I just reduced 14 Let's Encrypt certificates down to 2. This is possible because the free service went live for wildcard certs. This has great implications for people who use the WordPress Multisite feature or routinely light up new virtual hosts in the same domain.
You can read Let's Encrypt's understated announcement here.
On my VPS I run Ubuntu 17.10 and it has a version of certbot that you can get from the official repo. Sadly, it's the 0.21 release and wildcard certs need ACME v2 support and that's only in release 0.22 and greater.
Here's what I did
On the command line I cloned cerbot from Github.
git clone https://github.com/certbot/certbot.git
You'll see something like so. On my main box it asked if I'm OK with installing more Python packages. A quick installation of those dependencies and I was ready to go.
Press c to cancel. You want wildcard not single hostname certs. Now type this as one line.
sudo ./certbot-auto certonly --manual --server https://acme-v02.api.letsencrypt.org/directory
The server argument is the important one and points to the new V2 API. I could modify the configuration but I'd have to remember what/where I did that. This is easier for me. Certs generated using the V1 API will work and renew with the new one so there's no worries there. The manual argument prompts you through the steps and ask what domains to use.
Normally this is not a manual process. But for the ACME V2 API, an additional check is required and I don't have a certbot plugin to interface with my DNS provider.
When prompted for the domain name I used "*.dembowski.net dembowski.net" and was instructed to create a DNS TXT record for _acme-challenge.dembowski.net as well as a file in dembowski.net/.well-known/acme-challenge/ with a generated name and content.
If you can put that file on the right web server, if you can update your DNS, then you're considered legitimate. Just make sure you wait for DNS to propagate first before proceeding. You can check if it has (at least for Google) using this link.
I have Namecheap and after a quick visit to that dashboard, I waited for the new TXT record to populate, I created that special file and hit enter.
POOF! My server was validated and the certificates were placed in /etc/letsencrypt and a few minutes later my many hosts were updated to point to that new wildcard cert. I repeated this for my other domain and I'm good.
WordPress Multisite and wildcard certs
If you are running multisite then this simplifies your life tremendously. You can and should have one virtual host for your installation. In my case, they're underneath *.dembowski.net.
In my nginx configuration, I modified the server_name line to add *.dembowski.net and I removed the other vhosts files. They were pointing to the same directory for WordPress and they're not needed anymore.
Less is more. I've been waiting for this since they announced it and lighting up new web server instances while maintaining transport level encryption is such a good thing. Let's Encrypt continues to make the web a more secure place.