This is a HowTo for setting up Merecat httpd with Let’s Encrypt HTTPS certificates.

The upcoming v2.32 release of Merecat supports HTTPS as well as serving more than one Internet port. This is highly useful for those who want to serve both HTTPS and HTTP content.

Update: now with support for --webroot and HTTP-01 renewal!

Getting the Source

To start with, you need the latest release of Merecat. Note, if you are reading this before Merecat v2.32 has been released you can use the latest software from the GitHub master branch. Note, you need OpenSSL and a few other packages, see the README file for details:

git clone https://github.com/troglobit/merecat.git
cd merecat/
./autogen.sh
./configure
make package
sudo dpkg -i ../merecat_2.32-1_amd64.deb

Starting Certbot

If you already have at least version v2.32 of Merecat installed you can begin the process of getting a Let’s Encrypt certificate. This HowTo use the EFF’s certbot, which is available in Ubuntu or from the Let’s Encrypt homepage:

Oups, that didn’t go as planned … well, it turns out the version of certbot in Ubuntu 18.04 lacks support for wildcard certificates. We can either go to their homepage and get the latest version, or list all the domains we need:

The Let’s Encrypt setup guide at this point recommends that we verify that automatic certificate renewal works (cronjob or systemd timer). If this doesn’t work, your certificate will expire after only six months! So let’s check that now:

It is recommended to also set up Diffie-Hellman paramaters. For this you need to genereate a site specific file:

root@example:/var/www# openssl dhparam -out certs/dhparam.pem 2048
Generating DH parameters, 2048 bit long safe prime, generator 2

This is going to take a long time
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root@example:/var/www#

The /etc/merecat.conf file for a site with a couple of virtual hosts, look like this:

## /etc/merecat.conf                                     -*-conf-unix-*-

virtual-host     = true

user-agent-deny  = "**SemrushBot**|**MJ12bot**|**DotBot**"

server default {
    port     = 80
}

server secure {
    port     = 443
    ssl {
        certfile = /etc/letsencrypt/live/example.com/fullchain.pem
        keyfile  = /etc/letsencrypt/live/example.com/privkey.pem
        dhfile   = certs/dhparam.pem
    }
}

The Merecat defaults take care of a lot of the nasty details you shouldn’t have to bother with, and unlike other web servers the virtual host setup is done in the file system rather than in the configuration file. See Merecat docs for details.

With everything set up we can fire it up:

HTTP-01 Renewal

For automatic renewal to work you need a new (July 2020) feature of Merecat, called location matching:

server default {
        port = 80
        location "/.well-known/acme-challenge/**" {
                 path = "letsencrypt/.well-known/acme-challenge/"
        }
        redirect "/**" {
                 code = 301
                 location = "https://$host$request_uri$args"
        }
}

The path must be relative to the server root directory. Use bind mounts to get /var/lib/letsencrypt into your server root. This way we can ensure certbot only writes to its own directory and cannot write to any file in the server root.

Then run certbot with the following arguments and then add all virtual hosts you want to support from Merecat:

root@example:/var/www/> certbot certonly --webroot --webroot-path /var/lib/letsencrypt --dry-run

Drop --dry-run when you’re done playing around learning all settings.

The actual renewal is set up automatically by the certbot install as a cronjob or systemd timer. Certbot uses the last known method you used to manually install/update your certs. For details on this, see the file /etc/letsencrypt/renewal/example.com.conf. (Dry runs does not change this.)

After a successful renewal you need to restart Merecat httpd to activate the new certificates. Instead of modifying the above cronjob or timer, we add the following line to /etc/letsencrypt/cli.ini:

deploy-hook = systemctl restart merecat