Updating documentation around OTEL (#6519)

Updating documentation around the opentelemetry endpoint for metrics and
the "How to use OpenTelemetry metrics with VictoriaMetrics" guide so
that it shows not only how to directly write but also how to write to
the otel collector and view metrics in vmui.

---------

Signed-off-by: Zakhar Bessarab <z.bessarab@victoriametrics.com>
Co-authored-by: Zakhar Bessarab <z.bessarab@victoriametrics.com>

README.md

@@ -1624,6 +1624,25 @@ Set HTTP request header `Content-Encoding: gzip` when sending gzip-compressed da
 VictoriaMetrics stores the ingested OpenTelemetry [raw samples](https://docs.victoriametrics.com/keyconcepts/#raw-samples) as is without any transformations.
 Pass `-opentelemetry.usePrometheusNaming` command-line flag to VictoriaMetrics for automatic conversion of metric names and labels into Prometheus-compatible format.
 
+Using the following exporter configuration in the opentelemetry collector will allow you to send metrics into VictoriaMetrics:
+
+```yaml
+exporters:
+  otlphttp/victoriametrics:
+    compression: gzip
+    encoding: proto
+    endpoint: http://<collector/vmagent>.<namespace>.svc.cluster.local:<port>/opentelemetry
+```
+Remember to add the exporter to the desired service pipeline in order to activate the exporter.
+```yaml
+service:
+  pipelines:
+    metrics:
+      exporters:
+        - otlphttp/victoriametrics
+      receivers:
+        - otlp
+```
 See [How to use OpenTelemetry metrics with VictoriaMetrics](https://docs.victoriametrics.com/guides/getting-started-with-opentelemetry/).
 
 ## JSON line format

docs/README.md

@@ -1627,6 +1627,25 @@ Set HTTP request header `Content-Encoding: gzip` when sending gzip-compressed da
 VictoriaMetrics stores the ingested OpenTelemetry [raw samples](https://docs.victoriametrics.com/keyconcepts/#raw-samples) as is without any transformations.
 Pass `-opentelemetry.usePrometheusNaming` command-line flag to VictoriaMetrics for automatic conversion of metric names and labels into Prometheus-compatible format.
 
+Using the following exporter configuration in the opentelemetry collector will allow you to send metrics into VictoriaMetrics:
+
+```yaml
+exporters:
+  otlphttp/victoriametrics:
+    compression: gzip
+    encoding: proto
+    endpoint: http://<collector/vmagent>.<namespace>.svc.cluster.local:<port>/opentelemetry
+```
+Remember to add the exporter to the desired service pipeline in order to activate the exporter.
+```yaml
+service:
+  pipelines:
+    metrics:
+      exporters:
+        - otlphttp/victoriametrics
+      receivers:
+        - otlp
+```
 See [How to use OpenTelemetry metrics with VictoriaMetrics](https://docs.victoriametrics.com/guides/getting-started-with-opentelemetry/).
 
 ## JSON line format

docs/Single-server-VictoriaMetrics.md

@@ -1635,6 +1635,25 @@ Set HTTP request header `Content-Encoding: gzip` when sending gzip-compressed da
 VictoriaMetrics stores the ingested OpenTelemetry [raw samples](https://docs.victoriametrics.com/keyconcepts/#raw-samples) as is without any transformations.
 Pass `-opentelemetry.usePrometheusNaming` command-line flag to VictoriaMetrics for automatic conversion of metric names and labels into Prometheus-compatible format.
 
+Using the following exporter configuration in the opentelemetry collector will allow you to send metrics into VictoriaMetrics:
+
+```yaml
+exporters:
+  otlphttp/victoriametrics:
+    compression: gzip
+    encoding: proto
+    endpoint: http://<collector/vmagent>.<namespace>.svc.cluster.local:<port>/opentelemetry
+```
+Remember to add the exporter to the desired service pipeline in order to activate the exporter.
+```yaml
+service:
+  pipelines:
+    metrics:
+      exporters:
+        - otlphttp/victoriametrics
+      receivers:
+        - otlp
+```
 See [How to use OpenTelemetry metrics with VictoriaMetrics](https://docs.victoriametrics.com/guides/getting-started-with-opentelemetry/).
 
