Introduction

This tutorial will show you how to set up a TLS/SSL certificate from Let's Encrypt on a Debian 8 server running Apache as a web server. We will also cover how to automate the certificate renewal process using a cron job.

SSL certificates are used within web servers to encrypt the traffic between the server and client, providing extra security for users accessing your application. Let's Encrypt provides an easy way to obtain and install trusted certificates for free.

Prerequisites

In order to complete this guide, you will need a Debian 8 server with a non-root sudo user for administrative tasks. You can set up a user with the appropriate permissions by following our Debian 8 initial server setup guide.

You must own or control the registered domain name that you wish to use the certificate with. If you do not already have a registered domain name, you may register one with one of the many domain name registrars out there (e.g. Namecheap, GoDaddy, etc.).

If you haven't already, be sure to create an A Record that points your domain to the public IP address of your server (if you are using DigitalOcean's DNS, you can follow this guide). This is required because of how Let's Encrypt validates that you own the domain it is issuing a certificate for. For example, if you want to obtain a certificate for example.com, that domain must resolve to your server for the validation process to work. Our setup will use example.com and www.example.com as the domain names, so both DNS records are required.

When you are ready to move on, log into your server using your sudo account.

Step 1: Install Certbot, the Let's Encrypt Client

The first step to using Let's Encrypt to obtain an SSL certificate is to install the certbot Let's Encrypt client on your server.

The certbot package was not available when Debian 8 was released. To access the certbot package, we will have to enable the Jessie backports repository on our server. This repository can be used to install more recent versions of software than the ones included in the stable repositories.

Add the backports repository to your server by typing:

echo 'deb http://ftp.debian.org/debian jessie-backports main' | sudo tee /etc/apt/sources.list.d/backports.list

After adding the new repository, update the apt package index to download information about the new packages:

sudo apt-get update

Once the repository is updated, you can install the python-certbot-apache package, which pulls in certbot, by targeting the backports repository:

sudo apt-get install python-certbot-apache -t jessie-backports

The certbot client should now be ready to use.

Step 2: Set Up the Apache ServerName and ServerAlias

It is possible to pass the domains that we wish to secure as arguments when calling the certbot utility. However, certbot can also read these from the Apache configuration itself. Since it is good practice to always be explicit about the domains your server should respond to, we will set the ServerName and ServerAlias in the Apache configuration directly.

When we installed the python-certbot-apache service, Apache was installed if it wasn't already present on the system. Open the default Apache Virtual Host file so that we can explicitly set our domain names:

sudo nano /etc/apache2/sites-available/000-default.conf

Inside, within the Virtual Host block, add or uncomment the ServerName directive and set it to your primary domain name. Any alternative domain names that this server should also respond to can be added using a ServerAlias directive.

For our example, we are using example.com as our canonical name and www.example.com as an alias. When we set these directives, it will look like this:

<VirtualHost *:80>
    . . .
    ServerName example.com
    ServerAlias www.example.com
    . . .
</VirtualHost>

When you are finished, save and close the file by holding CTRL and pressing X. Type Y and hit Enter to save the file.

Check the configuration file to catch any syntax errors that may have been introduced by your changes:

sudo apache2ctl configtest

Look for this line in the output:

Output
Syntax OK

If the file passed the syntax test, restart your Apache service to implement your changes:

sudo systemctl restart apache2

Now that Apache is configured with your domain names, we can use certbot to obtain our SSL certificates.

Step 3: Adjusting the Firewall

If you have a firewall enabled, you'll need to adjust the settings to allow for SSL traffic. The required procedure depends on the firewall software you are using. If you do not have a firewall configured currently, feel free to skip forward.

UFW

If you are using ufw, you can see the current setting by typing:

sudo ufw status

It may look like this, meaning that only SSH traffic is allowed to the web server:

Output
Status: active

To                         Action      From
--                         ------      ----
SSH                        ALLOW       Anywhere
SSH (v6)                   ALLOW       Anywhere (v6)

To additionally let in HTTP and HTTPS traffic, we can allow the "WWW Full" application profile:

sudo ufw allow 'WWW Full'

Your status should look like this now:

sudo ufw status

Output
Status: active

To                         Action      From
--                         ------      ----
SSH                        ALLOW       Anywhere
WWW Full                   ALLOW       Anywhere
SSH (v6)                   ALLOW       Anywhere (v6)
WWW Full (v6)              ALLOW       Anywhere (v6)

HTTP and HTTPS requests should now be accepted by your server.

