I recently upgraded an old website[1] stuck on Rails 4.2 / Ruby 2.4 (yeah, I know) to Rails 8.1 / Ruby 4.0 and it's still awesome as it was in the first days of Rails 2.3 back in the days. Such a great framework and language to work with!
railsdiff.org was really helpful to upgrade in addition to the official documentation, especially now with LLMs that can process all these text and assist you in the process.
It has become easier and easier to upgrade Rails over time. 2 of my apps were running 2 versions back and the most difficult thing was finding the time to update it. There was one gem that was deprecated but the replacement was 10 lines of code. Overall I'd say that Rails is such a robust choice nowadays.
My favorite part of Rails 8 is the focus on reducing infrastructure and just defaulting to the DB for queue (SolidQueue) / caching (SolidCache), such a nice out of the box experience.
railsdiff.org was really helpful to upgrade in addition to the official documentation, especially now with LLMs that can process all these text and assist you in the process.
[1]: https://news.ycombinator.com/item?id=49587692