Here are the headline changes:
- Active Storage - includes providers like S3 and its ilk, creating variants, and async metadata extraction
- Redis Cache Store - supports distributed Redis for sharding with changes that can drastically improve cache lifetime
- HTTP/2 Early Hints - faster loading for related assets like JS/CSS
- CSP - a new Content Security Policy DSL (Domain Specific Language) to configure Rails apps
- Credentials - Encrypted credentials for your app, like AWS access keys and other secrets. They can be checked into revision control without needing to maintain a large number of environment variables.
- bootsnap - This gem is now included by default and reduces application boot times by over 50%.