Shell into a Docker container running on a Heroku dyno. How? - docker

Question

Given a dyno in which a container is running, what's the Heroku equivalent of docker exec -it blarg /bin/bash? That is, how can one open a shell into the already-running container?
Example Dockerfile:
FROM heroku/heroku:16
CMD while true; do sleep 1; done
Example run:
$ heroku container:push my_app
<wait a minute>
$ heroku ps
=== my_app (Free): /bin/sh -c while\ true\;\ do\ sleep\ 1\;\ done (1)
my_app.1: up 2017/10/09 12:13:07 -0600 (~ 4m ago)
So far so good.
But now...
$ heroku ps:exec --dyno=my_app.1
Establishing credentials... error
▸ Could not connect to dyno!
▸ Check if the dyno is running with `heroku ps'
For good measure I check heroku ps at this point and it shows that the dyno is still running.
Yes, I've done all the things Heroku suggests to enable Docker support. Per the documentation, I have tried using a base image of my choice while ensuring that bash, curl, openssh, and python are present. I have also tried using the Heroku-16 base image, as shown in the above example.
(The linked documentation also references steps required for Private Spaces. Since I'm not using Private Spaces I have not applied those steps.)

Answer 1

EDIT CIRCA 2022 This was the accepted answer in 2017. I'm not so sure anymore, so I'm unaccepting my answer here to avoid misleading anyone. I'm not fiddling with Heroku + Docker these days, so I'm not in a good position to accept an answer.
TL;DR Ensure that bash is installed in the image and add this to your Dockerfile:
RUN rm /bin/sh && ln -s /bin/bash /bin/sh
Explanation
Contrary to what the documentation would lead one to believe, Heroku does not, out of the box, support heroku ps:exec into a Docker container already running in a dyno.
Quoting from responses I have received from the Heroku team:
Our ps:exec feature ... works ... by injecting a bash file into dynos,
opening an additional port in the background, and allowing you to
connect to it.
[T]he default
shell used by Docker is /bin/sh, which is not compatible with the
Heroku Exec script (it's requires /bin/bash).
There is a workaround you can use though. Put the following in your
Dockerfile:
RUN rm /bin/sh && ln -s /bin/bash /bin/sh
This is definitely a gap in
our product, and we'll work to make this better.

Answer 2

If bash is installed, run heroku run bash. This will get you into the shell from your command line.
You can also use the GUI and go to "More" -> "Run Console" on your heroku app, and input "bash" to bring it up there.

Answer 3

Edited:
In order to run heroku ps:exec on apps with Docker and deployed via the Container Registry you have to enable runtime-heroku-exec.
You can do heroku features:enable runtime-heroku-exec to enable it
Here you can see the documentation of exec with the instructions to enable docker support

Answer 4

in my situation, to get this working with Ubuntu 20.04 (focal), i had to additionally install the python-is-python3 package into the docker image, to get heroku-exec working.
here is a working example (october 2020) of an ubuntu-based dockerfile, that works with heroku-exec:
FROM ubuntu:focal
# install required packages
RUN export DEBIAN_FRONTEND=noninteractive && apt-get update && apt-get install -y python3 curl python-is-python3 openssh-server iproute2 nginx && apt-get clean
# simplfy nginx config to enable ENV variable substitution
RUN echo 'server { listen PORT_NUMBER; }' > /etc/nginx/sites-enabled/default
# add config required for HEROKU_EXEC
# ENV HEROKU_EXEC_DEBUG=1
RUN rm /bin/sh \
&& ln -s /bin/bash /bin/sh \
&& mkdir -p /app/.profile.d/ \
&& printf '#!/usr/bin/env bash\n\nset +o posix\n\n[ -z "$SSH_CLIENT" ] && source <(curl --fail --retry 7 -sSL "$HEROKU_EXEC_URL")\n' > /app/.profile.d/heroku-exec.sh \
&& chmod +x /app/.profile.d/heroku-exec.sh
# configure NGINX to listen on dynamic $PORT env variable supplied by Heroku.
CMD sed -i 's/PORT_NUMBER/'"$PORT"'/g' /etc/nginx/sites-enabled/default; nginx -g 'daemon off;'
then connect with this command:
heroku ps:exec -a name-of-app-12345

Answer 5

Both heroku run /bin/bash and heroku ps:exec won't work in my situation. The former opens a new container which is different from the real one running! The latter just doesn't work in my container of alpine3, though heroku features:enable runtime-heroku-exec can succeed. My solution is to bring up a shell server and a traffic forwarder in the container. Then on the client connect to the shell server with tunnel created by traffic forwarder.
traffic flow:
localhost:2023 -> chisel client -> ...tunnel... -> chisel server -> localhost:8182
In conainer, start up a shell server with socat and a tunnel server with chisel:
nohup socat tcp-l:8182,reuseaddr,fork exec:/bin/bash,pty,setsid,setpgid,stderr,ctty > /tmp/socat.log 2>&1 &
nohup ./chisel server --port $PORT --proxy http://httpbin.org > /tmp/chisel.log 2>&1 &
On client side, start a chisel client to forward traffic from localhost:8182 to the socat on the server
chisel client http://yourapp.herokuapp.com/ 0.0.0.0:2023:localhost:8182
on client side, open another terminal window:
socat -,raw,echo=0 tcp:127.0.0.1:2023
How to get the chisel on server? Download it or just compile from source in Dockerfile
download chisel

Answer 6

One probably root cause is the docker not running in detached mode on Heroku.
https://docs.docker.com/language/nodejs/run-containers/#run-in-detached-mode
Have someone do know how to activate -d option when the container is being executed by Heroku?