Which solution will meet these requirements in the MOST secure manner?
Apply an S3 bucket policy that grants read access to the S3 bucket.
Apply an IAM role to the Lambda function. Apply an IAM policy to the role to grant read access to the S3 bucket.
Embed an access key and a secret key in the Lambda function’s code to grant the required IAM permissions for read access to the S3 bucket.
Apply an IAM role to the Lambda function. Apply an IAM policy to the role to grant read access to all S3 buckets in the account.
Explanations:
While applying an S3 bucket policy could grant read access, it is generally more secure and manageable to use IAM roles and policies specifically associated with the Lambda function. Bucket policies can potentially expose the bucket to unintended access if not carefully managed.
Applying an IAM role to the Lambda function and an IAM policy to grant read access to the specific S3 bucket is the most secure method. This approach adheres to the principle of least privilege and allows for easy management of permissions, as roles can be updated without changing the function code.
Embedding an access key and secret key in the Lambda function’s code is insecure. It risks exposing the keys if the code is ever shared or if the function is misconfigured. AWS best practices recommend using IAM roles instead of hardcoding credentials.
While this option grants read access to the S3 bucket, it is too broad as it allows read access to all S3 buckets in the account. This violates the principle of least privilege, which advocates granting the minimum necessary permissions to perform a task.
I suspect that the answer is:
Apply an IAM role to the Lambda function. Apply an IAM policy to the role to grant read access to the S3 bucket.