Access Control Lists (ACLs)

• Description: ACLs are a legacy access control mechanism that was used before IAM policies.
• How it works: They allow you to manage access to buckets and objects. Each bucket and object has an ACL attached to it as a subresource.
• Benefits: They provide a quick way to grant cross-account access to your S3 resources.
• Limitations: They do not provide the same fine-grained control as IAM policies.
• Features: They allow read/write permissions at a high level.
• Use Cases: They are typically used when you need to manage permissions for individual objects in a bucket.

Bucket Policies

• Description: Bucket policies are IAM policies that are attached directly to a bucket.
• How it works: They allow you to grant other AWS accounts or IAM users access to the bucket and the objects in it.
• Benefits: They provide more fine-grained control than ACLs.
• Limitations: They only apply to the bucket they are attached to.
• Features: They allow permissions to be set for multiple objects within a single bucket.
• Use Cases: They are typically used when you want to grant permissions to multiple objects within a bucket without managing permissions for each object individually.

IAM Policies

• Description: IAM policies define permissions for an IAM user, group, or role.
• How it works: They allow you to specify who has access to what resources in your AWS environment.
• Benefits: They provide the most granular control over access to resources.
• Limitations: They require more management than ACLs or bucket policies.
• Features: They allow permissions to be set for any AWS service, not just S3.