I've integrated letsencrypt into propellor today.

I'm using the reference letsencrypt client. While I've seen complaints that it has a lot of dependencies and is too complicated, it seemed to only need to pull in a few packages, and use only a few megabytes of disk space, and it has fewer options than ls does. So seems fine. (Although it would be nice to have some alternatives packaged in Debian.)

I ended up implementing this:

letsEncrypt :: AgreeTOS -> Domain -> WebRoot -> Property NoInfo

This property just makes the certificate available, it does not configure the web server to use it. This avoids relying on the letsencrypt client's apache config munging, which is probably useful for many people, but not those of us using configuration management systems. And so avoids most of the complicated magic that the letsencrypt client has a reputation for.

Instead, any property that wants to use the certificate can just use leteencrypt to get it and set up the server when it makes a change to the certificate:

letsEncrypt (LetsEncrypt.AgreeTOS (Just "me@my.domain")) "example.com" "/var/www"
    `onChange` setupthewebserver

(Took me a while to notice I could use onChange like that, and so divorce the cert generation/renewal from the server setup. onChange is awesome! This blog post has been updated accordingly.)

In practice, the http site has to be brought up first, and then letsencrypt run, and then the cert installed and the https site brought up using it. That dance is automated by this property:

Apache.httpsVirtualHost "example.com" "/var/www"
    (LetsEncrypt.AgreeTOS (Just "me@my.domain"))

That's about as simple a configuration as I can imagine for such a website!

The two parts of letsencrypt that are complicated are not the fault of the client really. Those are renewal and rate limiting.

I'm currently rate limited for the next week because I asked letsencrypt for several certificates for a domain, as I was learning how to use it and integrating it into propellor. So I've not quite managed to fully test everything. That's annoying. I also worry that rate limiting could hit at an inopportune time once I'm relying on letsencrypt. It's especially problimatic that it only allows 5 certs for subdomains of a given domain per week. What if I use a lot of subdomains?

Renewal is complicated mostly because there's no good way to test it. You set up your cron job, or whatever, and wait three months, and hopefully it worked. Just as likely, you got something wrong, and your website breaks. Maybe letsencrypt could offer certificates that will only last an hour, or a day, for use when testing renewal.

Also, what if something goes wrong with renewal? Perhaps letsencrypt.org is not available when your certificate needs to be renewed.

What I've done in propellor to handle renewal is, it runs letsencrypt every time, with the --keep-until-expiring option. If this fails, propellor will report a failure. As long as propellor is run periodically by a cron job, this should result in multiple failure reports being sent (for 30 days I think) before a cert expires without getting renewed. But, I have not been able to test this.