Testing graceful shutdown with PID != 1 in Docker container

Dockerfile

FROM alpine:latest

WORKDIR /app

COPY . /app

ENTRYPOINT [ "ash", "entry.sh" ]

entry.sh

cd /app
./test_graceful

main.go

package main

import (
	"fmt"
	"os"
	"os/signal"
	"syscall"
)

func main() {
	fmt.Println("main started")
	shutdown := make(chan os.Signal, 2)
	signal.Notify(shutdown, syscall.SIGINT, syscall.SIGTERM)
	select {
	case s := <-shutdown:
		fmt.Println("shutdown server by received signal:", s.String())
	}
}

Makefile

build-app:
	GOOS=linux go build -o test_graceful main.go && \
	chmod +x test_graceful

build-image: build-app
	docker build -t test_graceful .

run-app-on-docker:
	docker run -it test_graceful

• Output when stop container (Ctr+C on terminal tab which running docker run ... command)

  ^Cshutdown server by received signal: interrupt
  

• Output when stop container by docker stop containerID

  #nothing
  

• Output of ps aux inside container (app run with PID = 7)

  /app # ps aux
  PID   USER     TIME  COMMAND
    1 root      0:00 ash entry.sh
    7 root      0:00 ./test_graceful
   15 root      0:00 ash
   21 root      0:00 ps aux
  

• Conclusion:
  • PID1 has to forward the signal to child process(es) (app) in case app is not running with PID1
  • The app MUST implement logic to handle signal from OS to be able to graceful shutdown.