I can't speak to the technical aspects here (I'm only familiar with nextjs not rails, so it's unclear to me how much of the article is just a reflection of the author's own comfortability with rails or a reflection of a more technically suitable architecture). But I do find it really weird that a company which apparently has multiple software engineers is worried about infrastructure costs amounting to less than $1k a month... Seems penny-wise pound-foolish to be worried about hosting bills.
We have one developer (me) and we're bootstrapped and not yet profitable. That means I'm paying the difference every month in hosting and working for free. The site makes it look like we have a lot more together than we are.
Was using TeamCity, then dropped some moving to another system.
The broader point was basically that the Rails UI integration tests took a very long time, and required the whole system up, and we had a pretty large team constantly pushing changes. While not 100% unique to Rails, it was exacerbated by RoR conventions.
We moved much of the UI to a few Next.js apps where the tests were extremely fast and easy to run locally.
