Rails 5.1 introduced encrypted secrets, which gives you two places to put your secrets -- secrets. yml and secrets.yml.enc. This causes a bit of confusion on when you should use normal secrets or encrypted secrets.
Credentials is a new feature on Rails 5.2 which replaces secrets and encrypted secrets. Under the hood Credentials use EncryptedConfiguration which you can reuse if you need to use encryption on other parts of your application.
This blog post is a step by step tutorial on how to set up PostgreSQL Replication between AWS regions. This is an essential part of our disaster recovery plan at Engine Yard. A previous blog post gives a higher level overview on disaster recovery.