Let's Encrypt and IPv6
I’m using Let’s Encrypt as Certificate Authority on this and many other sites. I like it, as it allows me to automate certificate creation and renewals, however I also have some monitoring making sure everything works as expected.
I recently got a few alerts as some certificates weren’t renewed as expected. I figured nothing had changed on the server setup and there was renewal happening for a few days, I started looking into it and found the issue why the renewal was failing, so here’s the story.