 ## JSON line format

docs/guides/getting-started-with-opentelemetry-app.go-collector.example

@@ -0,0 +1,223 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"io"
+	"log"
+	"math/rand"
+	"net"
+	"net/http"
+	"os"
+	"os/signal"
+	"strconv"
+	"time"
+
+	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp"
+	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp"
+	"go.opentelemetry.io/otel/propagation"
+	otelmetric "go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/sdk/metric"
+	"go.opentelemetry.io/otel/sdk/resource"
+	"go.opentelemetry.io/otel/sdk/trace"
+	semconv "go.opentelemetry.io/otel/semconv/v1.25.0"
+)
+
+func main() {
+	if err := run(); err != nil {
+		log.Fatalln(err)
+	}
+}
+
+func run() (err error) {
+	// Handle SIGINT (CTRL+C) gracefully.
+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt)
+	defer stop()
+
+	// Set up OpenTelemetry.
+	otelShutdown, err := setupOTelSDK(ctx)
+	if err != nil {
+		return
+	}
+	// Handle shutdown properly so nothing leaks.
+	defer func() {
+		err = errors.Join(err, otelShutdown(context.Background()))
+	}()
+
+	// Start HTTP server.
+	srv := &http.Server{
+		Addr:         ":8080",
+		BaseContext:  func(_ net.Listener) context.Context { return ctx },
+		ReadTimeout:  time.Second,
+		WriteTimeout: 10 * time.Second,
+		Handler:      newHTTPHandler(),
+	}
+	srvErr := make(chan error, 1)
+	go func() {
+		srvErr <- srv.ListenAndServe()
+	}()
+
+	// Wait for interruption.
+	select {
+	case err = <-srvErr:
+		// Error when starting HTTP server.
+		return
+	case <-ctx.Done():
+		// Wait for first CTRL+C.
+		// Stop receiving signal notifications as soon as possible.
+		stop()
+	}
+
+	// When Shutdown is called, ListenAndServe immediately returns ErrServerClosed.
+	err = srv.Shutdown(context.Background())
+	return
+}
+
+func newHTTPHandler() http.Handler {
+	mux := http.NewServeMux()
+
+	// handleFunc is a replacement for mux.HandleFunc
+	// which enriches the handler's HTTP instrumentation with the pattern as the http.route.
+	handleFunc := func(pattern string, handlerFunc func(http.ResponseWriter, *http.Request)) {
+		// Configure the "http.route" for the HTTP instrumentation.
+		handler := otelhttp.WithRouteTag(pattern, http.HandlerFunc(handlerFunc))
+		mux.Handle(pattern, handler)
+	}
+
+	// Register handlers.
+	handleFunc("/rolldice", rolldice)
+
+	// Add HTTP instrumentation for the whole server.
+	handler := otelhttp.NewHandler(mux, "/")
+	return handler
+}
+
+var (
+	tracer  = otel.Tracer("rolldice")
+	meter   = otel.Meter("rolldice")
+	rollCnt otelmetric.Int64Counter
+)
+
+func init() {
+	var err error
+	rollCnt, err = meter.Int64Counter("dice.rolls",
+	otelmetric.WithDescription("The number of rolls by roll value"),
+	otelmetric.WithUnit("{roll}"))
+	if err != nil {
+		panic(err)
+	}
+}
+
+func rolldice(w http.ResponseWriter, r *http.Request) {
+	ctx, span := tracer.Start(r.Context(), "roll")
+	defer span.End()
+
+	roll := 1 + rand.Intn(6)
+
+	rollValueAttr := attribute.Int("roll.value", roll)
+	span.SetAttributes(rollValueAttr)
