OpenVPN Client for Docker

What is this and what does it do?

ghcr.io/wfg/openvpn-client is a containerized OpenVPN client. It has a kill switch built with iptables that kills Internet connectivity to the container if the VPN tunnel goes down for any reason. It also includes an HTTP proxy server (Tinyproxy) and a SOCKS proxy server (Dante). This allows hosts and non-containerized applications to use the VPN without having to run VPN clients on those hosts.

This image requires you to supply the necessary OpenVPN configuration file(s). Because of this, any VPN provider should work.

If you find something that doesn't work or have an idea for a new feature, issues and pull requests are welcome.

Why?

Having a containerized VPN client lets you use container networking to easily choose which applications you want using the VPN instead of having to set up split tunnelling. It also keeps you from having to install an OpenVPN client on the underlying host.

The idea for this image came from a similar project by qdm12 that has since evolved into something bigger and more complex than I wanted to use. I decided to dissect it and take it in my own direction. I plan to keep everything here well-documented so this is not only a learning experience for me, but also anyone else that uses it.

How do I use it?

Getting the image

You can either pull it from GitHub Container Registry or build it yourself.

To pull it from GitHub Container Registry, run

docker pull ghcr.io/wfg/openvpn-client

To build it yourself, run

docker build -t ghcr.io/wfg/openvpn-client https://github.com/wfg/docker-openvpn-client.git

Creating and running a container

The image requires the container be created with the NET_ADMIN capability and /dev/net/tun accessible. Below are bare-bones examples for docker run and Compose; however, you'll probably want to do more than just run the VPN client. See the sections below to learn how to use the proxies and have other containers use openvpn-client's network stack.

docker run

docker run --detach \
  --name=openvpn-client \
  --cap-add=NET_ADMIN \
  --device=/dev/net/tun \
  --env KILL_SWITCH=off \
  --volume <path/to/config/dir>:/data/vpn \
  ghcr.io/wfg/openvpn-client

docker-compose

services:
  openvpn-client:
    image: ghcr.io/wfg/openvpn-client
    container_name: openvpn-client
    cap_add:
      - NET_ADMIN
    devices:
      - /dev/net/tun
    environment:
      - KILL_SWITCH=off
    volumes:
      - <path/to/config/dir>:/data/vpn
    restart: unless-stopped

Environment variables

Variable	Default (blank is unset)	Description
KILL_SWITCH	on	The on/off status of the network kill switch.
SUBNETS		A list of one or more comma-separated subnets (e.g. 192.168.0.0/24,192.168.1.0/24) to allow outside of the VPN tunnel. See important note about this below.
VPN_CONFIG_FILE		The OpenVPN config file to use. If this is unset, the first file with the extension .conf will be used.
VPN_LOG_LEVEL	3	OpenVPN verbosity (1-11)
HTTP_PROXY	off	The on/off status of Tinyproxy, the built-in HTTP proxy server. To enable, set to on. Any other value (including unset) will cause the proxy server to not start. It listens on port 8080.
SOCKS_PROXY	off	The on/off status of Dante, the built-in SOCKS proxy server. To enable, set to on. Any other value (including unset) will cause the proxy server to not start. It listens on port 1080.
PROXY_USERNAME		Credentials for accessing the proxies. If PROXY_USERNAME is specified, you must also specify PROXY_PASSWORD.
PROXY_PASSWORD		Credentials for accessing the proxies. If PROXY_PASSWORD is specified, you must also specify PROXY_USERNAME.
PROXY_USERNAME_SECRET		Docker secrets that contain the credentials for accessing the proxies. If PROXY_USERNAME_SECRET is specified, you must also specify PROXY_PASSWORD_SECRET.
PROXY_PASSWORD_SECRET		Docker secrets that contain the credentials for accessing the proxies. If PROXY_PASSWORD_SECRET is specified, you must also specify PROXY_USERNAME_SECRET.

Environment variable considerations

SUBNETS

Important: If the kill switch is enabled, the DNS server used by this container prior to VPN connection must be included in the value specified. For example, if your container is using 192.168.1.1 as a DNS server, then this address or an appropriate CIDR block must be included in SUBNETS. This is necessary because the kill switch blocks traffic outside of the VPN tunnel before it's actually established. If the DNS server is not allowed, the server addresses in the VPN configuration will not resolve.

The subnets specified will be allowed through the firewall which allows for connectivity to and from hosts on the subnets.

HTTP_PROXY and SOCKS_PROXY

If enabling the the proxy server(s), you'll want to publish the appropriate port(s) in order to access the server(s). To do that using docker run, add -p <host_port>:8080 and/or -p <host_port>:1080 where <host_port> is whatever port you want to use on the host. If you're using docker-compose, add the relevant port specification(s) from the snippet below to the openvpn-client service definition in your Compose file.

ports:
  - <host_port>:8080
  - <host_port>:1080

PROXY_USERNAME_SECRET and PROXY_PASSWORD_SECRET

Compose has support for Docker secrets. See the Compose file in this repository for example usage of passing proxy credentials as Docker secrets.

Using with other containers

Once you have your openvpn-client container up and running, you can tell other containers to use openvpn-client's network stack which gives them the ability to utilize the VPN tunnel. There are a few ways to accomplish this depending how how your container is created.

If your container is being created with

1. the same Compose YAML file as openvpn-client, add network_mode: service:openvpn-client to the container's service definition.
2. a different Compose YAML file than openvpn-client, add network_mode: container:openvpn-client to the container's service definition.
3. docker run, add --network=container:openvpn-client as an option to docker run.

Once running and provided your container has wget or curl, you can run docker exec <container_name> wget -qO - ifconfig.me or docker exec <container_name> curl -s ifconfig.me to get the public IP of the container and make sure everything is working as expected. This IP should match the one of openvpn-client.

Handling ports intended for connected containers

If you have a connected container and you need to access a port that container, you'll want to publish that port on the openvpn-client container instead of the connected container. To do that, add -p <host_port>:<container_port> if you're using docker run, or add the below snippet to the openvpn-client service definition in your Compose file if using docker-compose.

ports:
  - <host_port>:<container_port>

In both cases, replace <host_port> and <container_port> with the port used by your connected container.

Verifying functionality

Once you have container running ghcr.io/wfg/openvpn-client, run the following command to spin up a temporary container using openvpn-client for networking. The wget -qO - ifconfig.me bit will return the public IP of the container (and anything else using openvpn-client for networking). You should see an IP address owned by your VPN provider.

docker run --rm -it --network=container:openvpn-client alpine wget -qO - ifconfig.me