IPTables

If you are using iptables, you can see the current rules by typing:

sudo iptables -S

If you have any rules enabled, they will be displayed. An example configuration might look like this:

Output
-P INPUT DROP
-P FORWARD ACCEPT
-P OUTPUT ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 80 -j ACCEPT

The commands needed to open SSL traffic will depend on your current rules. For a basic rule set like the one above, you can add SSL access by typing:

sudo iptables -I INPUT -p tcp --dport 443 -j ACCEPT

If we look at the firewall rules again, we should see the new rule:

sudo iptables -S

Output
-P INPUT DROP
-P FORWARD ACCEPT
-P OUTPUT ACCEPT
-A INPUT -p tcp -m tcp --dport 443 -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 80 -j ACCEPT

If you are using a program to automatically apply iptables rules at boot, you will want to make sure that you update your configuration with the new rule.

Step 4: Set Up the SSL Certificate

Generating the SSL Certificate for Apache using the Let's Encrypt client is quite straightforward. The client will automatically obtain and install a new SSL certificate that is valid for the domains in our Apache configuration.

To execute the interactive installation and obtain a certificate for all of the domains defined in your Apache configuration, type:

sudo certbot --apache

The certbot utility will evaluate your Apache configuration to find the domains that should be covered with the requested certificate. You will be able to deselect any defined domains that you do not wish to be covered under the certificate.

You will be presented with a step-by-step guide to customize your certificate options. You will be asked to provide an email address for lost key recovery and notices, and you will be able to choose between enabling both http and https access or forcing all requests to redirect to https. It is usually safest to require https, unless you have a specific need for unencrypted http traffic.

When the installation is finished, you should be able to find the generated certificate files at /etc/letsencrypt/live. You can verify the status of your SSL certificate with the following link (don't forget to replace example.com with your domain):

https://www.ssllabs.com/ssltest/analyze.html?d=example.com&latest

The test may take a few minutes to complete. You should now be able to access your website using a https prefix.

Step 5: Set Up Auto Renewal

Let's Encrypt certificates are valid for 90 days, but it's recommended that you renew the certificates every 60 days to allow a margin of error. The certbot client has a renew command that automatically checks the currently installed certificates and tries to renew them if they are less than 30 days away from the expiration date.

To trigger the renewal process for all installed domains, you should run:

sudo certbot renew

Because we recently installed the certificate, the command will only check for the expiration date and print a message informing that the certificate is not due to renewal yet. The output should look similar to this:

Output
Saving debug log to /var/log/letsencrypt/letsencrypt.log

-------------------------------------------------------------------------------
Processing /etc/letsencrypt/renewal/example.com.conf
-------------------------------------------------------------------------------
Cert not yet due for renewal

The following certs are not due for renewal yet:
  /etc/letsencrypt/live/example.com/fullchain.pem (skipped)
No renewals were attempted.

Notice that if you created a bundled certificate with multiple domains, only the base domain name will be shown in the output, but the renewal should be valid for all domains included in this certificate.

A practical way to ensure your certificates won't get outdated is to create a cron job that will periodically execute the automatic renewal command for you. Since the renewal first checks for the expiration date and only executes the renewal if the certificate is less than 30 days away from expiration, it is safe to create a cron job that runs every week or even every day, for instance.

Let's edit the crontab to create a new job that will run the renewal command every week. To edit the crontab for the root user, run:

sudo crontab -e

You may be prompted to select an editor:

Output
no crontab for root - using an empty one

Select an editor.  To change later, run 'select-editor'.
  1. /bin/nano        <---- easiest
  2. /usr/bin/vim.basic
  3. /usr/bin/vim.tiny

Choose 1-3 [1]:

Unless you're more comfortable with vim, press Enter to use nano, the default.

Include the following content at the end of the crontab, all in one line:

crontab
. . .
30 2 * * 1 /usr/bin/certbot renew >> /var/log/le-renew.log

Save and exit. This will create a new cron job that will execute the letsencrypt-auto renew command every Monday at 2:30 am. The output produced by the command will be piped to a log file located at /var/log/le-renewal.log.

For more information on how to create and schedule cron jobs, you can check our How to Use Cron to Automate Tasks in a VPS guide.

Conclusion

In this guide, we saw how to install a free SSL certificate from Let's Encrypt in order to secure a website hosted with Apache. We recommend that you check the official Let's Encrypt blog for important updates from time to time.