Rails really does not scale. In performance or development. It’s still a great option for small sites though.

Done Rails my entire career. It scales more than you think if you’re willing to throw some hardware at it and avoid turning your controllers and models into logic layer soup.

What kills scaling is inexperienced developers doing what I just mentioned. Also, ActiveRecord is not your friend at scale. It’s wonderful in small amounts, but callbacks and memory overhead will kill you. You really need to learn SQL to avoid doing select * on seven tables.

Also, view partials. The lookup cost on those is pretty high.

To be fair, any framework scales if you throw hardware at it and stop using the slow bits.

The question is if there is anything meaningful left after you stoped using the slow bits.

Off the top of my head, I think Github and Gitlab are both based on Rails, as well as Shopify and Airbnb. So there are for sure some very large companies that use Rails successfully at scale. I can't speak to how difficult it was to develop or deploy, and it seems like Ruby as a whole has lost some popularity, but Rails has worked and continues to work for a lot of organizations.

It seems like a herculean effort to make it work from what I have seen at GitLab. Which includes having the majority of the site not in rails but Go microservices.

Personally I find that Ruby is more the problem than Rails. Having an untyped language makes things extremely difficult to work with as the app grows. Gem updates are very difficult to do safely.

GitHub is moving away from Rails to Go now. So have Twitch, Twitter, Stripe, LinkedIn, etc.