I've upgraded my RSS to ActivityPub converter to use an actual message queuing system (beanstalkd, in this case). https://bots.tinysubversions.com/convert/
One thing to note:
For six months this ran and mostly worked off a janky `for` loop and timer, no queue. I am extremely glad that I didn't attempt to engineer a "scalable" solution until I needed it, because I probably never would have launched it in the first place if I had (I've never implemented a message queue before).