Pretty sure it's "High Availability" in this instance...
High availability
I had to STFW to figure out what STFW meant...TIL.
You could google "HA", click in the Wikipedia link that shows all the things "HA" may refer to, and deduct that the most logical thing in the list, given the context, would be this link: https://en.wikipedia.org/wiki/High_availability.
Would it have been so hard to just type "high availability" rather than making him feel bad for being one of today's 10,000? https://xkcd.com/1053/
Why would you feel bad about not being familiar with an abbreviation?
The statement about having poor deductive logic skills was the more insulting part of the post (compared to ignorance of an initialism, which I think you are correct in thinking is insignificant).
Oddly enough, I wasn't stating that the person had poor deductive logic. I was stating the exact steps I took to find the answer myself.
Also, of note, the ever popular HAProxy Github uses and mentions stands for "High Availability Proxy".