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

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