ssh docker

Dockerfile

FROM debian:stretch

# Remove the host keys because it's not safe to package those. The entrypoint
# will establish a convention for providing them in the environment and
# generating new ones automatically.
RUN apt update && \
    apt install --assume-yes ssh && \
    rm /etc/ssh/ssh_host_* && \
    rm -rf /var/lib/apt/lists/*

ADD ./entrypoint /bin/entrypoint

ENTRYPOINT [ "entrypoint" ]

entrypoint

#!/bin/bash

# If this is a server, then we need the HOST_KEYS and AUTHORIZED_KEYS
# environment variables set. If it's a client, we need the ID_RSA variable set.
#
# I'm checking if the environment variable is set with this +x thing:
# https://stackoverflow.com/a/13864829/8710

if [[ -z ${HOST_KEYS+x} && -z ${AUTHORIZED_KEYS+x} && -z ${ID_RSA+x} ]]; then
    echo
    echo "This is a Docker image with both client and server modes."
    echo
    echo "If you want a server set, in your environment: HOST_KEYS and AUTHORIZED_KEYS"
    echo
    echo "If you want a client, set: ID_RSA"
    echo
    echo "Here's some pregenerated values for you."
    echo
    echo "ID_RSA=$(ssh-keygen -P '' -f /tmp/id_rsa 1>/dev/null 2>&1; cat /tmp/id_rsa | gzip | base64 -w 0)"
    echo
    echo "HOST_KEYS=$(dpkg-reconfigure openssh-server >/dev/null 2>&1; tar --create /etc/ssh/ssh_host_* 2>/dev/null | gzip | base64 -w 0)"
    echo
    echo "AUTHORIZED_KEYS=$(cat /tmp/id_rsa.pub | gzip | base64 -w 0)"
    echo
    exit 1
fi

if [[ ! -z ${HOST_KEYS+x} ]]; then
    echo "Extracting HOST_KEYS."
    echo $HOST_KEYS | base64 -d | gunzip | tar --directory / --extract
fi

if [[ ! -z ${AUTHORIZED_KEYS+x} ]]; then
    echo "Extracting AUTHORIZED_KEYS."
    mkdir -p /root/.ssh
    echo $AUTHORIZED_KEYS | base64 -d | gunzip > /root/.ssh/authorized_keys
fi

if [[ ! -z ${ID_RSA+x} ]]; then
    echo "Extracting ID_RSA."
    mkdir -p /root/.ssh
    echo $ID_RSA | base64 -d | gunzip > /root/.ssh/id_rsa
    chmod 400 /root/.ssh/id_rsa
fi

if [[ $# -eq 0 ]]; then
    echo "Starting SSH server."
    service ssh start
    tail -f /dev/null
else
    # Run whatever is asked for!
    echo "Running a user command."
    "$@"
fi