {}
+	}
 	var name string
 	if h.FormatSpanName == nil {
 		name = spanNameFromURL(r)

plugin/ochttp/server_test.go

@@ -551,3 +551,44 @@ func TestHandlerImplementsHTTPCloseNotify(t *testing.T) {
 		t.Errorf("HTTP2Log got\n\t%q\nwant\n\t%q", g, w)
 	}
 }
+
+func TestIgnoreHealthz(t *testing.T) {
+	var spans int
+
+	ts := httptest.NewServer(&Handler{
+		Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			span := trace.FromContext(r.Context())
+			if span != nil {
+				spans++
+			}
+			fmt.Fprint(w, "ok")
+		}),
+		StartOptions: trace.StartOptions{
+			Sampler: trace.AlwaysSample(),
+		},
+	})
+	defer ts.Close()
+
+	client := &http.Client{}
+
+	for _, path := range []string{"/healthz", "/_ah/health"} {
+		resp, err := client.Get(ts.URL + path)
+		if err != nil {
+			t.Fatalf("Cannot GET %q: %v", path, err)
+		}
+
+		b, err := ioutil.ReadAll(resp.Body)
+		if err != nil {
+			t.Fatalf("Cannot read body for %q: %v", path, err)
+		}
+
+		if got, want := string(b), "ok"; got != want {
+			t.Fatalf("Body for %q = %q; want %q", path, got, want)
+		}
+		resp.Body.Close()
+	}
+
+	if spans > 0 {
+		t.Errorf("Got %v spans; want no spans", spans)
+	}
+}

plugin/ochttp/trace.go

@@ -197,3 +197,15 @@ var codeToStr = map[int32]string{
 	trace.StatusCodeDataLoss:           `"DATA_LOSS"`,
 	trace.StatusCodeUnauthenticated:    `"UNAUTHENTICATED"`,
 }
+
+func isHealthEndpoint(path string) bool {
+	// Health checking is pretty frequent and
+	// traces collected for health endpoints
+	// can be extremely noisy and expensive.
+	// Disable canonical health checking endpoints
+	// like /healthz and /_ah/health for now.
+	if path == "/healthz" || path == "/_ah/health" {
+		return true
+	}
+	return false
+}