This solution correctly addresses both secure connectivity and granular access control with minimal operational overhead. A gateway VPC endpoint for Amazon S3 allows EC2 instances to access S3 using private IP addresses, keeping traffic within the AWS network and avoiding the public internet. This is more secure and cost-effective than using a NAT gateway.

An IAM instance profile attached to the EC2 instances is the standard method for granting permissions. The associated IAM policy can be configured to grant access only to specific S3 buckets, enforcing the principle of least privilege. By using wildcards in the bucket ARN (e.g., arn:aws:s3:::company-customer-), the policy can automatically apply to new customer buckets without modification, thus ensuring low operational overhead.

B: A NAT gateway routes traffic over the public internet to reach S3, which is less secure than a VPC endpoint. It also fails to specify how access control to specific buckets would be enforced.

C: While a gateway endpoint is correct, this option describes an incomplete policy. A Deny policy acts as a guardrail but does not grant permissions. An explicit Allow action is still required for the instances to access any buckets.

D: Using a NAT gateway is inefficient for this use case. Furthermore, managing individual bucket policies for every customer bucket creates significant operational overhead compared to managing a single IAM role policy.

1. AWS Documentation - VPC Endpoints for Amazon S3: "A gateway endpoint is a gateway that you specify as a target for a route in your route table for traffic destined to a supported AWS service... Gateway endpoints are supported for Amazon S3 and DynamoDB." This confirms the use of a gateway endpoint for private S3 access. (Source: AWS VPC User Guide

"Gateway VPC endpoints").

2. AWS Documentation - IAM Roles for Amazon EC2: "Applications must sign their API requests with AWS credentials. Therefore

if you are an application developer

you need a strategy for managing credentials for your applications that run on EC2 instances... We recommend that you use IAM roles for Amazon EC2." (Source: AWS IAM User Guide

"IAM roles for Amazon EC2").

3. AWS Documentation - Policies and Permissions in Amazon S3: "You can use wildcards () as part of the resource ARN... For example

you can use the following Resource element to grant permission to objects in a specific bucket where the object keys are prefixed with logs/." This supports using wildcards in an IAM policy for low-overhead management. (Source: Amazon S3 User Guide

"Policies and permissions in Amazon S3"

section on "Specifying resources in a policy").

4. AWS Documentation - aws:ResourceAccount Condition Key: "Use this key to compare the AWS account ID of the resource in the request with the account ID that you specify in the policy." While this key is valid for creating account-level guardrails

option C's reliance solely on a Deny policy makes it an incomplete solution for granting access. (Source: AWS IAM User Guide

"AWS global condition context keys").