Route specific SSH traffic through a Docker VPN

docker-compose.yml

# This is useful to have an isolated VPN setup that lets you route SSH traffic
# without touching other traffic on the host.
#
# SETUP: 
#   mkdir ./config
#   cat ~/.ssh/id_rsa.pub > config/bastion_keys
#   cp path/to/your.ovpn config/
#   chmod 0700 config
#   chmod 0400 config/bastion_keys
#   chown -R 4096:4096 config
#
# USAGE: 
#   docker-compose up -d
#   ssh -J bastion@127.0.0.1:22222 example01
#
# PROTIP: 
# Configure jumphosts in your SSH config so you can do ssh vpn-example01 instead
#
#   Host vpn-example01
#     ProxyJump bastion@127.0.0.1:22222
#     HostName example01
#     Port 22

version: '3.7'
      
services: 
  vpn:
    image: dperson/openvpn-client:latest
    container_name: vpn
    restart: unless-stopped
    networks:
      - default
    read_only: true
    tmpfs:
      - /run
      - /tmp
    security_opt:
      - label:disable
    stdin_open: true
    tty: true
    cap_add:
      - NET_ADMIN
    environment:
      - TZ=America/Los_Angeles
    devices:
      - /dev/net/tun:/dev/net/tun
    volumes:
      - $PWD/config:/vpn:ro
    ports:
      - 22222:22/tcp
    healthcheck:
      test: ["CMD", "curl", "-Ss", "ifconfig.co"]
      interval: 60s
      timeout: 15s

  bastion:
    image: binlab/bastion
    container_name: bastion
    restart: unless-stopped
    depends_on:
      - vpn
    network_mode: "service:vpn"
    environment:
      PUBKEY_AUTHENTICATION: "true"
      GATEWAY_PORTS: "false"
      PERMIT_TUNNEL: "false"
      X11_FORWARDING: "false"
      TCP_FORWARDING: "true"
      AGENT_FORWARDING: "true"
      AUTHORIZED_KEYS: "/var/lib/bastion/config/bastion_keys"
    volumes:
      - $PWD/config:/var/lib/bastion/config:ro
      - bastion:/usr/etc/ssh:rw

networks:
  default:

volumes:
  bastion: