AWS IAM Inline vs. Managed Policies

Amazon Web Services (AWS) Identity and Access Management (IAM) is a web service that helps you securely control access to AWS resources. IAM policies are the foundation of access control in AWS, defining what actions are allowed or denied for specific users, groups, or roles. There are two primary types of IAM policies: inline policies and managed policies. Understanding the differences between these policy types is crucial for effective AWS security management.

What are IAM Policies?

IAM policies are JSON documents that define permissions in AWS. They specify:

• Effect: Whether the policy allows or denies access
• Action: The specific AWS service actions that are allowed or denied
• Resource: The AWS resources to which the actions apply
• Principal: The entity (user, group, or role) to which the policy applies
• Condition: Optional circumstances under which the policy applies

Policies are attached to IAM identities (users, groups, or roles) to grant or restrict access to AWS resources.

Inline Policies

Inline policies are policies that have a one-to-one relationship with an identity (user, group, or role). They are created and managed directly within the identity and cannot be reused across multiple identities.

Key Characteristics of Inline Policies:

• Direct Attachment: Inline policies are directly embedded within a single IAM identity
• One-to-One Relationship: Each inline policy belongs to exactly one identity
• No Standalone Existence: Inline policies don't exist independently; they are deleted when the associated identity is deleted
• Identity-Specific: Cannot be attached to multiple identities

When to Use Inline Policies:

• Unique Permissions: When you need to grant very specific permissions that are unique to a single identity
• Strict One-to-One Relationship: When you want to ensure that permissions are tightly coupled with a specific identity
• Custom Requirements: For highly customized access patterns that won't be reused

Example Inline Policy:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": "s3:GetObject",
      "Resource": "arn:aws:s3:::my-specific-bucket/*"
    }
  ]
}

Managed Policies

Managed policies are standalone identity-based policies that have their own Amazon Resource Name (ARN). They can be attached to multiple users, groups, or roles within your AWS account or across accounts.

Types of Managed Policies:

1. AWS Managed Policies: Created and maintained by AWS, covering common use cases
2. Customer Managed Policies: Created and maintained by you, providing custom permissions

Key Characteristics of Managed Policies:

• Reusable: Can be attached to multiple identities
• Standalone Existence: Exist independently of any specific identity
• Versioning: Support policy versioning for change management
• Central Management: Can be managed from a central location
• ARN Identification: Each managed policy has a unique ARN

When to Use Managed Policies:

• Common Permissions: When multiple identities need similar permissions
• Standardization: For enforcing consistent permissions across your organization
• Change Management: When you need versioning and rollback capabilities
• Reusability: For permissions that will be used across multiple identities

Example Customer Managed Policy:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "s3:ListBucket",
        "s3:GetObject",
        "s3:PutObject"
      ],
      "Resource": [
        "arn:aws:s3:::company-data-bucket",
        "arn:aws:s3:::company-data-bucket/*"
      ]
    }
  ]
}

Key Differences Between Inline and Managed Policies

Best Practices

Use Managed Policies When:

• Multiple identities need the same permissions
• You want to standardize permissions across your organization
• You need versioning and change management capabilities
• You want to simplify permission management

Use Inline Policies When:

• You need very specific, one-off permissions
• The permissions are tightly coupled with a single identity
• You want to ensure permissions are deleted with the identity
• You have unique requirements that don't warrant a managed policy

General Guidelines:

• Start with AWS Managed Policies: Use AWS-provided managed policies for common scenarios
• Create Customer Managed Policies: For standardized permissions specific to your organization
• Use Inline Policies Sparingly: Reserve for truly unique, identity-specific requirements
• Regular Reviews: Periodically review and audit both inline and managed policies
• Principle of Least Privilege: Grant only the minimum permissions necessary

Policy Limits and Considerations

• Policy Size: Inline policies are limited to 2,048 characters, while managed policies can be up to 6,144 characters
• Policy Count: Each identity can have up to 10 inline policies and 10 attached managed policies
• Versioning: Managed policies support up to 5 versions, allowing for easier rollback and change management
• Cross-Account Sharing: Managed policies can be shared across AWS accounts more easily than inline policies

Migration Strategies

If you're currently using primarily inline policies and want to move to managed policies:

1. Audit Existing Policies: Identify common permission patterns
2. Create Customer Managed Policies: Develop standardized managed policies for common use cases
3. Gradual Migration: Replace inline policies with managed policies incrementally
4. Testing: Thoroughly test new managed policies before full deployment
5. Documentation: Document the purpose and scope of each managed policy

Conclusion

Both inline and managed policies serve important roles in AWS IAM. Managed policies offer better scalability, reusability, and management capabilities, making them suitable for most use cases. Inline policies provide flexibility for unique, identity-specific requirements. The key is to understand when to use each type and follow AWS best practices for policy management. By leveraging the appropriate policy type for each scenario, you can maintain a secure, scalable, and manageable IAM infrastructure in your AWS environment.

Effective IAM policy management is crucial for maintaining security while enabling productivity. Whether you choose inline or managed policies, always follow the principle of least privilege and regularly review your policies to ensure they continue to meet your security requirements.