See this SO post
it is still possible to host your sitemap on external S3 buckets. You must set up a subdomain of your domain pointed as an Alternative Domain Name for your CloudFront distribution, and in order to do this you must go through domain verification with AWS.
Tested codebases are the most signficiant development from Rails and Agile over the last 15 years. End-to-end testing, in particular, is the defining reason why Agile and Rails have been so successful. Not writing tests should be seen as akin to malpractice in software development. Hiring someone to write untested code should be outlawed.
Confusingly, bundler can have more than one version of Rails installed at once. In this short post, I will review how to check which version of Rails bundler has installed, and how to know which version of Rails you are using to make a new Rails app.