aws_spot_main.go

package main

import (
	"context"
	"log"
	"math/rand"
	"os"
	"runtime/trace"
	"sync"
	"time"
)

type Application struct {
	done chan struct{}
}

func New() *Application {
	return &Application{make(chan struct{}, 1)}
}

func (a *Application) Start(ctx context.Context, wg *sync.WaitGroup) chan struct{} {
	go func() {
		select {
		case <-ctx.Done():
			log.Println("Started goroutine received a cancellation order")
		case <-time.After(15 * time.Minute):
			log.Println("Yikes")
		}
		a.done <- struct{}{}
		wg.Done()
	}()
	return a.done
}

func main() {
	rand.Seed(time.Now().UnixNano())
	traceFile, err := os.Create("/tmp/aws_spot_main.trace")
	if err != nil {
		log.Fatalln("could not create a temp file")
	}
	trace.Start(traceFile)
	defer trace.Stop()
	ctx, cancel := context.WithCancel(context.Background())
	ticker := time.NewTicker(1 * time.Second)
	app := New()
	wg := &sync.WaitGroup{}
	wg.Add(1)
	done := app.Start(ctx, wg)
	for {
		select {
		case <-done:
			log.Println("app completed successfully and normally")
			wg.Wait()
			log.Println("exiting the main function. All goroutines shutdown")
			ticker.Stop()
			return
		case <-ticker.C:
			log.Println("checking AWS spot instance termination notice")
			if rand.Intn(10) == 0 {
				log.Println("sending cancel message")
				cancel()
			} else {
				log.Println("keep running")
			}
		}
	}
}