It is super nice, isn't it? I am so amazed how awesome people in the open source community are.

As for the scale question: The server is already tuned for scale: https://ntfy.sh/docs/config/#tuning-for-scale

If you have any more ideas of what nobs to turn, let me know.

I appreciate the dogged pursuit of efficiency, but spending a lot of time optimizing for the current scale and getting costs from $24 per month to $10 per month (or whatever) is likely wasted time if this grows significantly. You have to be able to recognize there’s a lower bound where your costs are low enough it doesn’t matter and even saving 75% isn’t worth thr effort. The author has obviously drawn that line somewhere above $24 per month and that’s perfectly reasonable.

That's a good point. I guess many of us were suggesting cheaper VPS because we assumed this is a new project, just launched. (Most inexperienced developers / start-ups tend to over provision). With current hosting technologies, it is quite easy to scale with need, with minimum downtime, so it makes sense to start with the minimum server requirement and then go for a powerful server as required. This give you valuable data on the bottlenecks (where you can do future optimizations), as you scale, while you temporarily fix the issue with more money (by requisitioning better servers) as you work out the cost-benefit analysis (as you did) of spending money on optimising vs server upgrade.