How to hide open port behind vpn using docker container?

Question

Asterisk

I use freepbx as a docker container. I noticed the attack, there is a brute force search of passwords. I want to hide my asterisk server behind openvpn. I tried to raise two docker containers on my own. Now I'm just going to share the result.
What I did:

1. created a new network with the command docker create network mynet

2. launched openvpn container hub.docker.com/r/kylemanna/openvpn

3. launched the freepbx container hub.docker.com/r/murf66/freepbx, with the --net=mynet parameter
4. connected to vpn, found my freepbx via nmap, could not connect to it
Be it freepbx, wordpress, something else . How to hide something behind vpn using docker?