[Unit]
Description=OpenVPN Docker Container
Documentation=https://github.com/kylemanna/docker-openvpn
After=network.target docker.socket
Requires=docker.socket

[Service]
# Modify IP6_PREFIX to match network config
Environment="IP6_PREFIX=2001:db8::/64"
Environment="OVPN_NAME=openvpn0"
Environment="OVPN_DATA=ovpn-data"

# Clean-up previous bad states
ExecStartPre=-/usr/bin/docker rm -f openvpn0

# Ensure forwarding is enabled on host's networking stack (hacky)
ExecStartPre=/sbin/sysctl net.ipv6.conf.default.forwarding=1
ExecStartPre=/sbin/sysctl net.ipv6.conf.all.forwarding=1

# Main process
ExecStart=/usr/bin/docker run --rm --privileged --volumes-from $OVPN_DATA --name $OVPN_NAME -p 1194:1194/udp kylemanna/openvpn:dev ovpn_run --config openvpn.conf --server-ipv6 $IP6_PREFIX

# Add static route for IPv6 after it starts up
ExecStartPost=/bin/sh -c "sleep 1; ip route replace $IP6_PREFIX via $(docker inspect -f '{{ .NetworkSettings.GlobalIPv6Address }}' $OVPN_NAME ) dev docker0"

# Clean-up
ExecStopPost=-/sbin/ip route del $IP6_PREFIX dev docker0

[Install]
WantedBy=multi-user.target