One docker image with openvpn:

1. at startup erases all routes except to VPN gateway and 8.8.8.8.

2. before and after connect it only has routes through VPN (no default ones - if vpn goes down, network goes down until re-established)

Start it like:

# ... --name vpn ...

Another docker image with what I want VPNed gets started with the network of the first

# ... --net container:vpn ...

I keep a browser within the second docker image (firefox) and use my main machine to show it. Note: you want to pass '--no-remote' to it and likely split /dev/shm

It can't really leak since it doesn't have routes to do anything other then through VPN.