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OpenVPN for Docker

Based on jpetazzo/dockvpn.

Quick instructions:

docker-compose up -d

Once provisioned, navigate to http://<Your IP>:10889 to access a single-use download of your OpenVPN config. It will only be available for a single download, requiring that OpenVPN be re-deployed (and thus, re-keyed and new certs generated).

Using this setup with DigitalOcean

or any provider supporting provisioning scripts

To use this configuration with a provider such as DigitalOcean, use provision.sh in your user-data field when you create a new droplet.

How does it work?

When the dockvpn image is started, it generates:

  • Diffie-Hellman parameters,
  • a private key,
  • a self-certificate matching the private key,
  • two OpenVPN server configurations (for UDP and TCP),
  • an OpenVPN client profile.

Then, it starts two OpenVPN server processes (one on 1194/udp, another on 443/tcp).

The configuration is located in /etc/openvpn, and the Dockerfile declares that directory as a volume. It means that you can start another container with the --volumes-from flag, and access the configuration. Conveniently, the modified dockvpn image comes with a script called serveconfig, which starts a pseudo HTTPS server on 8080/tcp. The pseudo server does not even check the HTTP request; it just sends the HTTP status line, headers, and body right away.

Because this interface is only exposed to the Docker network, and is configured (by design) to terminate after serving a single request (ensuring that you are aware if, either, someone has already accessed and downloaded your config, and that you can act if your config is unavailable), it is only accessible to the vpn-config-ui container, which will serve a single copy of your config to you at http://<Server IP Address>:10889. All subsequent requests will fail to download, as serveconfig will have been terminated.

OpenVPN details

We use tun mode, because it works on the widest range of devices. tap mode, for instance, does not work on Android, except if the device is rooted.

The topology used is net30, because it works on the widest range of OS. p2p, for instance, does not work on Windows.

The TCP server uses 192.168.255.0/25 and the UDP server uses 192.168.255.128/25.

The client profile specifies redirect-gateway def1, meaning that after establishing the VPN connection, all traffic will go through the VPN. This might cause problems if you use local DNS recursors which are not directly reachable, since you will try to reach them through the VPN and they might not answer to you. If that happens, use public DNS resolvers like those of Google (8.8.4.4 and 8.8.8.8) or OpenDNS (208.67.222.222 and 208.67.220.220).

Security discussion

For simplicity, the client and the server use the same private key and certificate. This is certainly a terrible idea. If someone can get their hands on the configuration on one of your clients, they will be able to connect to your VPN, and you will have to generate new keys. Which is, by the way, extremely easy, since each time you docker-compose the OpenVPN compose file, a new key is created. If someone steals your configuration file (and key), they will also be able to impersonate the VPN server (if they can also somehow hijack your connection).

It would probably be a good idea to generate two sets of keys.

It would probably be even better to generate the server key when running the container for the first time (as it is done now), but generate a new client key each time the serveconfig command is called. The command could even take the client CN as argument, and another revoke command could be used to revoke previously issued keys.

Verified to work with ...

People have successfully used this VPN server with clients such as:

  • OpenVPN on Linux, (Note: sudo openvpn client.ovpn will run this configuration)
  • Viscosity on OSX (#25),
  • Tunnelblick on OSX,
  • (some VPN client on Android but I can't remember which).

Other related/interesting projects

  • @besn0847/alpinevpn, a smaller image based on the Alpine distribution

  • The obvious inspiration for my interest in this jpetazzo/dockvpn

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