AWS DVA-C02 Drill: Lambda IAM Permissions - Secure Access with Roles vs. Keys

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 to securely grant AWS Lambda the minimal permissions it needs without exposing static credentials inside code or environment variables.

In production, this is about knowing exactly when to use IAM roles versus embedding IAM user keys, and understanding Lambda’s native integration with IAM roles for secure delegation. Let’s drill down.

The Certification Drill (Simulated Question)

#

Scenario

#

Acme Analytics is building a serverless data processing pipeline. A Lambda function processes event data and needs to read files from an Amazon S3 bucket and also read/write items in a DynamoDB table. The correct IAM policy granting these permissions already exists.

The Requirement:

#

What is the MOST secure method to grant the Lambda function access to read from the S3 bucket and read/write to the DynamoDB table?

The Options

#

• A) Attach the existing IAM policy directly to the Lambda function.
• B) Create an IAM role for the Lambda function, attach the existing IAM policy to the role, then assign the role to the Lambda function.
• C) Create an IAM user with programmatic access, attach the existing policy to the user, and add the user’s access key ID and secret access key as environment variables in the Lambda function.
• D) Add the AWS root account access key ID and secret access key as encrypted environment variables in the Lambda function.

Google adsense

#

leave a comment:

Correct Answer

#

B

Quick Insight: The Developer Security Imperative

#

Lambda natively supports IAM roles that securely provide permissions without embedding static credentials, enforcing the principle of least privilege and mitigating risk of accidental credential exposure.

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 B

The Winning Logic

#

Attaching an IAM role with the existing policy to the Lambda function leverages Lambda’s built-in ability to assume roles securely at runtime. This avoids embedding static credentials, reduces management overhead, and follows AWS best practices for short-lived, automatically rotated permissions.

• Lambda execution environments automatically retrieve and use temporary credentials from the associated IAM role.
• This enables granular least-privilege assignment using the existing IAM policy.
• No sensitive access keys are exposed in environment variables or code, reducing security risks.

The Trap (Distractor Analysis):

#

• Why not A? IAM policies cannot be attached directly to a Lambda function itself; policies attach to IAM identities such as users or roles. This is a misunderstanding of AWS IAM architecture.
• Why not C? Supplying IAM user access keys statically in Lambda environment variables is a bad security practice. Access keys could be leaked accidentally, they never rotate automatically, and keys tied to a long-lived user break the least privilege model.
• Why not D? Embedding root account keys in any environment—encrypted or not—is extremely dangerous. Root credentials grant full account control, violating security principles and AWS best practices. Root keys should never be used this way.

The Technical Blueprint

#

Code Snippet: Assigning IAM Role to Lambda (AWS CLI)

#

# Create an IAM role trust policy for Lambda
cat > trust-policy.json << EOF
{
  "Version": "2012-10-17",
  "Statement": [{
    "Effect": "Allow",
    "Principal": {"Service": "lambda.amazonaws.com"},
    "Action": "sts:AssumeRole"
  }]
}
EOF

# Create the role
aws iam create-role --role-name AcmeLambdaExecutionRole --assume-role-policy-document file://trust-policy.json

# Attach the existing IAM policy to the role
aws iam attach-role-policy --role-name AcmeLambdaExecutionRole --policy-arn arn:aws:iam::123456789012:policy/AcmeLambdaS3DynamoPolicy

# Update the Lambda function to use the role
aws lambda update-function-configuration --function-name AcmeDataProcessor --role arn:aws:iam::123456789012:role/AcmeLambdaExecutionRole

The Comparative Analysis

#

Real-World Application (Practitioner Insight)

#

Exam Rule

#

For the exam, always pick IAM Role when you see Lambda function needing AWS service access without manual management of credentials.

Real World

#

In reality, teams sometimes revert to using IAM user keys in environment variables for quick development or legacy reasons—but this creates serious security liabilities, trouble rotating credentials, and cannot scale. The managed role approach is the industry standard for serverless security.

(CTA) Stop Guessing, Start Mastering

#

Disclaimer

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