A company has an application that is hosted on Amazon EC2 instances. The application stores objects in an Amazon S3 bucket and allows users to download objects from the S3 bucket. A developer turns…

An EC2 instance profile attaches an IAM role to the EC2 fleet, allowing the application to assume AWS credentials via the instance metadata service. This eliminates hardcoded access keys and is the secure, recommended way to grant EC2 applications access to S3.

Storing an IAM user's long-lived access key ID and secret access key on the EC2 instance is a security anti-pattern; these credentials can be exposed in the event of an instance compromise and are harder to rotate than instance profile roles.

The S3 GeneratePresignedUrl API call uses the application's IAM credentials (from the instance profile) to sign a time-limited URL for a specific object. The application only generates and returns a presigned URL to authenticated users, ensuring that S3 itself remains private while authorized access is granted securely without exposing credentials to the client.

Having the application fetch the S3 object and return it directly to the user routes all object data through the EC2 instance, increasing bandwidth costs, adding latency, and creating a bottleneck compared to presigned URLs which allow direct client-to-S3 transfers.

Delegating requests directly to the S3 bucket without presigned URL signing or IAM-based access control does not define a secure, authenticated access mechanism and is too vague to constitute a complete solution.