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.

HTTPS, SSL, TLS - What it does

While surfing the net, you often come across web agencies how promote SSL-certificates (or TLS security) on their products - or their ability to create “secure web applications” with SSL. Most users know HTTPS/SSL/TLS as the little lock, that promises “security” when visiting a page - but what kind of security it actually provides is rarely explained - and far worse often misunderstood. The while SSL is the popular name (and as it was once known) and HTTPS usually is the way users sees it (as part of a URL in a browser) - the correct name is TLS a short for Transport Layer Security.