for gluetun
https://stackoverflow.com/questions/59340558/route-docker-container-traffic-through-a-vpn-container
for nginx-proxy
https://github.com/nginx-proxy/nginx-proxy
https://github.com/nginx-proxy/docker-gen
http://jasonwilder.com/blog/2014/03/25/automated-nginx-reverse-proxy-for-docker/

2023
https://blog.bartzz.com/how-to-route-docker-container-through-another-container/
    --network container:<name>
    network_mode: service:<name>

FROM ubuntu:20.04
RUN apt-get update && apt-get install -y \
    iproute2 iptables openvpn
CMD ["sh"]

docker build -t my-router .
docker run --cap-add=NET_ADMIN --device /dev/net/tun -d --name my-container my-router
# --device list  Add a host device to the container
# --privileged --net=host

docker exec -it my-container bash
echo 1 > /proc/sys/net/ipv4/ip_forward
echo "net.ipv4.ip_forward = 1" >> /etc/sysctl.conf
# if NAT is needed, where eth0 - output inet device
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
exit

# at host
docker inspect my-container | grep '"IPAddress"'
docker inspect -f '{{range.NetworkSettings.Networks}}{{.IPAddress}}{{end}}' container_name
CONTAINER_IP=$(docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' my-container)
# something like  172.17.0.2

ip route add default via <IP_CONTAINER> dev docker0

******************************************

docker bridge network does not support fixed ip-addresses
    docker network create \
      --subnet=192.168.1.0/24 \
      my_custom_network

    docker run --rm -dit \
      --net my_custom_network \
      --ip 192.168.1.100 \
      --name my_container \
      nginx

    docker inspect -f '{{range.NetworkSettings.Networks}}{{.IPAddress}}{{end}}' my_container