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07 Mar 2016, 08:37

Let's Encrypt - setting up automated certificate renewals

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let's encrypt

Not too long ago, Let’s Encrypt launched a free CA to enable website owners to easily generate their own signed certificates from the command line on their server. It integrates with popular web servers like Apache and NGINX to make the validation step easier. However, the certificates are only valid for 3 months, as opposed to the 1 year that is more typical. They’ll send an email when your certificate is close to expiring, but that’s not always idea. The good news is that since this is a command line tool, it can be easily written into a cron job to run periodically.

The current release, 0.4.2, seems to work reasonably well for scripted renewals. There are a couple notes for issues that I ran into, at least with this version. First, here’s the general command that I use for renewals:

./letsencrypt/letsencrypt-auto certonly --no-self-upgrade --apache --force-renew --renew-by-default --agree-tos -nvv --email admin@example.com -d example.com,www.example.com >> /var/log/letsencrypt/renew.log

That’s great when you have a simple site, with sub-domains that all point to one set of content, and one vhost entry (per port). If you have a couple of different subdomains that relate to different sets of content, something like this:

./letsencrypt/letsencrypt-auto certonly --no-self-upgrade --apache --force-renew --renew-by-default --agree-tos -nvv --email admin@example.com -d example.com,www.example.com,app.example.com >> /var/log/letsencrypt/renew.log

Where app.example.com in the above example relates to a different vhost. In this case, you’ll need to break the vhosts into separate files. See the below examples.

Vhost for example.com and www.example.com:

<VirtualHost *:80>
    ServerAdmin admin@example.com
    ServerName example.com
    ServerAlias www.example.com
    DocumentRoot "/var/www/example/"
    <Directory "/var/www/example/">
        DirectoryIndex index.html
        RewriteEngine On
        RewriteOptions Inherit
        AllowOverride All
        Order Deny,Allow
        Allow from all
        Require all granted
    </Directory>
</VirtualHost>

<VirtualHost *:443>
    ServerAdmin admin@example.com   
    ServerName example.com
    ServerAlias www.example.com  
    DocumentRoot "/var/www/example/"
    <Directory "/var/www/example/">
        AllowOverride all
        Options -MultiViews +Indexes +FollowSymLinks
        DirectoryIndex index.html index.htm
        Order Deny,Allow
        Allow from all
        AllowOverride All
        Require all granted
        DirectoryIndex index.html index.php index.phtml index.htm
    </Directory>

    ErrorLog "/var/log/httpd/example.com-error_log"
    CustomLog "/var/log/httpd/example.com-access_log" common

    SSLEngine on

    SSLCertificateFile /etc/letsencrypt/live/example.com/fullchain.pem
    SSLCertificateKeyFile /etc/letsencrypt/live/example.com/privkey.pem
</VirtualHost>

Vhost for app.example.com:

<VirtualHost *:80>
    ServerAdmin admin@example.com
    ServerName app.example.com
    DocumentRoot "/var/www/example-app/"
    <Directory "/var/www/example-app/">
        DirectoryIndex index.html
        RewriteEngine On
        RewriteOptions Inherit
        AllowOverride All
        Order Deny,Allow
        Allow from all
        Require all granted
    </Directory>
</VirtualHost>

<VirtualHost *:443>
    ServerAdmin admin@example.com   
    ServerName app.example.com
    DocumentRoot "/var/www/example-app/"
    <Directory "/var/www/example-app/">
        AllowOverride all
        Options -MultiViews +Indexes +FollowSymLinks
        DirectoryIndex index.html index.htm
        Order Deny,Allow
        Allow from all
        AllowOverride All
        Require all granted
        DirectoryIndex index.html index.php index.phtml index.htm
    </Directory>

    ErrorLog "/var/log/httpd/example-app.com-error_log"
    CustomLog "/var/log/httpd/example-app.com-access_log" common

    SSLEngine on

    SSLCertificateFile /etc/letsencrypt/live/example.com/fullchain.pem
    SSLCertificateKeyFile /etc/letsencrypt/live/example.com/privkey.pem
</VirtualHost>

Then, I created a script that handles a couple of different renewals, and at the end, a command to reload apache configs, called updateCerts.sh:

#!/bin/bash

./letsencrypt/letsencrypt-auto certonly --no-self-upgrade --apache --force-renew --renew-by-default --agree-tos -nvv --email admin@example.com -d example.com,www.example.com,app.example.com >> /var/log/letsencrypt/renew.log
./letsencrypt/letsencrypt-auto certonly --no-self-upgrade --apache --force-renew --renew-by-default --agree-tos -nvv --email admin@thing.com -d thing.com,www.thing.com,files.thing.com >> /var/log/letsencrypt/renew.log

apachectl graceful

Then, I added this to the root user’s crontab:

# m h  dom mon dow   command
0 4  *   *   1     /home/user/updateCerts.sh

Cron is supposed to run this script once a week, and we’ll have logs at /var/log/letsencrypt/renew.log.

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