Add collector example

example/metric/README.md

@@ -22,7 +22,11 @@ Next, set this project ID to the environment variable `GOOGLE_PROJECT_ID` using
 export GOOGLE_PROJECT_ID=$(gcloud config get-value project)
 ```
 
-Once you ensure the API is enabled, then build the example application and run the executable.
+Once you ensure the API is enabled, then build the example application and run the executable. There are two separate examples showcasing the following - 
+1. Exporting metrics via the SDK.
+2. Exporting metrics via the OpenTelemetry Collector.
+
+Change the current directory to the example you wish to run - either to `sdk` directory or `collector` directory and then run the example using following commands:
 
 ```
 $ go build -o metrics
@@ -36,6 +40,8 @@ $ ./metrics
 
 To ensure you have enough data to create interesting charts for the Counter and Observer metrics generated by the example, keep the application running for at least five minutes.
 
+*Note: For running the collector example, you need to have a locally running OpenTelemetry Collector, configured using the provided [sample config](./collector/sample-collector-config.yaml). Instructions for running OpenTelemetry Collector on your system can be found [here](https://opentelemetry.io/docs/collector/getting-started/#local).*
+
 ## Create dashboard
 
 https://console.cloud.google.com/monitoring/dashboards?project=<your-project-id>
@@ -54,4 +60,6 @@ This script creates a dashboard titled "OpenTelemetry exporter example/metric".
 
 You should be able to view line charts like below once you create the dashboard.
 
+*Note: This script is configured to create dashboard which displays the metrics generated via the `sdk` example.*
+
 <img width="1200" alt="2 charts in dashboard" src="images/charts.png?raw=true"/>

