Unable to run Heroku exec on a docker container - docker

Question

I've followed the steps here (https://devcenter.heroku.com/articles/exec#enabling-docker-support) to install curl (curl 7.61.1 (x86_64-alpine-linux-musl) libcurl/7.61.1 LibreSSL/2.0.0 zlib/1.2.11 libssh2/1.8.0 nghttp2/1.32.0), python, bash, and openssh (OpenSSH_7.2p2-hpn14v4, OpenSSL 1.0.2p 14 Aug 2018). I've created the /app/.profile.d/heroku-exec.sh file in my container and added a sym link.
However, running heroku ps:exec -a my-app returns the following message:
Establishing credentials... error
! Could not connect to dyno!
! Check if the dyno is running with `heroku ps'
I've verified my application is in fact running (& has the runtime-heroku-exec feature enabled):
web (Free): /bin/sh -c exec\ java\ \$JAVA_OPTS\ -Dserver.port\=\$PORT\ -Djava.security.egd\=file:/dev/./urandom\ -jar\ /app.jar (1)
web.1: up 2018/09/30 09:34:55 -0600 (~ 4m ago)
I've verified that the heroku-exec.sh exists on my deployed container by doing heroku run -a my-app bash and cat /app/.profile.d/heroku-exec.sh
At this point, I'm not sure what to try in order to troubleshoot why heroku exec won't work on my container. Here's what my Dockerfile looks like in case there's something off with how I've put together my application:
FROM openjdk:8-jdk-alpine
RUN apk add --no-cache openssh-keygen
RUN apk add --no-cache openssh-client=7.2_p2-r5 --repository=http://dl-cdn.alpinelinux.org/alpine/v3.4/main --allow-untrusted
RUN apk add --no-cache openssh-sftp-server=7.2_p2-r5 --repository=http://dl-cdn.alpinelinux.org/alpine/v3.4/main --allow-untrusted
RUN apk add --no-cache openssh=7.2_p2-r5 --repository=http://dl-cdn.alpinelinux.org/alpine/v3.4/main --allow-untrusted
RUN apk add --no-cache curl
RUN apk add --no-cache bash
RUN apk add --update --no-cache python
RUN rm /bin/sh && ln -s /bin/bash /bin/sh
RUN adduser -D app-user
USER app-user
ARG JAR_FILE
ARG PORT
ARG HEROKU_FILE_NAME
COPY ${JAR_FILE} app.jar
COPY ${HEROKU_FILE_NAME} /app/.profile.d/heroku-exec.sh
ENV JAVA_OPTS -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=8000
HEALTHCHECK --interval=15m --timeout=10s --retries=3 --start-period=1m CMD curl --fail http://localhost:8080/restaurantscores/actuator/health || exit 1
CMD exec java $JAVA_OPTS -Dserver.port=$PORT -Djava.security.egd=file:/dev/./urandom -jar /app.jar

Answer 1

The "Using with Docker" section of the "Heroku Exec (SSH Tunneling)" documentation doesn't address Alpine usage.
Rather than using /app/.profile.d Alpine uses /etc/profile.d.
So change
COPY ${HEROKU_FILE_NAME} /app/.profile.d/heroku-exec.sh
to
COPY ${HEROKU_FILE_NAME} /etc/profile.d/heroku-exec.sh
Also ensure that heroku-exec.sh is executable. You can do this using chmod +x heroku-exec.sh.

Answer 2

I found that I had to additionally add a python symlink to my alpine-based dockerfile, to get it working:
ln -s /usr/bin/python3 /usr/bin/python
here is an example of a dockerfile, for deploying a very simple nginx application, that definitely works with heroku-exec (as of October 2020):
FROM alpine:latest
# install required packages
RUN apk add --no-cache --update python3 bash curl openssh nginx
# simplfy nginx config to enable ENV variable substitution
RUN echo 'server { listen PORT_NUMBER; }' > /etc/nginx/conf.d/default.conf \
&& mkdir /run/nginx
# 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 \
&& ln -s /usr/bin/python3 /usr/bin/python
# configure NGINX to listen on dynamic $PORT env variable supplied by Heroku.
CMD sed -i 's/PORT_NUMBER/'"$PORT"'/g' /etc/nginx/conf.d/default.conf; nginx -g 'daemon off;'