Which solution meets these requirements with the LEAST amount of operational overhead?
Add the aws:PrincipalOrgID global condition key with a reference to the organization ID to the S3 bucket policy.
Create an organizational unit (OU) for each department. Add the aws:PrincipalOrgPaths global condition key to the S3 bucket policy.
Use AWS CloudTrail to monitor the CreateAccount, InviteAccountToOrganization, LeaveOrganization, and RemoveAccountFromOrganization events. Update the S3 bucket policy accordingly.
Tag each user that needs access to the S3 bucket. Add the aws:PrincipalTag global condition key to the S3 bucket policy.
Explanations:
Adding theaws:PrincipalOrgIDglobal condition key to the S3 bucket policy allows access only to users from accounts within the same AWS Organization. This approach is straightforward and requires minimal operational overhead since it directly restricts access based on the organization ID without additional complexity.
While using theaws:PrincipalOrgPathscondition key can provide more granular control based on organizational units (OUs), it adds unnecessary complexity and management overhead, especially if the organization structure is not stable or changes frequently. It is not the most efficient way to meet the requirement.
Using AWS CloudTrail to monitor account changes and updating the S3 bucket policy accordingly introduces significant operational overhead. This solution requires continuous monitoring and manual updates to the policy whenever there are changes in the accounts, which is not ideal for minimizing operational efforts.
Tagging users with theaws:PrincipalTagglobal condition key adds a layer of complexity since it requires managing user tags effectively. This approach also does not inherently limit access to only users from the organization, as users from outside the organization could still be tagged similarly.
I weigh that the answer is:
Add the aws:PrincipalOrgID global condition key with a reference to the organization ID to the S3 bucket policy.