Which method can be used to prevent an IP address block from accessing public objects in an S3 bucket?
Create a bucket policy and apply it to the bucket
Create a NACL and attach it to the VPC of the bucket
Create an ACL and apply it to all objects in the bucket
Modify the IAM policies of any users that would access the bucket
Explanations:
A bucket policy can be used to explicitly deny access to certain IP address blocks, preventing those IPs from accessing the public objects in the S3 bucket.
Network Access Control Lists (NACLs) apply to VPC subnets and control inbound/outbound traffic at the network level. S3 bucket policies are independent of VPC NACLs and cannot be controlled via them.
Access Control Lists (ACLs) control permissions for individual objects and buckets but do not provide a method to block access based on IP address. Bucket policies are a better fit for this use case.
Modifying IAM policies can restrict access to the bucket for specific users or roles but does not block access based on IP addresses. IP restrictions are more effectively handled in bucket policies.
From my point of view, the answer is:
Create a bucket policy and apply it to the bucket