Say for example you have a MySQL server running on the host machine and want your docker container to be able to connect to it.

When using docker-compose the following config in the yaml will allow this.

extra_hosts:

version "3"
services 
  app:
    image: your/image:latest
    extra_hosts:
      - "host.docker.internal:host-gateway"

Now, inside your container to connect to the host use the address :

host.docker.internal

My scenario for requiring this, I have gluetun running as a container which connects to a wireguard VPN and also a socks5 proxy. All traffic in this container goes via the VPN.

I have a different container which I want to sit outside of the VPN, and those apps all communicate together. One of these proxies external requests via socks5. If I move that app to the gluetun compose the other apps can no longer see it.

• https://hub.docker.com/r/qmcgaw/gluetun
• https://hub.docker.com/r/serjs/go-socks5-proxy/