IAM Resource-Based Policies vs. IAM Roles for Cross-Account Access on AWS

When designing secure, cross-account architectures on AWS, a common consideration is whether to use IAM resource-based policies or IAM roles to grant permissions. Each approach offers specific advantages, and understanding when to use each can simplify management and improve security. This article covers the differences between IAM resource-based policies and IAM roles, common use cases, and best practices for leveraging them effectively in cross-account scenarios.

Understanding IAM Resource-Based Policies vs. IAM Roles

IAM Resource-Based Policies

IAM resource-based policies are policies attached directly to AWS resources. These policies specify which principals (users, roles, services) can access the resource and what actions they are allowed to perform. Resource-based policies are commonly used for resources like:

• Amazon S3 buckets
• Amazon SNS topics
• Amazon SQS queues
• AWS Lambda functions
• Amazon API Gateway

Key Characteristics of Resource-Based Policies

• No Need to Assume a Role: With resource-based policies, principals retain their permissions and do not need to assume another role to access the resource. This can be advantageous if you want the user or application to retain…