+	rollCnt.Add(ctx, 1, otelmetric.WithAttributes(rollValueAttr))
+
+	resp := strconv.Itoa(roll) + "\n"
+	if _, err := io.WriteString(w, resp); err != nil {
+		log.Printf("Write failed: %v\n", err)
+	}
+}
+
+// setupOTelSDK bootstraps the OpenTelemetry pipeline.
+// If it does not return an error, make sure to call shutdown for proper cleanup.
+func setupOTelSDK(ctx context.Context) (shutdown func(context.Context) error, err error) {
+	var shutdownFuncs []func(context.Context) error
+
+	// shutdown calls cleanup functions registered via shutdownFuncs.
+	// The errors from the calls are joined.
+	// Each registered cleanup will be invoked once.
+	shutdown = func(ctx context.Context) error {
+		var err error
+		for _, fn := range shutdownFuncs {
+			err = errors.Join(err, fn(ctx))
+		}
+		shutdownFuncs = nil
+		return err
+	}
+
+	// handleErr calls shutdown for cleanup and makes sure that all errors are returned.
+	handleErr := func(inErr error) {
+		err = errors.Join(inErr, shutdown(ctx))
+	}
+
+	// Set up propagator.
+	prop := newPropagator()
+	otel.SetTextMapPropagator(prop)
+
+	// Set up trace provider.
+	tracerProvider, err := newTraceProvider(ctx)
+	if err != nil {
+		handleErr(err)
+		return
+	}
+	shutdownFuncs = append(shutdownFuncs, tracerProvider.Shutdown)
+	otel.SetTracerProvider(tracerProvider)
+
+	// Set up meter provider.
+	meterProvider, err := newMeterProvider(ctx)
+	if err != nil {
+		handleErr(err)
+		return
+	}
+	shutdownFuncs = append(shutdownFuncs, meterProvider.Shutdown)
+	otel.SetMeterProvider(meterProvider)
+
+	return
+}
+
+func newPropagator() propagation.TextMapPropagator {
+	return propagation.NewCompositeTextMapPropagator(
+		propagation.TraceContext{},
+		propagation.Baggage{},
+	)
+}
+
+func newTraceProvider(ctx context.Context) (*trace.TracerProvider, error) {
+	traceExporter, err := otlptracehttp.New(ctx, otlptracehttp.WithInsecure(), otlptracehttp.WithEndpoint("localhost:4318"))
+	if err != nil {
+		return nil, err
+	}
+
+	traceProvider := trace.NewTracerProvider(
+		trace.WithBatcher(traceExporter,
+			// Default is 5s. Set to 1s for demonstrative purposes.
+			trace.WithBatchTimeout(time.Second)),
+	)
+	return traceProvider, nil
+}
+
+func newMeterProvider(ctx context.Context) (*metric.MeterProvider, error) {
+	metricExporter, err := otlpmetrichttp.New(ctx, otlpmetrichttp.WithInsecure(), otlpmetrichttp.WithEndpoint("localhost:4318"))
+	if err != nil {
+		return nil, err
+	}
+	//metricExporter, err := stdoutmetric.New()
+	//if err != nil {
+	//	return nil, err
+	//}
+	res, err := resource.Merge(resource.Default(),
+		resource.NewWithAttributes(semconv.SchemaURL,
+			semconv.ServiceName("dice-roller"),
+			semconv.ServiceVersion("0.1.0"),
+		))
+	if err != nil {
+		return nil, err
+	}
+	meterProvider := metric.NewMeterProvider(
+		metric.WithResource(res),
+		metric.WithReader(metric.NewPeriodicReader(metricExporter,
+			// Default is 1m. Set to 3s for demonstrative purposes.
+			metric.WithInterval(3*time.Second))),
+	)
+
+	return meterProvider, nil
+}

