Observability Series ตอนที่ 4 — เก็บ Metrics ด้วย OpenTelemetry + OTLP Metric (gRPC)

[Fiber App]
   |
[OTLP Metric gRPC Exporter]
   |
[OTel Collector]
   |
[Prometheus]
   |
[Grafana]

project-root/
│
├── cmd/
│   └── main.go               # จุดเริ่มโปรแกรม, bootstrap Fiber, DI, middleware
│
├── internal/
│   ├── handler/
│   │   └── user_handler.go   # HTTP Handlers (Fiber routes)
│   │
│   ├── service/
│   │   └── user_service.go   # Business Logic Layer
│   │
│   └── repository/
│       └── user_repo.go      # Data Access Layer
│
├── pkg/
│   ├── ctxkey/
│   │   └── ctxkey.go         # Shared Lib: เก็บ context key
│   │
│   ├── logger/
│   │   └── logger.go         # Shared Lib: Logger setup (Zap)
│   │
│   ├── middleware/           # Shared Lib: Middleware
│   │    └── observability_middleware.go
│   │
│   └── observability/
│       └── observability.go  # Shared Lib: Trace + Metric
│
├── go.mod
└── go.sum

go get go.opentelemetry.io/otel
go get go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc
go get go.opentelemetry.io/otel/sdk/metric
go get go.opentelemetry.io/otel/metric
go get go.opentelemetry.io/contrib/instrumentation/runtime

package observability

import (
	"context"
	"log"
	"time"

	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc"
	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc"

	sdkmetric "go.opentelemetry.io/otel/sdk/metric"
	"go.opentelemetry.io/otel/sdk/resource"
	sdktrace "go.opentelemetry.io/otel/sdk/trace"
	semconv "go.opentelemetry.io/otel/semconv/v1.21.0"
)

type OTel struct {
	TracerProvider *sdktrace.TracerProvider
	MeterProvider  *sdkmetric.MeterProvider // เพิ่ม metric
}

func (c *OTel) Shutdown(ctx context.Context) {
	ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
	defer cancel()

	if err := c.TracerProvider.Shutdown(ctx); err != nil {
		log.Println("failed to shutdown tracer:", err)
	}

	if err := c.MeterProvider.Shutdown(ctx); err != nil { // เพิ่ม metric
		log.Println("failed to shutdown meter:", err)
	}
}

func NewOTel(ctx context.Context, collectorAddr, serviceName string) (*OTel, error) {
	// ----- Resource -----
	res, err := resource.New(ctx,
		resource.WithAttributes(
			semconv.ServiceName(serviceName),
		),
	)
	if err != nil {
		return nil, err
	}

	// ----- Tracer -----
	traceExp, err := otlptracegrpc.New(ctx,
		otlptracegrpc.WithEndpoint(collectorAddr),
		otlptracegrpc.WithInsecure(),
	)
	if err != nil {
		return nil, err
	}

	tp := sdktrace.NewTracerProvider(
		sdktrace.WithBatcher(traceExp),
		sdktrace.WithResource(res),
	)
	otel.SetTracerProvider(tp)

	// ----- Meter -----
	metricExp, err := otlpmetricgrpc.New(ctx,
		otlpmetricgrpc.WithEndpoint(collectorAddr),
		otlpmetricgrpc.WithInsecure(),
	)
	if err != nil {
		return nil, err
	}

	mp := sdkmetric.NewMeterProvider(
		sdkmetric.WithReader(
			sdkmetric.NewPeriodicReader(metricExp),
		),
		sdkmetric.WithResource(res),
	)
	otel.SetMeterProvider(mp)

	return &OTel{
		TracerProvider: tp,
		MeterProvider:  mp,
	}, nil
}

package middleware

import (
	"context"
	"demo/pkg/ctxkey"
	"fmt"
	"runtime/debug"
	"strings"
	"time"

	"github.com/gofiber/fiber/v2"
	"github.com/google/uuid"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/metric"
	"go.opentelemetry.io/otel/trace"
	"go.uber.org/zap"
)

func NewObservabilityMiddleware(
	baseLogger *zap.Logger,
	tracer trace.Tracer,
	meter metric.Meter,
) fiber.Handler {

	// ----- OTel Instruments -----
	requestCounter, _ := meter.Int64Counter("http_requests_total")
	requestDuration, _ := meter.Float64Histogram("http_request_duration_ms")
	inflightCounter, _ := meter.Int64UpDownCounter("http_requests_inflight")
	requestSize, _ := meter.Float64Histogram("http_request_size_bytes")
	responseSize, _ := meter.Float64Histogram("http_response_size_bytes")
	errorCounter, _ := meter.Int64Counter("http_requests_error_total")

