How to use timeout in dockerfile with alpine base?

Context

I'm writing a dockerfile where I run a server application based on alpine:3.9 docker image. I test if my application is correctly installed by running it and sending a GET request with curl.

I send requests until I get an answer. So in case of trouble I want to timeout my tests using the built-in timeout function.

Pre-requirements

I'm using docker version 19.03.4, build 9013bf583a on debian.

Problem

The command:

docker run --rm -it alpine:3.9 timeout -t 2 /bin/sh -c 'sleep 5; echo "Not to be seen..."'

Exit displaying Not to be seen....

If I use timeout this way, the timeout seems to be ignored... I got the same problem if I put this in a docker file.

FROM alpine:3.9
RUN timeout -t 2 /bin/sh -c 'sleep 5; echo "Not to be seen..."'

docker build -t test .

Sending build context to Docker daemon  2.048kB
Step 1/2 : FROM alpine:3.9
 ---> 055936d39205
Step 2/2 : RUN timeout -t 2 /bin/sh -c 'sleep 5; echo "Not to be seen..."'
 ---> Running in 0fa22cd02173
Not to be seen...
Removing intermediate container 0fa22cd02173
 ---> e88107c3811b
Successfully built e88107c3811b
Successfully tagged test:latest

We can see the Not to be seen... displayed in console.

How to solve this issue ?

Reflexions / Tests

I test multiple things and the timeout function works well. It should be a problem when using it in dockerfile or passing it in docker run function...

When I try:

docker run --rm -it alpine:3.9 /bin/sh
# Then in container
timeout -t 2 /bin/sh -c 'sleep 5; echo "Not to be seen..."'

Exit with status code 143. And display Terminated.

When I try:

docker run --rm --name test -td alpine:3.9 /bin/sh
docker exec -it test timeout -t 2 /bin/sh -c 'sleep 5; echo "Not to be seen..."'

Exit with status code 143. Nothing displayed as expected.

Solution

Many programs drop default signal handlers when running as PID 1 (including /bin/sh).

You need to use the --init flag in order to make the container exit properly:

--init Run an init inside the container that forwards signals and reaps processes

This should work:

docker run --rm -it --init alpine:3.9 timeout -t 2 /bin/sh -c 'sleep 5; echo "Not to be seen..."'