IAM (Identity and Access Management) controls who can do what in AWS — managing users, groups, roles, and permissions. It's fundamental to AWS security: every action is authorized through IAM, so understanding it is essential.
What IAM manages
IAM controls AUTHENTICATION (who you are) and AUTHORIZATION (what you can do):
USERS → individual identities (people or applications) with credentials
GROUPS → collections of users (assign permissions to a group → all its users get them)
ROLES → identities ASSUMED temporarily (by users, services, or AWS resources)
— no permanent credentials; key for services/cross-account access
POLICIES → JSON documents defining PERMISSIONS (what actions on what resources)
