OpenVPN in a Docker container on CentOS 7 with SystemD support

September 10, 2015

In this guide, we will set up Docker on a Digital Ocean CentOS 7 droplet, then set up OpenVPN. We’ll also discuss how to create a custom SystemD service file so that we can manage our container with systemctl commands.

VPNs (virtual private networks) are a great way to secure your internet traffic over untrusted connections. It can provide easy access to your home network file server or other machines that you don’t want to expose to the internet directly. Also, you can use it to circumvent blocked sites or services on a company network, or it can be used as a proxy to access restricted content in your country (like Hulu or Netflix).

Docker allows you to easily deploy and manage Linux containers: isolated, virtualized environments. Their isolation makes them secure and easy to manage, especially for developers who can develop their container, without worrying about which distro or even OS it will be deployed to.

This guide assumes you already have a CentOS 7 server set up. I recommend using Digital Ocean, but any provider which gives you root access will work as well. This guide should also work with any distribution that uses SystemD. I liked the set up so much, that I implemented it on my home Arch server as well.


First, let’s install docker:

sudo yum -y update
sudo yum -y install docker docker-registry

Once that’s done, we’ll start Docker and then enable it to start at boot:

sudo systemctl start docker.service
sudo systemctl enable docker.service

If you don’t want to have to type sudo every time you use the docker command, then you’ll have to add your user to the group ‘docker’. Do so with:

sudo usermod -aG docker $USER
newgrp docker

The second command will make your current session aware of your new group.


Now that Docker is up and running, we’ll need to set up busybox and OpenVPN. busybox is a super minimal docker image designed for embedded systems. We just want it for its small footprint. All we’re running is a VPN, so theres no need for extra fluff.

Get it set up with:

sudo docker run --name dvpn-data -v /etc/openvpn busybox
docker run --volumes-from dvpn-data --rm kylemanna/openvpn ovpn_genconfig -u udp://$DOMAIN:1194
docker run --volumes-from dvpn-data --rm -it kylemanna/openvpn ovpn_initpki

The first command pulls the busybox image and creates a new container called ‘dvpn-data’. The second command starts a container that will hold the configuration files and certificates. Replace $DOMAIN with the IP or domain of your server. Take note that port 1194 will need to be opened in your firewall. The thrid command will generate Diffe-Hellman parameters. It will take a long time so just be patient.

To open the required port in firewalld, issue the following command:

sudo firewall-cmd --permanent --zone=public --add-port=1194/udp

Now we need to create the credentials that will allow your client to connect to the VPN.

sudo docker run --volumes-from dvpn-data --rm -it kylemanna/openvpn easyrsa build-client-full $CONNECTION_NAME nopass
sudo docker run --volumes-from dvpn-data --rm kylemanna/openvpn ovpn_getclient $CONNECTION_NAME > $CONNECTION_NAME.ovpn

Replace $CONNECTION_NAME with whatever you want to call your VPN connection. I named mine after my server name. You will be asked to create a password during the process, just pick one. It will take a while to do some crypto stuff, but eventually you’ll get an ovpn file in your current director. This is what will allow you to add the connection to your client. You will need to securely move this to the machine that will be connecting to your vpn. rsync or scp are good options. You could even use a usb thumb drive.

Since the first machine I used this VPN for was a Mac I use at work, I chose Tunnelblick for my client. After it’s installed, double clicking on the ovpn file is all the set up that was needed to add the connection to Tunnelblick on Mac. Consult your client’s documentation if this doesn’t work for you.

Manage your new container with SystemD

Now that we’ve got all of the docker stuff out of the way, let’s create a custom systemd service file so we can manage our new container with the systemctl command. SystemD service files are like init or Upstart scripts, but can be more robust and even take the place of Cron.

