Use docker container as SSH tunnel inside network

Question

I am trying to use a docker container to set up a SSH tunnel to a remote database that is only reachable via SSH. I have a docker network with several containers and want to make the database available for all the containers in the network.

The Dockerfile for the SSH container looks like this:

FROM debian:stable

RUN apt-get update && apt-get -y --force-yes install openssh-client autossh postgresql-client

COPY .ssh /root/.ssh
RUN chown root:root /root/.ssh/config

EXPOSE 12345
ENTRYPOINT ["/usr/bin/autossh", "-M", "0", "-v", "-T", "-N", "-4", "-L", "12345:localhost:1234", "user@remotedb" ]

Inside the .ssh diretctory are my keys and the config file, which looks like that:

Host remotedb
    StrictHostKeyChecking   no
    ServerAliveInterval     30
    ServerAliveCountMax     3

The tunnel itself works on this container, meaning I can access the db from inside it as localhost:12345.

Now I want to access it also from other containers in the same network.

My docker-compose.yml looks like this (I commented out some trials):

version: '2'

networks:
  my_network:
    driver: bridge
    ipam:
     config:
       - subnet: 10.12.0.0/16
         gateway: 10.12.0.1

services:
  service_1:
    image: my/image:alias
    volumes:
      - somevolume
#   links:
#      - my_ssh
    ports:
      - "8080"    
    environment:
      ENV1: blabla
    networks:
      my_network:
         ipv4_address: 10.12.0.12

  my_ssh:
    build:
      context: ./dir_with_Dockerfile
#   ports:
#     - "23456:12345"
    expose:
      - "12345"
    networks:
      my_network:
         ipv4_address: 10.12.0.13

I've tried to access the remote database from inside service_1 with hostnames 'my_ssh', the ipv4_address, 'localhost', and with ports 12345 and 23456. None of these combinations have worked. Where could I go wrong?

Or how else could I achieve a permanent connection from my containers to the remote database?

Answer 1

More of a suggestion than an answer; setting up OpenVPN on your database network and your docker swarm would allow you to connect the two networks together. It would also make it easier for you to configure more hosts in the future.