What should a security engineer do to troubleshoot this issue?
Confirm that the Elastic Beanstalk service role has access to Amazon S3.
Confirm that the Elastic Beanstalk instance profile has access to Amazon S3.
Confirm that the AWSElasticBeanstalkFullAccess managed policy is attached to the Elastic Beanstalk environment.
Confirm that the S3 bucket policy allows access from the Elastic Beanstalk application ARN.
Explanations:
The Elastic Beanstalk service role is used by the Elastic Beanstalk management service, not by the EC2 instances running the application. The EC2 instances need the appropriate permissions, not the service role.
The Elastic Beanstalk instance profile is an IAM role that is associated with the EC2 instances running the application. This role needs the appropriate permissions to access Amazon S3.
The AWSElasticBeanstalkFullAccess managed policy grants full access to Elastic Beanstalk resources, but it does not grant permissions to S3. The necessary permissions to S3 need to be granted explicitly to the instance profile.
The S3 bucket policy controls access to the bucket but would not typically grant access to Elastic Beanstalk instances. The IAM role associated with the instance profile should grant the permissions to access S3.