In CentOS 7 and Arch, these files are kept in /etc/systemd/system/ so we’ll put our’s their too. Fire up your text editor of choice, for me it’s sudo vim /etc/systemd/system/dvpn.service, and paste in the following:

Description=OpenVPN Docker Container

ExecStart=/usr/bin/docker run --name vpn --volumes-from dvpn-data --rm -p 1194:1194/udp --cap-add=NET_ADMIN kylemanna/openvpn
ExecReload=/usr/bin/docker stop && /usr/bin/docker run --name vpn --volumes-from dvpn-data --rm -p 1194:1194/udp --cap-add=NET_ADMIN kylemanna/openvpn
ExecStop=/usr/bin/docker stop vpn


There’s a lot going on here, so let’s break it down. The stuff in the [Unit] section is straigtforward enough. We give our service file an arbitrary description. The Requires=docker.service and After=docker.service mean that this service won’t start until after the docker service has started.

The Restart=always means that our service will restart if it fails. The ExecStart= tells systemd what to run when we start the service. Let’s break this command down further, to help you understand what’s going on here:

You can find more info about the docker run command in the Docker documentation, it has tons of options. Of course, you could just check the man page for it, with man docker run.

Finally, the [Install] section basically allows us to enable the service to be enabled to start at boot. You can read more about systemd service files in this excellent tutorial: Understanding Systemd Units and Unit Files.

Now that our service is created we can start it and enable it to load at boot with:

sudo systemctl start dvpn.service
sudo systemctl enable dvpn.service

You can also check its status with sudo systemctl status dvpn.service

And that’s it! You now have a SystemD managed, Docker controlled, OpenVPN set up. Enjoy!

UPDATE:I tried following my own guide to create a vpn on my home Arch Linux rig and ran into some problems. You might get iptables errors when attempting to start the dvpn service file created above.

└─[13:19]$ docker run --name vpn --volumes-from ovpn-data --rm -p 1194:1194/udp --cap-add=NET_ADMIN kylemanna/openvpn
Error response from daemon: Cannot start container d8afcbc7069b0530893779c9abf4d10aa73ab53f820c310a8baf2b956f79877c: failed to create endpoint vpn on network bridge: iptables failed: iptables --wait -t nat -A DOCKER -p udp -d 0/0 --dport 1194 -j DNAT --to-destination ! -i docker0: iptables: No chain/target/match by that name.
 (exit status 1)

It is possibly due to either the xt_conntrack kernel module not loading or because you simply need to restart the firewalld and docker daemons to reload the iptables rules. Additional info can be found here. Try restarting the daemons first with:

sudo systemctl restart firewalld
sudo systemctl restart docker

If that doesn’t work, try loading the kernel module:

sudo modprobe xt_conntrack


Secure Your WordPress With a Free SSL Certificate in Apache on CentOS 7

July 3, 2015

It is simple enough to use a self-signed certificate to encrypt traffic to your site with SSL, but if you have a WordPress blog or any site that might see lots of visitors, then a self-signed certificate is not an option: How many average users are going to proceed to your site with a warning from their Web browser about an untrusted connection? This guide will show you start to finish how to get a free SSL certificate from StartSSL, install it on your server, configure apache, and set up WordPress to use https.

All of the information I’m using is from these guides:

If you get stuck, it might help to reference one of these guides. My set up is a CentOS 7 Digital Ocean droplet with apache and WordPress, but a lot of these steps should work for other distributions. Also, keep in mind that the free certificate offered by StartSSL is for non-commercial use only.

What you’ll need


Open up Chrome and head to Click on “Express Signup,” fill out the forms and hit continue. Check your email for the verification code. Click the link in the e-mail and you will be asked to generate a private key. Choose “High” for the grade. Once it’s done, click “Install” and Chrome will present you with a pop-up that says it has been successfully installed.

This is not your SSL certificate, it’s just a key that you will use to log in to the StartSSL Web site. Click on “Control Panel” and then “Authenticate.” Chrome will give you a pop-up to authenticate with the site.

Validate your domain

Once you’re in the Control Panel, click on the Validations Wizard tab and select “Domain Name Validation” from the drop-down menu. Choose whichever e-mail you have access to (like

If you’re using Google Apps for your e-mail provider, you can just create a group called webmaster and give it public access permissions to post to the group. Add yourself to the group and you will get any messages sent to This is any easy way to get extra addresses forwarding to your main Google Apps account without creating another user.

