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https://github.com/umputun/dockvpn

Recipe to build an OpenVPN image for Docker
https://github.com/umputun/dockvpn

Last synced: 3 months ago
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Recipe to build an OpenVPN image for Docker

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# OpenVPN for Docker



**the original project - [jpetazzo/dockvpn](https://github.com/jpetazzo/dockvpn)** and it has its own [automatic build on dockerhub](https://hub.docker.com/r/jpetazzo/dockvpn/).



Quick instructions:



```bash

CID=$(docker run -d --privileged -p 1194:1194/udp -p 443:443/tcp umputun/dockvpn)

docker run -t -i -p 8080:8080 --volumes-from $CID umputun/dockvpn serveconfig

```



Or run without logs:



```bash

CID=$(docker run -d --privileged -p 1194:1194/udp -p 443:443/tcp -e "DISABLE_LOGS=1" --log-driver none umputun/dockvpn)

docker run -t -i -p 8080:8080 -e "DISABLE_LOGS=1" --log-driver none --volumes-from $CID umputun/dockvpn serveconfig

```



Download file with `curl`:

```bash

curl -k https://[SERVER_IP]:8080/ > ~/openvpn.ovpn

```



Now download the file located at the indicated URL. You will get a

certificate warning, since the connection is done over SSL, but we are

using a self-signed certificate. After downloading the configuration,

stop the `serveconfig` container. You can restart it later if you need

to re-download the configuration, or to download it to multiple devices.



The file can be used immediately as an OpenVPN profile. It embeds all the

required configuration and credentials. It has been tested successfully on

Linux, Windows, and Android clients. If you can test it on OS X and iPhone,

let me know!



**Note:** there is a [bug in the Android Download Manager](

http://code.google.com/p/android/issues/detail?id=3492) which prevents

downloading files from untrusted SSL servers; and in that case, our

self-signed certificate means that our server is untrusted. If you

try to download with the default browser on your Android device,

it will show the download as "in progress" but it will remain stuck.

You can download it with Firefox; or you can transfer it with another

way: Dropbox, USB, micro-SD card...



If you reboot the server (or stop the container) and you `docker run`

again, you will create a new service (with a new configuration) and

you will have to re-download the configuration file. However, you can

use `docker start` to restart the service without touching the configuration.



## How does it work?



When the `jpetazzo/openvpn` 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, `jpetazzo/openvpn` 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.



## 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 run` the OpenVPN

image, 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.