The most likely candidate issue is that Docker manages your /etc/resolv.conf inside the container. Generally speaking, when you connect to a VPN, you need to change that. Does your /etc/resolv.conf get updated when your VPN connects liteblue?
I did play with this image some time ago.
I do remember getting it working, but I don’t recall if I tested any internally resolvable IPs.
Cheers!