This post is a follow up to my previous one Automating SSL Certificates using Nginx & LetsEncrypt. This time we’ll be generating SSL certificates for intranet and non-public networks.
Before we get started, you’ll want to make sure that the following items are true.
- You must use a real/purchased domain. Reserved domains/TLD’s like
*.localwill never work.
- You must have an external DNS provider that has an API.
- If your DNS provider doesn’t have an API, you can use cloud flare.com for free.
- You must have python 2.6+ installed
The first step is to install a Letsencrypt client. The official client is a bit bloated and complicated to setup. I prefer to use the dehydrated client instead as its code is easier to understand, has few dependencies and its incredibly simple to automate.
# install dehydrated dependencies (most should already be installed) apt-get install -y openssl curl sed grep mktemp git # install dehydrated into /srv/dehydrated git clone https://github.com/lukas2511/dehydrated.git /srv/dehydrated
Dehydrated requires some configuration, but not much, the defaults work out of the box. That means that all you need to do is
- create a domains.txt file with the url(s) of the site(s) you’re generating ssl certificates for
Here’s how we can do that.
# First we need to make the client executable chmod +x /srv/dehydrated/dehydrated # Then we need to specify the intranet/private domain echo "test.intranet.example.com" > /srv/dehydrated/domains.txt
Next we’re going to install the Lexicon library. Lexicon provides a way to manipulate DNS records on multiple DNS providers in a standardized way.
# install python requests library dependencies apt-get install -y build-essential python-dev curl libffi-dev libssl-dev pip install requests[security] pip install dns-lexicon
The Lexicon library lets you automatically configure your DNS provider using Letsencrypt DNS challenges without having to deal with creating API calls yourself. Its perfect for generating internal/intranet SSL certs.
Dehydrated requires a hook file to complete
dns-01 challenges. The Lexicon repo has an example one that wires up the
clean_challenge calls to Lexicon commands.
curl -O https://raw.githubusercontent.com/AnalogJ/lexicon/master/examples/dehydrated.default.sh /srv/dehydrated chmod +x /srv/dehydrated/dehydrated.default.sh
The only information that Lexicon requires is:
- authentication information such as username/password or token.
- In general your API token should be availble in your DNS provider’s account settings page.
- provider name
We can pass all that information to Lexicon by setting a handful of environmental variables. If don’t want to do that, you can modify the hook file and add the
--auth-password parameters to all
#If our DNS provider is cloudflare export PROVIDER=cloudflare export LEXICON_CLOUDFLARE_USERNAMEemail@example.com export LEXICON_CLOUDFLARE_TOKEN=234dcef90c3d9aa0eb6798e16bdc1e4b
Now that we’ve finished configuring everything, it’s time to generate the certificates. Its as simple as:
# Lets generate the Letsencrypt SSL certificates /srv/dehydrated/dehydrated --cron --hook /srv/dehydrated/dehydrated.default.sh --challenge dns-01
Our certificates will be available in the following folder:
At this point we have working Letsencrypt SSL certificates for an internal/intranet domain that’s not accessible on the public internet.
I’ve written an example Dockerfile that you can reference if you’re curious. Just make sure to use
docker run -e "PROVIDER=cloudflare" -e .. to set the environmental variables that you need.
If you’re wondering how to automate this whole process, check out my previous post: Automating SSL Certificates using Nginx & LetsEncrypt