The AWS SDKs and Command Line Interface (CLI) use a specific order of precedence to find credentials, known as the credential provider chain. By default, the shared credentials file (~/.aws/credentials) is checked before the IAM role attached to the EC2 instance. In this scenario, the application will find and use the IAM user's access keys from the credentials file. Since these keys grant full administrative access, the EC2 instance will be able to perform all S3 actions. The IAM role and its explicit deny policy are never evaluated because credentials were found earlier in the provider chain.

A. The EC2 instance will only be able to list the S3 buckets.

This is incorrect because the credentials being used provide full administrative access, not just the permission to list buckets.

B. The EC2 instance will only be able to list the contents of one S3 bucket at a time.

This is incorrect. The credentials used grant full administrative permissions, which are far more extensive than just listing bucket contents.

D. The EC2 instance will not be able to perform any S3 action on any S3 bucket.

This is incorrect because the IAM role with the explicit deny policy is not used. The credential provider chain selects the user credentials from the file first.

1. AWS SDK and Tools Reference Guide

"Configuration and credential settings": This document outlines the order of precedence for credentials. It states

"When you configure your credentials

you can use any of the methods described in this topic. The SDK or tool works through them in a specific order of precedence... 3. Shared credentials file (~/.aws/credentials and ~/.aws/config)... 5. IAM role for Amazon EC2". This confirms the credentials file is checked before the instance role.

2. AWS Identity and Access Management User Guide

"IAM roles for Amazon EC2": This guide explains how applications on an EC2 instance can use the credentials from an attached IAM role. However

it operates as part of the broader credential provider chain

which prioritizes other sources like the credentials file.

3. AWS Command Line Interface User Guide

Version 2

"Configuration and credential file settings": Under the section "Order of precedence for AWS CLI options and settings

" the documentation confirms the credential provider chain order

placing the shared credential file (awsaccesskeyid

awssecretaccesskey) before instance profile credentials.