AWS DVA-C02 Drill: Secure Lambda S3 Access - Temporary Credentials Best Practice

Jeff’s Note

#

Unlike generic exam dumps, ADH analyzes this scenario through the lens of a Real-World Lead Developer.

For DVA-C02 candidates, the confusion often lies in how best to securely grant Lambda access to S3 with minimal credential exposure. In production, this is about knowing exactly when to use IAM execution roles versus embedding or retrieving credentials dynamically. Let’s drill down.

The Certification Drill (Simulated Question)

#

Scenario

#

TechNova Inc. has developed a serverless analytics application running on AWS Lambda. The application needs to retrieve highly sensitive configuration files stored in a specific S3 bucket. The software engineering principle in use mandates granting only the minimum necessary permissions, and the company wants to avoid any long-lived static credentials embedded in the function code or environment.

The Requirement:

#

As the lead developer, you must ensure the Lambda function can securely access specific objects in the S3 bucket using temporary credentials, minimizing attack surface and adhering to least privilege.

The Options

#

• A) Hardcode AWS access keys with permissions to the S3 bucket directly into the Lambda function code and use those keys for S3 access.
• B) Generate an AWS access key ID and secret access key with S3 permissions and store them in AWS Secrets Manager. Have the Lambda function retrieve these secrets at runtime and use them to access the S3 objects.
• C) Create an IAM role specifically for the Lambda function execution. Attach an IAM policy to this role that grants access only to the necessary S3 objects. Assign this role to the Lambda function.
• D) Generate an AWS access key ID and secret access key with S3 permissions and set them as environment variables in the Lambda function configuration. Use these environment variables in the function code to access the S3 objects.

Google adsense

#

leave a comment:

Correct Answer

#

C

Quick Insight: The Developer’s Imperative

#

The key is trusting Lambda execution roles to provide temporary, automatically rotated credentials scoped with fine-grained permissions — eliminating static keys that risk exposure.
Options A, B, and D all involve managing long-lived credentials manually, violating AWS best practices and increasing risk.

Content Locked: The Expert Analysis

#

You’ve identified the answer. But do you know the implementation details that separate a Junior from a Senior?

The Expert’s Analysis

#

Correct Answer

#

Option C

The Winning Logic

#

Assigning an IAM execution role with a tailored IAM policy to your Lambda function is the most secure, scalable, and maintainable practice. AWS automatically provides temporary credentials to the Lambda runtime via the role. The credentials rotate transparently, minimizing risk of compromise.

• Lambda assumes the role at invocation time.
• The policy should use resource-level permissions restricting access to only the specific S3 bucket and objects.
• No hardcoded or static credentials are stored in code or environment variables.
• This fits well with CI/CD workflows and automated deployments.

The Trap (Distractor Analysis):

#

• Why not A?
  Hardcoding credentials in code risks accidental exposure in source repositories and is a major security anti-pattern.

• Why not B?
  While fetching credentials from Secrets Manager avoids hardcoding, it still relies on long-lived static IAM user keys, which contradicts the principle of temporary credentials and increases credential management complexity.

• Why not D?
  Storing static credentials in environment variables is similarly insecure because if an attacker gains access to Lambda environment config, credentials can be leaked. Plus, the credentials do not rotate automatically.

The Technical Blueprint

#

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": ["s3:GetObject"],
      "Resource": ["arn:aws:s3:::confidential-config-bucket/path/to/secret/*"]
    }
  ]
}

# Attach the policy to the Lambda execution role (example CLI)
aws iam put-role-policy --role-name LambdaExecutionRole --policy-name AccessS3SecretsPolicy --policy-document file://policy.json

The Comparative Analysis

#

Real-World Application (Practitioner Insight)

#

Exam Rule

#

For the exam, always pick IAM execution roles when you see Lambda needing AWS resource access.

Real World

#

In production, embedding credentials—even in Secrets Manager—adds operational overhead and risk. Using roles leverages native AWS identity features for secure, auditable, and ephemeral access.

(CTA) Stop Guessing, Start Mastering

#

Disclaimer

This is a study note based on simulated scenarios for the AWS DVA-C02 exam.