1The Universal API
Underneath the hood, the AWS Management Console, the AWS CLI, and all the SDKs perform the exact same action: they make REST API calls to AWS endpoints. Understanding the CLI gives you a deeper understanding of these underlying APIs.
2The Credential Hierarchy
When you run an SDK application, it searches for credentials. First, it checks environment variables (AWS_ACCESS_KEY_ID). If not found, it checks ~/.aws/credentials. If not found, it checks if it's running on an EC2 instance or Lambda with an attached IAM Role. Relying on IAM Roles in production is the most secure method.