example/metric/collector/example.go

@@ -0,0 +1,168 @@
+// Copyright 2023 Google LLC
+//
+// 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 main
+
+import (
+	"context"
+	"log"
+	"math/rand"
+	"sync"
+	"time"
+
+	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp"
+
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/metric"
+	sdkmetric "go.opentelemetry.io/otel/sdk/metric"
+)
+
+type observedFloat struct {
+	mu sync.RWMutex
+	f  float64
+}
+
+func (of *observedFloat) set(v float64) {
+	of.mu.Lock()
+	defer of.mu.Unlock()
+	of.f = v
+}
+
+func (of *observedFloat) get() float64 {
+	of.mu.RLock()
+	defer of.mu.RUnlock()
+	return of.f
+}
+
+func newObservedFloat(v float64) *observedFloat {
+	return &observedFloat{
+		f: v,
+	}
+}
+
+type observedInt struct {
+	mu sync.RWMutex
+	i  int64
+}
+
+func (oi *observedInt) set(v int64) {
+	oi.mu.Lock()
+	defer oi.mu.Unlock()
+	oi.i = v
+}
+
+func (oi *observedInt) get() int64 {
+	oi.mu.RLock()
+	defer oi.mu.RUnlock()
+	return oi.i
+}
+
+func newObservedInt(v int64) *observedInt {
+	return &observedInt{
+		i: v,
+	}
+}
+
+// Export OTLP metrtics using the otlpmetrichttp exporter.
+// This example is used to demostrate how to use the collector approach to export metrics to Google Cloud.
+func main() {
+
+	ctx := context.Background()
+	exp, err := otlpmetrichttp.New(ctx, otlpmetrichttp.WithInsecure())
+	if err != nil {
+		panic(err)
+	}
+
+	// initialize a MeterProvider with that periodically exports to the otlp exporter.
+	provider := sdkmetric.NewMeterProvider(
+		sdkmetric.WithReader(sdkmetric.NewPeriodicReader(exp)),
+	)
+	defer func() {
+		if err = provider.Shutdown(ctx); err != nil {
+			log.Fatalf("failed to shutdown meter provider: %v", err)
+		}
+	}()
+
+	// Create a meter with which we will record metrics for our package.
+	meter := provider.Meter("github.com/GoogleCloudPlatform/opentelemetry-operations-go/example/collector/metric")
+
+	// Register counter value
+	counter, err := meter.Int64Counter("counter-a-collector")
+	if err != nil {
+		log.Fatalf("Failed to create counter: %v", err)
+	}
+	clabels := []attribute.KeyValue{attribute.Key("key").String("value")}
+	counter.Add(ctx, 100, metric.WithAttributes(clabels...))
+
+	histogram, err := meter.Float64Histogram("histogram-b-collector")
+	if err != nil {
+		log.Fatalf("Failed to create histogram: %v", err)
+	}
+
+	// Register observer value
+	olabels := []attribute.KeyValue{
+		attribute.String("foo", "Tokyo"),
+		attribute.String("bar", "Sushi"),
+	}
+	of := newObservedFloat(12.34)
+
+	gaugeObserver, err := meter.Float64ObservableGauge("observer-a-collector")
+	if err != nil {
+		log.Fatalf("failed to initialize instrument: %v", err)
+	}
+	_, err = meter.RegisterCallback(func(ctx context.Context, o metric.Observer) error {
+		v := of.get()
+		o.ObserveFloat64(gaugeObserver, v, metric.WithAttributes(olabels...))
+		return nil
+	}, gaugeObserver)
+	if err != nil {
+		log.Fatalf("failed to register callback: %v", err)
+	}
+
+	oi := newObservedInt(3)
+	// Export boolean as a custom type (Boolean types are not supported in OTLP)
+	gaugeObserverBool, err := meter.Int64ObservableGauge("observer-boolean-collector", metric.WithUnit("{gcp.BOOL}"))
+	if err != nil {
+		log.Fatalf("failed to initialize instrument: %v", err)
+	}
+	_, err = meter.RegisterCallback(func(ctx context.Context, o metric.Observer) error {
+		v := oi.get()
+		o.ObserveInt64(gaugeObserverBool, v, metric.WithAttributes(clabels...))
+		return nil
+	}, gaugeObserverBool)
+	if err != nil {
+		log.Fatalf("failed to register callback: %v", err)
+	}
+
+	// Add measurement once an every 10 second.
+	timer := time.NewTicker(10 * time.Second)
+	rng := rand.New(rand.NewSource(time.Now().UnixNano()))
+	for range timer.C {
+		r := rng.Int63n(100)
+		cv := 100 + r
+		counter.Add(ctx, cv, metric.WithAttributes(clabels...))
+
+		r2 := rng.Int63n(100)
+		hv := float64(r2) / 20.0
+		histogram.Record(ctx, hv, metric.WithAttributes(clabels...))
+		ovf := 12.34 + hv
+		of.set(ovf)
+
+		r3 := rng.Int63n(2) // 0 or 1
+		ovi := int64(r3)
+		oi.set(ovi)
+
+		log.Printf("Most recent data: counter %v, observer-float %v; observer-int %v; histogram %v", cv, ovf, ovi, hv)
+	}
+}

example/metric/collector/go.mod

@@ -0,0 +1,29 @@
+module github.com/GoogleCloudPlatform/opentelemetry-operations-go/example/metric/collector
+
+go 1.21
+
+require (
+	go.opentelemetry.io/otel v1.16.0
+	go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp v0.39.0
+	go.opentelemetry.io/otel/metric v1.16.0
+	go.opentelemetry.io/otel/sdk/metric v0.39.0
+)
+
+require (
+	github.com/cenkalti/backoff/v4 v4.2.1 // indirect
+	github.com/go-logr/logr v1.2.4 // indirect
+	github.com/go-logr/stdr v1.2.2 // indirect
+	github.com/golang/protobuf v1.5.3 // indirect
+	github.com/grpc-ecosystem/grpc-gateway/v2 v2.7.0 // indirect
+	go.opentelemetry.io/otel/exporters/otlp/internal/retry v1.16.0 // indirect
+	go.opentelemetry.io/otel/exporters/otlp/otlpmetric v0.39.0 // indirect
+	go.opentelemetry.io/otel/sdk v1.16.0 // indirect
+	go.opentelemetry.io/otel/trace v1.16.0 // indirect
+	go.opentelemetry.io/proto/otlp v0.19.0 // indirect
+	golang.org/x/net v0.8.0 // indirect
+	golang.org/x/sys v0.8.0 // indirect
+	golang.org/x/text v0.8.0 // indirect
+	google.golang.org/genproto v0.0.0-20230306155012-7f2fa6fef1f4 // indirect
+	google.golang.org/grpc v1.55.0 // indirect
+	google.golang.org/protobuf v1.30.0 // indirect
+)