超越基础 IAM,理解 roles(假定的身份)、policy types 和 evaluation(权限如何确定)以及 cross-account access 和 service roles 等模式对于安全、架构良好的 AWS 访问管理很重要。
深入了解 Roles — 谁假定什么
A ROLE has TWO key policies:
TRUST POLICY → WHO can assume the role (which principals: a service, account, user)
PERMISSION POLICIES → WHAT the role can do once assumed
Use cases:
→ SERVICE roles — an EC2/Lambda assumes a role to access AWS (no embedded keys)
→ CROSS-ACCOUNT — account B's role trusts account A → A's users assume it (controlled access)
→ FEDERATION/SSO — external identities assume roles (temporary credentials)
→ Roles give TEMPORARY credentials (auto-rotated) — far safer than long-lived keys.