docs/guides/getting-started-with-opentelemetry.md

@@ -55,23 +55,37 @@ helm repo update
 
 # add values
 cat << EOF > values.yaml
+mode: deployment
+image:
+  repository: "otel/opentelemetry-collector-contrib"
 presets:
   clusterMetrics:
     enabled: true
 config:
+  receivers:
+    otlp:
+      protocols:
+        grpc:
+          endpoint: 0.0.0.0:4317
+        http:
+          endpoint: 0.0.0.0:4318
   exporters:
-   prometheusremotewrite:
-     endpoint: "http://victoria-metrics-victoria-metrics-single-server.default.svc.cluster.local:8428/api/v1/write" 
+   otlphttp/victoriametrics:
+     compression: gzip
+     encoding: proto
+     endpoint: http://victoria-metrics-victoria-metrics-single-server.default.svc.cluster.local:8428/opentelemetry
+     tls:
+        insecure: true
   service:
-      pipelines:
-        metrics:
-          receivers: [otlp]
-          processors: []
-          exporters: [prometheusremotewrite] 
+    pipelines:
+      metrics:
+        receivers: [otlp]
+        processors: []
+        exporters: [otlphttp/victoriametrics]
 EOF
 
 # install helm chart
-helm upgrade -i otl-collector open-telemetry/opentelemetry-collector --set mode=deployment -f values.yaml
+helm upgrade -i otl-collector open-telemetry/opentelemetry-collector -f values.yaml
 
 # check if pod is healthy
 kubectl get pod
@@ -79,13 +93,78 @@ NAME                                                     READY   STATUS    RESTA
 otl-collector-opentelemetry-collector-7467bbb559-2pq2n   1/1     Running   0          23m
 
 # forward port to local machine to verify metrics are ingested
-kubectl port-forward victoria-metrics-victoria-metrics-single-server-0 8428
+kubectl port-forward service/victoria-metrics-victoria-metrics-single-server 8428
 
 # check metric `k8s_container_ready` via browser http://localhost:8428/vmui/#/?g0.expr=k8s_container_ready
+
+# forward port to local machine to setup opentelemetry-collector locally
+kubectl port-forward otl-collector-opentelemetry-collector 4318
+
 ```
 
 The full version of possible configuration options could be found in [OpenTelemetry docs](https://opentelemetry.io/docs/collector/configuration/).
 
+## Sending to VictoriaMetrics via OpenTelemetry
+Metrics could be sent to VictoriaMetrics via OpenTelemetry instrumentation libraries. You can use any compatible OpenTelemetry instrumentation [clients](https://opentelemetry.io/docs/languages/).
+In our example, we'll create a WEB server in [Golang](https://go.dev/) and instrument it with metrics.
+
+### Building the Go application instrumented with metrics
+Copy the go file from [here](/guides/getting-started-with-opentelemetry-app.go-collector.example). This will give you a basic implementation of a dice roll WEB server with the urls for opentelemetry-collector pointing to localhost:4318. 
+In the same directory run the following command to create the `go.mod` file:
+```sh
+go mod init vm/otel
+```
+
+For demo purposes, we'll add the following dependencies to `go.mod` file:
+```go
+
+require (
+	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.52.0
+	go.opentelemetry.io/otel v1.27.0
+	go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp v1.27.0
+	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.27.0
+	go.opentelemetry.io/otel/metric v1.27.0
+	go.opentelemetry.io/otel/sdk v1.27.0
+	go.opentelemetry.io/otel/sdk/metric v1.27.0
+)
+
+require (
+	github.com/cenkalti/backoff/v4 v4.3.0 // indirect
+	github.com/felixge/httpsnoop v1.0.4 // indirect
+	github.com/go-logr/logr v1.4.1 // indirectdice.rolls
+	github.com/go-logr/stdr v1.2.2 // indirect
+	github.com/grpc-ecosystem/grpc-gateway/v2 v2.20.0 // indirect
+	go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.27.0 // indirect
+	go.opentelemetry.io/otel/trace v1.27.0 // indirect
+	go.opentelemetry.io/proto/otlp v1.2.0 // indirect
+	golang.org/x/net v0.25.0 // indirect
+	golang.org/x/sys v0.20.0 // indirect
+	golang.org/x/text v0.15.0 // indirect
+	google.golang.org/genproto/googleapis/api v0.0.0-20240520151616-dc85e6b867a5 // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20240515191416-fc5f0ca64291 // indirect
+	google.golang.org/grpc v1.64.0 // indirect
+	google.golang.org/protobuf v1.34.1 // indirect
+)
+```
+
+Once you have these in your `go.mod` file, you can run the following command to download the dependencies:
+```sh
+go mod tidy
+```
+
+Now you can run the application:
+```sh
+go run .
+```
+
+### Test metrics ingestion
+By default, the application will be available at `localhost:8080`. You can start sending requests to /rolldice endpoint to generate metrics. The following command will send 20 requests to the /rolldice endpoint:
+```sh
+for i in `seq 1 20`; do curl http://localhost:8080/rolldice; done
+```
+
+After a few seconds you should start to see metrics sent over to the vmui interface by visiting `http://localhost:8428/vmui/#/?g0.expr=dice.rolls` in your browser or by querying the metric `dice.rolls` in the vmui interface.
+<img src="/guides/vmui-dice-roll.webp">
 ## Direct metrics push
 
 Metrics could be ingested into VictoriaMetrics directly with HTTP requests. You can use any compatible OpenTelemetry