##  get a container-name with `docker ps`
docker exec -it <container-name> sh

# see what interfaces have started. if tun0 is not listed, 
# there was an error starting a VPN connection
ip addr show

# see what ports have services bound to them. dante
# should be listed here using port 1080/tcp
ss -tlpn

# list running processes. you should see supervisor, 
# openvpn, and several entries from dante
ps aux

# Tail the STDOUT of failing programs
supervisorctl tail (openvpn|dante)

# Tail supervisord error logs
tail /var/log/supervisord.log