go-http-server-with-otel/main.go

// This template contains a simple
// app with OTEL bootstrap that will create an
// HTTP server configured by environment that exports
// spans and metrics to an OTEL collector if configured
// to do so. Will also stand up a prometheus metrics
// endpoint.
//
// Configuration and logger stored in context
// Reference implementation of the provided packages
package main

import (
	"context"
	"net/http"
	"os"
	"os/signal"
	"sync"
	"time"

	"github.com/rs/zerolog"
	"go.opentelemetry.io/otel/codes"
	"go.opentelemetry.io/otel/trace"
	"golang.org/x/sys/unix"

	"gitea.libretechconsulting.com/rmcguire/go-http-server-with-otel/pkg/config"
	"gitea.libretechconsulting.com/rmcguire/go-http-server-with-otel/pkg/logging"
	"gitea.libretechconsulting.com/rmcguire/go-http-server-with-otel/pkg/otel"
	"gitea.libretechconsulting.com/rmcguire/go-http-server-with-otel/pkg/srv"
)

var (
	cfg    *config.AppConfig
	l      *zerolog.Logger
	tracer trace.Tracer
)

func main() {
	ctx, cncl := signal.NotifyContext(context.Background(), os.Interrupt, unix.SIGTERM)
	defer cncl()

	shutdownFuncs := make([]func(context.Context) error, 0)

	// Load configuration and setup logging
	ctx = setupConfigAndLogging(ctx)

	// Set up OTEL
	ctx, otelShutdown := otel.Init(ctx)
	shutdownFuncs = append(shutdownFuncs, otelShutdown)
	tracer = otel.MustTracerFromCtx(ctx)

	// Start App
	ctx, initSpan := tracer.Start(ctx, "init")

	// Start HTTP Server
	dummyFuncs := []srv.HTTPFunc{
		{
			Path: "/dummy",
			HandlerFunc: func(w http.ResponseWriter, r *http.Request) {
				w.Write([]byte("hello world"))
			},
		},
	}
	httpShutdown, httpDone := srv.MustInitHTTPServer(ctx, dummyFuncs...)
	shutdownFuncs = append(shutdownFuncs, httpShutdown)

	// Startup Complete
	l.Info().
		Str("name", cfg.Name).
		Str("version", cfg.Version).
		Str("logLevel", cfg.Logging.Level).
		Msg("app initialized")
	initSpan.SetStatus(codes.Ok, "")
	initSpan.End()

	// Wait for signal
	select {
	case <-httpDone:
		l.Warn().Msg("shutting down early on http server done")
	case <-ctx.Done():
		l.Warn().Str("reason", ctx.Err().Error()).
			Msg("shutting down on context done")
	}
	shutdown(shutdownFuncs...)
}

func shutdown(shutdownFuncs ...func(context.Context) error) {
	now := time.Now()

	doneCtx, cncl := context.WithTimeout(context.Background(), 15*time.Second)
	defer func() {
		if doneCtx.Err() == context.DeadlineExceeded {
			l.Err(doneCtx.Err()).
				Dur("shutdownTime", time.Since(now)).
				Msg("app shutdown aborted")
		} else {
			l.Info().
				Int("shutdownFuncsCalled", len(shutdownFuncs)).
				Dur("shutdownTime", time.Since(now)).
				Msg("app shutdown normally")
		}
		cncl()
	}()

	doneCtx, span := tracer.Start(doneCtx, "shutdown")
	defer span.End()

	var wg sync.WaitGroup
	wg.Add(len(shutdownFuncs))

	for _, f := range shutdownFuncs {
		go func() {
			defer wg.Done()
			err := f(doneCtx)
			if err != nil {
				span.SetStatus(codes.Error, "shutdown failed")
				span.RecordError(err)
				l.Err(err).Send()
			}
		}()
	}

	wg.Wait()
}

func setupConfigAndLogging(ctx context.Context) context.Context {
	ctx, err := config.LoadConfig(ctx)
	if err != nil {
		panic(err)
	}

	cfg = config.MustFromCtx(ctx)
	ctx = logging.MustInitLogging(ctx)
	l = zerolog.Ctx(ctx)

	l.Trace().Any("config", *cfg).Send()
	return ctx
}