Promtail: Add ready endoint to loki-push-api server (#8552)

When trying to expose loki_push_api service (in our case using GKE ingress), we need a health check target endpoint that would return a 200 response code. This PR contains a simple addition for a HTTP handler that handles the /ready path, along with the necessary tests.

Fixes #8551

Co-authored-by: Christian Haudum <[email protected]>

Author: Yasmine92

clients/pkg/promtail/targets/lokipush/pushtarget.go

@@ -89,6 +89,7 @@ func (t *PushTarget) run() error {
 	t.server = srv
 	t.server.HTTP.Path("/loki/api/v1/push").Methods("POST").Handler(http.HandlerFunc(t.handleLoki))
 	t.server.HTTP.Path("/promtail/api/v1/raw").Methods("POST").Handler(http.HandlerFunc(t.handlePlaintext))
+	t.server.HTTP.Path("/ready").Methods("GET").Handler(http.HandlerFunc(t.ready))
 
 	go func() {
 		err := srv.Run()
@@ -234,3 +235,11 @@ func (t *PushTarget) Stop() error {
 	t.handler.Stop()
 	return nil
 }
+
+// ready function serves the ready endpoint
+func (t *PushTarget) ready(w http.ResponseWriter, r *http.Request) {
+	resp := "ready"
+	if _, err := w.Write([]byte(resp)); err != nil {
+		level.Error(t.logger).Log("msg", "failed to respond to ready endoint", "err", err)
+	}
+}

clients/pkg/promtail/targets/lokipush/pushtarget_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"flag"
 	"fmt"
+	"io"
 	"net"
 	"net/http"
 	"os"
@@ -200,3 +201,67 @@ func TestPlaintextPushTarget(t *testing.T) {
 	_ = pt.Stop()
 
 }
+
+func TestReady(t *testing.T) {
+	w := log.NewSyncWriter(os.Stderr)
+	logger := log.NewLogfmtLogger(w)
+
+	//Create PushTarget
+	eh := fake.New(func() {})
+	defer eh.Stop()
+
+	// Get a randomly available port by open and closing a TCP socket
+	addr, err := net.ResolveTCPAddr("tcp", localhost+":0")
+	require.NoError(t, err)
+	l, err := net.ListenTCP("tcp", addr)
+	require.NoError(t, err)
+	port := l.Addr().(*net.TCPAddr).Port
+	err = l.Close()
+	require.NoError(t, err)
+
+	// Adjust some of the defaults
+	defaults := server.Config{}
+	defaults.RegisterFlags(flag.NewFlagSet("empty", flag.ContinueOnError))
+	defaults.HTTPListenAddress = localhost
+	defaults.HTTPListenPort = port
+	defaults.GRPCListenAddress = localhost
+	defaults.GRPCListenPort = 0 // Not testing GRPC, a random port will be assigned
+
+	config := &scrapeconfig.PushTargetConfig{
+		Server: defaults,
+		Labels: model.LabelSet{
+			"pushserver": "pushserver2",
+			"keepme":     "label",
+		},
+		KeepTimestamp: true,
+	}
+
+	pt, err := NewPushTarget(logger, eh, []*relabel.Config{}, "job3", config)
+	require.NoError(t, err)
+
+	url := fmt.Sprintf("http://%s:%d/ready", localhost, port)
+	response, err := http.Get(url)
+	if err != nil {
+		require.NoError(t, err)
+	}
+	body, err := io.ReadAll(response.Body)
+	if err != nil {
+		require.NoError(t, err)
+	}
+	responseCode := fmt.Sprint(response.StatusCode)
+	responseBody := string(body)
+
+	fmt.Println(responseBody)
+	wantedResponse := "ready"
+	if responseBody != wantedResponse {
+		t.Errorf("got the response %q, want %q", responseBody, wantedResponse)
+	}
+	wantedCode := "200"
+	if responseCode != wantedCode {
+		t.Errorf("Got the response code %q, want %q", responseCode, wantedCode)
+	}
+
+	t.Cleanup(func() {
+		_ = pt.Stop()
+	})
+}

docs/sources/clients/promtail/configuration.md

@@ -877,6 +877,8 @@ Note the `server` configuration is the same as [server](#server).
 Promtail also exposes a second endpoint on `/promtail/api/v1/raw` which expects newline-delimited log lines.
 This can be used to send NDJSON or plaintext logs.
 
+The readiness of the loki_push_api server can be checked using the endpoint `/ready`.
+
 ```yaml
 # The push server configuration options
 [server: <server_config>]