Check that whatever account you’re using for the validation e-mail and paste in the code.

Create the Certificate

In the Control Panel, click on the “Certificates Wizard” tab. Select “Web Server SSL/TLS Certificate” from the drop-down menu. Hit continue and enter a strong password. You’ll get a text box that contains your key. Copy its contents into your text editor of choice and save the file as ssl.key.

Hit continue and select your recently verified domain. Choose a sub-domain on the next screen. You probably want to pick ‘www’, but it’s up to you. Hit continue and you’ll get another text box, this time containing your certificate. Copy it to your text editor and save it as ssl.crt.

Download the CAs

Click on “Toolbox,” and download the StartCom Root CA and the StartSSL’s Class 1 Intermediate Server CA. Just right-click on the links with those names and hit save as.

Now we need to unencrypt your your private key so that your sever can use it. Do so with:

openssl rsa -in ssl.key -out private.key

You should now have 5 files:


Note: the private.key file is the unencrypted version of your private key. Make certain that no one has access to it and that you delete it from your local machine once you upload it to the server. It isn’t necessary to upload the ssl.key file to your server. Let’s upload the ones we do need though, using scp:

scp -p 2222 {ca.pem,private.key,,ssl.crt}

In this example, the ssh listening port is 2222, change it to whatever your port is. You can also specify a different destination directory by changing /home/user to whatever you want.


SSH into your server and let’s get it set up.

$ sudo yum install -y mod_ssl
$ sudo mkdir /etc/httpd/ssl
$ sudo mv {ca.pem,private.key,,ssl.crt} /etc/httpd/ssl
$ sudo nano /etc/httpd/conf.d/ssl.conf

The first command will install the ssl module for apache, the second creates a directory for your certificate to live in. The third command will move all of your certificate files to your newly created ssl directory. The last will open up the ssl configuration file for apache. Look for this line:

<VirtualHost _default_:443>

Uncomment (delete the # at the beginning of the line) the DocumentRoot and ServerName lines and change to whatever your domain is. It is important that this match what you entered when you created the certificate.

Uncomment these lines as well and change the location of the files to match what’s shown here:

SSLCertificateFile /etc/apache2/ssl/ssl.crt                           
SSLCertificateKeyFile /etc/apache2/ssl/private.key                        
SSLCertificateChainFile /etc/apache2/ssl/

Once you’re done, save and close the ssl.conf file and open up your site’s configuration file:

$ sudo vim /etc/httpd/sites-enabled/

And add these lines before the closing :

RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI}

This will force https for the whole site, so that even if users don’t type out https:// before your address, they will still be protected.

Restart the apache server:

$ sudo systemctl restart httpd

Test that it works by going to You should see a little lock in the address bar. If you get an Untrusted Connection error, then you probably forgot to change the location of the certificate files from the defaults in the ssl.conf file. If you get a lock symbol, but with a triangular alert symbol, then you’ve got yourself a mixed content warning. No big deal, we’ll fix that in the next step.


Log in to your WordPress admin portal and click on “Settings,” and change the “WordPress Address (URL)” from to Make the same change to the “Site Address (URL)” field as well.

If you’ve got the Mixed Content warning, then you’ve got some work to do. This warning basically means that your Web browser has detected some content on the page that is being fetched with plain old http, meaning it’s not encrypted and secure. This could mean anything, but images you’ve added to posts is a great place to start. Take a look at one of your posts with images and view it in text mode. Scroll down to where your image is and check the html, if it looks like this:<img src="" ... then that’s probably the problem.

There are a number of ways to fix this. If you have a new site, then you can just click through your posts and add an ‘s’ after http to all of your image tags. If you have hundreds or more images, this could get tedious. This guide: Moving to HTTPS on WordPress has some SQL kung fu that might be able to automate the process for you. <iframe> or <link> tags could also be causing the problem if they are calling http. This stackoverflow post has some more info as well.

Keep an eye out for mixed content warnings on other pages, but otherwise you should be done!