Getting a free SSL certificate from Letsencrypt and configuring it on Nginx with automatic renewal

Posted on Sun 06 December 2015 in DevOps, HowTo, Linux • Tagged with encryption, letsencrypt, security, ssl

Finally Letsencrypt went to public beta and I really couldn't wait to use it on my VPS (where this blog is hosted). Until few days ago I was using a free SSL certificate from StartSSL. The service is nice and I'm grateful to them for this important resource they are providing for free, but it must be said that their renewal procedure isn't one of the most user friendly.

For people who don't know the service yet, Letsencrypt not only gives free SSL certificates, they also provide a command line tool that people can use to request a new certificate or to renew an existing one. This means that you don't have to worry anymore if/when your certificate expires, you can set a crontab command and have the certificate automatically renewed for you.

Client installation

To request a SSL certificate you need to install their command line utility. Unless it has already been packaged for your distribution, for the moment it's much easier to get it from git as they explain in their installation instructions:

git clone https://github.com/letsencrypt/letsencrypt
cd letsencrypt
./letsencrypt-auto

Getting the SSL certificate

There are a few different options available to request a certificate, but the easiest one is to use the --webroot option, specifying the document root of your website so that the client will be able to put there a verification (temporary) file that will be served to the remote service and used as verification method. In my case I only needed this command:

./letsencrypt-auto certonly --webroot -w /var/www/andreagrandi.it/ -d www.andreagrandi.it -d andreagrandi.it --email [email protected] --renew-by-default --agree-tos

Please note that I had to specify both www.andreagrandi.it and andreagrandi.it as domains, otherwise it would have been invalid when requesting just andreagrandi.it resources.

Configuration files and certificates installation

The command above will save all the configuration under /etc/letsencrypt/ and all the generated certificates under /etc/letsencrypt/live/www.andreagrandi.it/*.pem (all the *.pem files here are symbolic links to the current certificate). If you are using Nginx the only files you need are fullchain.pem and privkey.pem and you can set them in your Nginx configuration using these two parameters:

ssl_certificate /etc/letsencrypt/live/www.andreagrandi.it/fullchain.pem;
ssl_certificate_key /etc/letsencrypt/live/www.andreagrandi.it/privkey.pem;

In case you want to have a look at my full Nginx configuration file, as reference, you can find it here https://gist.github.com/andreagrandi/8b194c99cd3e77fdb5a8

Automatic renewal

The last thing to be configured is a crontab rule to call the script every... 2 months. Why 2 months? Letsencrypt SSL certificates expire in 3 months. Usually SSL certificates are valid at least for 1 year, but Letsencrypt decided to make it 3 months to incentivate the automation of the renewal. I set it to 2 months, so if anything goes wrong I still have plenty of time to do it manually. To edit crontab for root user execute crontab -e and add this line:

0 3 1 */2 * /root/letsencrypt/letsencrypt-auto certonly --webroot -w /var/www/andreagrandi.it/ -d www.andreagrandi.it -d andreagrandi.it --email [email protected] --renew-by-default --agree-tos && service nginx reload

Just a final note. You may have noticed that this website presents an SSL certificate issued by COMODO. That's because I have CloudFlare in front of my website and that's how their SSL strict option works (at least for free plans).