Add HTTP endpoint /api/echo to query-frontend (#714)

The echo endpoint can be used by Grafana to test Tempo whether is reachable. #624

CHANGELOG.md

@@ -10,6 +10,7 @@
   This change requires a specific rollout process to prevent dropped spans. First, rollout everything except distributors. After all ingesters have updated
   you can then rollout distributors to the latest version. This is due to changes in the communication between ingesters <-> distributors.
 * [ENHANCEMENT] Allow setting the bloom filter shard size with support dynamic shard count.[#644](https://github.com/grafana/tempo/pull/644)
+* [ENHANCEMENT] Add a new endpoint `/api/echo` to test the query frontend is reachable. [#714](https://github.com/grafana/tempo/pull/714)
 * [CHANGE] Fix Query Frontend grpc settings to avoid noisy error log. [#690](https://github.com/grafana/tempo/pull/690)
 * [CHANGE] GCS SDK update v1.12.0 => v.15.0, ReadAllWithEstimate used in GCS/S3 backends. [#693](https://github.com/grafana/tempo/pull/693)
 

cmd/tempo/app/modules.go

@@ -3,6 +3,7 @@ package app
 import (
 	"fmt"
 	"net/http"
+	"path"
 
 	"github.com/cortexproject/cortex/pkg/cortex"
 	cortex_frontend "github.com/cortexproject/cortex/pkg/frontend"
@@ -45,6 +46,11 @@ const (
 	All           string = "all"
 )
 
+const (
+	apiPathTraces string = "/api/traces/{traceID}"
+	apiPathEcho   string = "/api/echo"
+)
+
 func (t *App) initServer() (services.Service, error) {
 	t.cfg.Server.MetricsNamespace = metricsNamespace
 	t.cfg.Server.ExcludeRequestInLog = true
@@ -151,7 +157,7 @@ func (t *App) initQuerier() (services.Service, error) {
 		t.httpAuthMiddleware,
 	).Wrap(http.HandlerFunc(t.querier.TraceByIDHandler))
 
-	t.server.HTTP.Handle("/querier"+queryEndpoint(&t.cfg), tracesHandler)
+	t.server.HTTP.Handle(path.Join("/querier", addHTTPAPIPrefix(&t.cfg, apiPathTraces)), tracesHandler)
 	return t.querier, t.querier.CreateAndRegisterWorker(t.server.HTTPServer.Handler)
 }
 
@@ -183,7 +189,9 @@ func (t *App) initQueryFrontend() (services.Service, error) {
 	// register grpc server for queriers to connect to
 	cortex_frontend_v1pb.RegisterFrontendServer(t.server.GRPC, t.frontend)
 	// http query endpoint
-	t.server.HTTP.Handle(queryEndpoint(&t.cfg), tracesHandler)
+	t.server.HTTP.Handle(addHTTPAPIPrefix(&t.cfg, apiPathTraces), tracesHandler)
+
+	t.server.HTTP.Handle(addHTTPAPIPrefix(&t.cfg, apiPathEcho), echoHandler())
 
 	return t.frontend, nil
 }
@@ -271,6 +279,12 @@ func (t *App) setupModuleManager() error {
 	return nil
 }
 
-func queryEndpoint(cfg *Config) string {
-	return cfg.HTTPAPIPrefix + "/api/traces/{traceID}"
+func addHTTPAPIPrefix(cfg *Config, apiPath string) string {
+	return path.Join(cfg.HTTPAPIPrefix, apiPath)
+}
+
+func echoHandler() http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		http.Error(w, "echo", http.StatusOK)
+	}
 }

integration/e2e/e2e_test.go

@@ -58,6 +58,9 @@ func TestAllInOne(t *testing.T) {
 
 	hexID := fmt.Sprintf("%016x%016x", batch.Spans[0].TraceIdHigh, batch.Spans[0].TraceIdLow)
 
+	// test echo
+	assertEcho(t, "http://"+tempo.Endpoint(3100)+"/api/echo")
+
 	// ensure trace is created in ingester (trace_idle_time has passed)
 	require.NoError(t, tempo.WaitSumMetrics(cortex_e2e.Equals(1), "tempo_ingester_traces_created_total"))
 
@@ -117,6 +120,9 @@ func TestAzuriteAllInOne(t *testing.T) {
 
 	hexID := fmt.Sprintf("%016x%016x", batch.Spans[0].TraceIdHigh, batch.Spans[0].TraceIdLow)
 
+	// test echo
+	assertEcho(t, "http://"+tempo.Endpoint(3100)+"/api/echo")
+
 	// ensure trace is created in ingester (trace_idle_time has passed)
 	require.NoError(t, tempo.WaitSumMetrics(cortex_e2e.Equals(1), "tempo_ingester_traces_created_total"))
 
@@ -186,6 +192,9 @@ func TestMicroservices(t *testing.T) {
 
 	hexID := fmt.Sprintf("%016x%016x", batch.Spans[0].TraceIdHigh, batch.Spans[0].TraceIdLow)
 
+	// test echo
+	assertEcho(t, "http://"+tempoQueryFrontend.Endpoint(3100)+"/api/echo")
+
 	// ensure trace is created in ingester (trace_idle_time has passed)
 	require.NoError(t, tempoIngester1.WaitSumMetrics(cortex_e2e.Equals(1), "tempo_ingester_traces_created_total"))
 	require.NoError(t, tempoIngester2.WaitSumMetrics(cortex_e2e.Equals(1), "tempo_ingester_traces_created_total"))
@@ -265,6 +274,13 @@ func makeThriftBatchWithSpanCount(n int) *thrift.Batch {
 	return &thrift.Batch{Spans: spans}
 }
 
+func assertEcho(t *testing.T, url string) {
+	res, err := cortex_e2e.GetRequest(url)
+	require.NoError(t, err)
+	require.Equal(t, 200, res.StatusCode)
+	defer res.Body.Close()
+}
+
 //nolint:unparam
 func queryAndAssertTrace(t *testing.T, url string, expectedName string, expectedBatches int) {
 	res, err := cortex_e2e.GetRequest(url)