ACL vs Bucket Policy in S3: Key Differences and Usage Guide

In AWS S3, ACL (Access Control List) controls access at the individual object or bucket level with simple permissions, while bucket policy is a JSON-based policy that offers fine-grained, flexible access control for the entire bucket or objects. Bucket policies are more powerful and recommended for most access management tasks over ACLs.

Quick Comparison

Here is a quick side-by-side comparison of ACL and bucket policy in S3.

Factor	ACL	Bucket Policy
Control Level	Object or bucket level	Bucket or objects within bucket
Format	Simple grantee and permission list	JSON policy with conditions
Flexibility	Limited permissions (read, write, full control)	Fine-grained with conditions and multiple actions
Use Case	Basic access control, legacy support	Complex access rules, cross-account access
Management	Harder to audit and manage at scale	Easier to manage and audit centrally
Recommended	Not recommended for new setups	Recommended for most access control needs

Key Differences

ACL is an older, simpler way to grant access to buckets or objects by listing grantees and their permissions directly. It supports basic permissions like READ, WRITE, and FULL_CONTROL but lacks the ability to specify conditions or complex rules.

In contrast, bucket policy uses JSON documents to define detailed access rules. It supports multiple actions, conditions (like IP address restrictions), and can grant access to multiple AWS accounts or IAM users. Bucket policies apply at the bucket level but can control access to specific objects using prefixes.

Because bucket policies are more flexible and easier to audit, AWS recommends using them over ACLs for most access control scenarios. ACLs remain for backward compatibility and simple use cases.

ACL Code Example

This example shows how to set a bucket ACL to grant read access to everyone.

xml

<AccessControlPolicy>
  <Owner>
    <ID>owner-id</ID>
  </Owner>
  <AccessControlList>
    <Grant>
      <Grantee xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="Group">
        <URI>http://acs.amazonaws.com/groups/global/AllUsers</URI>
      </Grantee>
      <Permission>READ</Permission>
    </Grant>
  </AccessControlList>
</AccessControlPolicy>

Output

Bucket ACL updated to allow public read access

Bucket Policy Equivalent

This JSON bucket policy grants read access to everyone for all objects in the bucket.

json

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

Output

Bucket policy applied to allow public read access to all objects

When to Use Which

Choose ACL only for simple, legacy scenarios where you need to quickly grant basic permissions on individual objects or buckets. Avoid ACLs for new projects because they are limited and harder to manage.

Choose bucket policy when you need flexible, fine-grained access control with conditions, cross-account permissions, or centralized management. Bucket policies are the modern, recommended approach for controlling access to S3 buckets and objects.

Key Takeaways

Bucket policies offer more flexible and fine-grained access control than ACLs.

ACLs are simpler but limited and mainly for legacy support.

Use bucket policies for most new S3 access control needs.

Bucket policies support JSON conditions and multiple actions.

ACLs control access at object or bucket level with basic permissions.