Introduction
IAM Policies in AWS are essential for managing and controlling access to resources. They define who can do what with which resources. In simple terms, policies are like the rules and guidelines that dictate access permissions, ensuring the right people (or services) have the right level of access.
- What Are IAM Policies?
IAM Policies are JSON documents that specify permissions for users, groups, and roles. They act as “permission slips” for accessing AWS resources, determining who can perform specific actions on which resources.
Analogy: Imagine policies as specific office access cards. Each access card defines which rooms a person can enter, whether they can only look around (read-only) or move things (full access). Just as access cards specify room permissions, IAM policies define permissions for AWS resources.
- Types of IAM Policies
AWS IAM offers several types of policies to meet different needs. Here’s a breakdown:
- Identity-Based Policies
These policies are attached to IAM users, groups, or roles and define what actions they can take. Think of them as “job roles” for employees, where each role specifies tasks, they’re authorized to perform. - Resource-Based Policies
Unlike identity-based policies, resource-based policies are attached directly to AWS resources, such as S3 buckets. These policies allow specific identities to access the resource, almost like putting a “restricted access” sign on a room that only certain people can enter. - Permissions Boundaries
Permissions boundaries set the maximum permissions an identity-based policy can grant. It’s similar to a ceiling limit on spending within a department; no matter what, permissions can’t exceed that boundary. - Service Control Policies (SCPs)
SCPs manage permissions across multiple AWS accounts within an organization. Imagine these as corporate-level guidelines that restrict what all departments (AWS accounts) can or can’t do.
- Structure of an IAM Policy
Each IAM Policy contains specific elements that define permissions. Here’s a quick look at the key elements:
- Effect: Specifies if the action is allowed (Allow) or denied (Deny).
- Action: Lists the actions the policy permits or restricts.
- Resource: Specifies the AWS resource the policy applies to.
- Condition: Defines conditions under which the policy is in effect.
Analogy: Picture each policy as a security rule card. If the card reads “Allow access to Room A,” only authorized employees can enter Room A. If the card says, “Deny access to Room B,” those employees are restricted from Room B, even if their job role usually grants them access. Conditions add extra rules—like “Only on weekdays”—to further refine access.
- Policy Evaluation Logic
When IAM evaluates a policy, it uses a specific process to determine whether to allow or deny an action. Here’s the order of operations:
- Explicit Deny: If a policy explicitly denies access, the action is denied.
- Explicit Allow: If a policy explicitly allows an action, it proceeds to check other policies.
- Implicit Deny: If there’s no explicit allow, the action is denied by default.
IAM Policy Evaluation
Diagram Reference-
https://tutorialsdojo.com/how-aws-iam-handles-conflicting-iam-policies/
Conclusion
IAM Policies are critical tools for ensuring secure, controlled access in AWS. By understanding and applying these policies effectively, you can build a robust security structure that keeps resources safe while enabling necessary access.