CODEWITHSUNDEEP
dockergodockerfile
Anthony Kong
Anthony Kong

Reputation: 40834

Unable to gracefully shutdown a docker process

I want to be able to shutdown a docker process gracefully. I derived the these files by following the idea in this blog post: https://husobee.github.io/golang/ecs/2016/05/19/ecs-graceful-go-shutdown.html

Here are my files

1) Dockerfile

FROM debian:jessie
ADD app /app
RUN apt-get update --fix-missing
RUN apt-get install -y golang
CMD ["go", "run", "/app/main.go"]

2) app/main.go

package main

import "os"
import "syscall"
import "fmt"
import "time"
import "os/signal"


func main() {
    // create a "returnCode" channel which will be the return code of the application
    var returnCode = make(chan int)

    // finishUP channel signals the application to finish up
    var finishUP = make(chan struct{})

    // done channel signals the signal handler that the application has completed
    var done = make(chan struct{})

    // gracefulStop is a channel of os.Signals that we will watch for -SIGTERM
    var gracefulStop = make(chan os.Signal)

    // watch for SIGTERM and SIGINT from the operating system, and notify the app on
    // the gracefulStop channel
    signal.Notify(gracefulStop, syscall.SIGTERM)
    signal.Notify(gracefulStop, syscall.SIGINT)

    // launch a worker whose job it is to always watch for gracefulStop signals
    go func() {
        // wait for our os signal to stop the app
        // on the graceful stop channel
        // this goroutine will block until we get an OS signal
        sig := <-gracefulStop
        fmt.Printf("caught sig: %+v", sig)

        // send message on "finish up" channel to tell the app to
        // gracefully shutdown
        finishUP<-struct{}{}

        // wait for word back if we finished or not
        select {
        case <-time.After(30*time.Second):
            // timeout after 30 seconds waiting for app to finish,
            // our application should Exit(1)
            returnCode<-1
        case <-done:
            // if we got a message on done, we finished, so end app
            // our application should Exit(0)
            returnCode<-0
        }
    }()


    // ... Do business Logic in goroutines

    fmt.Println("waiting for finish")
    // wait for finishUP channel write to close the app down
    <-finishUP
    fmt.Println("stopping things, might take 2 seconds")

    // ... Do business Logic for shutdown simulated by Sleep 2 seconds
    time.Sleep(2*time.Second)

    // write to the done channel to signal we are done.
    done <-struct{}{}
    os.Exit(<-returnCode)
}

I build the image by running

docker build -f Dockerfile -t docker-shutdown .

I start a container by 

docker run  docker-shutdown

Then I try to shut it down by

docker stop <container id>

In the console that runs 'docker run', I can see:

waiting for finish

and it just terminated with no further output.

I would expect to see at least some output like

 caught sig <SIGNAL_VALUE>

So why my expected behavior did not happen? I am also new to go so I am not sure if it may have something to do with the go code or the CMD definition in the Dockerfile.

My question:

Why the go process cannot catch the either TERM and KILL signals?

Upvotes: 4

Views: 2429

Answers (1)

mhb
mhb

Reputation: 773

go run is getting the signal, not the program that is being run.

Compile the program ahead of time and run the binary directly in docker, and it will work as expected.

Upvotes: 4

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