I am pretty sure that this is the thread that introduced me to it: https://news.ycombinator.com/item?id=10681851

Unfortunately, web.archive.org didn't grab an https version of my main site from around that period. My oldest server build script in my current collection does have the following note in it:

    **Get the current version of dehydrated from https://github.com/dehydrated-io/dehydrated **
    (Dehydrated was previously found at https://github.com/lukas2511/dehydrated)

But yeah, circa 2015 - 2016 should be about right. I had been hosting stuff for clients since... phew, 2009? So LetsEncrypt was something I wanted to adopt pretty early, because back then certificate renewals were kind of annoying and often not free, but I also didn't want to load whatever the popular ACME client was at the time. Then this post popped up, and it was exactly what I had been looking for, and would have started using it soon after.

edit: my Linode account has been continuously active since October 2009, though it only has a few small legacy services on it now. I started that account specifically for hosting mail and web services for clients I had at the time. So, yeah, my memory seems accurate enough.