	// Skip Paths ที่ไม่ต้องการ trace
	skipPaths := map[string]bool{
		"/health":  true,
		"/metrics": true,
	}
	// กรณีมีการ serve SPA
	staticPrefixes := []string{"/static", "/assets", "/public", "/favicon", "/robots.txt"}

	return func(c *fiber.Ctx) error {
		start := time.Now()
		method := c.Method()
		path := c.Path()

		// ตรวจสอบ path ที่เรียกมา
		skip := skipPaths[path]
		for _, prefix := range staticPrefixes {
			if strings.HasPrefix(path, prefix) {
				skip = true
				break
			}
		}

		var (
			ctx     context.Context
			span    trace.Span
			traceID string
		)

		if skip {
			ctx = c.Context()
		} else {
			ctx, span = tracer.Start(c.Context(), "HTTP "+c.Method()+" "+path)
			defer span.End()
			traceID = span.SpanContext().TraceID().String()
		}

		requestID := c.Get("X-Request-ID")
		if requestID == "" {
			requestID = uuid.New().String()
		}

		// Bind Request ID ลง Response Header
		c.Set("X-Request-ID", requestID)

		// สร้าง child logger
		reqLogger := baseLogger.With(
			zap.String("trace_id", traceID), // เพิ่ม trace_id เพื่อเชื่อมโยง log กับ trace
			zap.String("request_id", requestID),
		)

		// สร้าง Context ใหม่ที่มี logger
		ctx = context.WithValue(ctx, ctxkey.Logger{}, reqLogger)
		// แทน Context เดิม
		c.SetUserContext(ctx)

		// ----- Record Inflight -----
		if !skip {
			inflightCounter.Add(ctx, 1)
		}

		err := c.Next()

		duration := time.Since(start).Milliseconds()
		status := c.Response().StatusCode()

		if !skip {
			labels := []attribute.KeyValue{
				attribute.String("method", method),
				attribute.String("path", path),
				attribute.Int("status", status),
			}

			requestCounter.Add(ctx, 1, metric.WithAttributes(labels...))
			requestDuration.Record(ctx, float64(duration), metric.WithAttributes(labels...))
			inflightCounter.Add(ctx, -1)

			// Request Size (Header Content-Length)
			if reqSize := c.Request().Header.ContentLength(); reqSize > 0 {
				requestSize.Record(ctx, float64(reqSize), metric.WithAttributes(labels...))
			}

			// Response Size (Body Length)
			if resSize := len(c.Response().Body()); resSize > 0 {
				responseSize.Record(ctx, float64(resSize), metric.WithAttributes(labels...))
			}

			if status >= 400 {
				errorCounter.Add(ctx, 1, metric.WithAttributes(labels...))
			}
		}

		// log unhandle error
		if err != nil {
			reqLogger.Error("an error occurred",
				zap.Any("error", err),
				zap.ByteString("stack", debug.Stack()),
			)
		}

		msg := fmt.Sprintf("%d - %s %s", status, method, path)
		reqLogger.Info(msg,
			zap.Int("status", status),
			zap.Int64("duration_ms", duration),
		)

		return err
	}
}

package main

import (
	"context"
	"os"
	"time"

	"go.opentelemetry.io/contrib/instrumentation/runtime"

	"github.com/gofiber/fiber/v2"
	"github.com/gofiber/fiber/v2/middleware/cors"
	"github.com/gofiber/fiber/v2/middleware/recover"

	"demo/internal/handler"
	"demo/internal/repository"
	"demo/internal/service"
	"demo/pkg/logger"
	"demo/pkg/middleware"
	"demo/pkg/observability"
)

func main() {
	// Init Logger
	logger.Init()

	// Init Observability via Opentelmetry
	otel, err := observability.NewOTel(
		context.Background(),
		os.Getenv("OTEL_EXPORTER_OTLP_ENDPOINT"),
		"demo-app")
	if err != nil {
		logger.Default().Fatal(err.Error())
	}
	defer otel.Shutdown(context.Background())

	// เก็บ Process Metrics: สร้าง Runtime Instrument → ผูกกับ MeterProvider
	runtime.Start(
		runtime.WithMinimumReadMemStatsInterval(time.Second * 10),
	)

	// Init Fiber
	app := fiber.New()

	// Middlewares
	app.Use(middleware.NewObservabilityMiddleware(
		logger.Default(),
		otel.TracerProvider.Tracer("demo-app"),
		otel.MeterProvider.Meter("demo-app"), // เพิ่มส่ง meter
	))
	app.Use(cors.New())
	app.Use(recover.New())

	// Init DI
	repo := repository.NewUserRepository()
	svc := service.NewUserService(repo)
	h := handler.NewUserHandler(svc)

	// Routes
	app.Get("/users/:id", h.GetUser)

	// Start
	app.Listen(":8080")
}