OpenVPN-Cluster with Docker

Intro

This Docker image is based on Kyle Manna's openvpn image.

What it does

The idea was to create an openvpn server cluster without any load balancer. All servers are stated in the client configuration. If one server goes down the client tries to connect to the next server in the list. All clients can 'see' each other no matter to which they're connected. This is done by advertising the client's ip address to the cluster network (via broadcast). The entries for the routing table are added dynamically in each container.

Requirements

All containers have to be in the same subnet.
The server configuration and pki stuff must be shared between the containers.

How to

Initialize the openvpn server (read Kyle's guide)

Edit the openvpn server config:

topology subnet
script-security 2
learn-address /app/learn-address.sh

If you want to use the ovpn_genconfig script, modify OVPN_EXTRA_SERVER_CONFIG in /etc/openvpn/ovpn_env.sh:

declare -x OVPN_EXTRA_SERVER_CONFIG=([0]="script-security 2" [1]="topology subnet" [2]="learn-address /app/learn-address.sh"

Generate keys for clients and assign a static ip to them by adding a file for each client to /etc/openvpn/ccd/. The filename has to be identical to the client name used for the key generation.
```
ifconfig-push <static ip> <subnet>
```
The ip range and subnet are set in the server config.

Test setup

For testing purpose I started three containers usign the docker-compose.yml where every container has the same volume mounted to /etc/openvpn/. So I had three identical servers. The containers are connected to the compose network via interface eth0.

TODO

Figure out how to dynamically write the list of servers into the client config.
Dynamic client ip address assigment.