Docker - how to send input to a program via the API

Question

I have been using Docker's remote API to create a container, run a Python program in it, attach to the container and stream the output written to stdout to the web.

Now, I wanted my Python program to accept user input from stdin. E.g.

import sys
name = sys.stdin.readline()
print "Your name is: " + name

How do I pass the user input to this Python program running inside a Docker container via the API? I don't see any API end-points which will allow me to pass "input" to a process running inside a docker container.

Thanks.

Answer 1

You can in fact attach the stdin of a container using docker attach. Example:

Start a "listening" container:

docker run -i -t ubuntu:precise /bin/bash -c 'read FOO; echo $FOO;'

Then in another terminal:

# lookup container id
docker ps

# attach the container
docker attach 91495c6374b1

You are now hooked to the listening container's stdin and can type thing and everything should work.

As to doing that using the remote API... I think this is possible using the /containers/{id}/attach endpoint with stdin=1 and possibly stream=1. Couldn't get it to work and still working on understanding the go code behind this, but from what I can see in the implementation this should definitely be possible.