AWS DVA-C02 Drill: Lambda Permissions - Troubleshooting IAM Role Errors

Jeff’s Note

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

For AWS DVA-C02 candidates, confusion often arises around Lambda’s execution role permissions—specifically the difference between what the AWSLambdaBasicExecutionRole grants and what it doesn’t. In production, mastering granular IAM permissions to allow Lambda to call other AWS services without over-provisioning is crucial. Let’s drill down.

The Certification Drill (Simulated Question)

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Scenario

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CloudStream Solutions is developing a scheduled AWS Lambda function to monitor their AWS environment. The Lambda function is responsible for listing all Amazon S3 buckets in the account and saving those bucket names into a DynamoDB table for audit purposes. The developer assigned the AWSLambdaBasicExecutionRole managed policy to the function but encounters a permissions error when the Lambda executes.

The Requirement:

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Determine which combination of permissions must be added to the Lambda execution role to enable the function to list buckets in S3 and write records into DynamoDB successfully.

The Options

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• A) An IAM role to allow cross-account access from Lambda
• B) Permission for the Lambda function to list buckets in Amazon S3
• C) Permission for the Lambda function to write items to the DynamoDB table
• D) Permission for Amazon S3 to invoke the Lambda function
• E) Permission for DynamoDB to invoke the Lambda function

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leave a comment:

Correct Answer

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B) Permission for the Lambda function to list buckets in Amazon S3
C) Permission for the Lambda function to write items to the DynamoDB table

Quick Insight: The AWS DVA-C02 Imperative

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In Lambda permission errors, the AWSLambdaBasicExecutionRole policy only grants basic CloudWatch Logs writing permissions, not access to other AWS services.
You must explicitly attach permissions for the Lambda function to call S3’s ListBuckets and DynamoDB’s PutItem API actions.

Content Locked: The Expert Analysis

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

The Expert’s Analysis

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Correct Answer

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Options B and C

The Winning Logic

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The AWS managed policy AWSLambdaBasicExecutionRole provides only minimal permissions needed for Lambda execution environment, such as logging to CloudWatch Logs. It does not include any permissions for accessing S3 or DynamoDB. To allow the Lambda function to:

• List S3 buckets, the execution role requires the s3:ListAllMyBuckets or s3:ListBucket permissions on the S3 service. This enables API calls like ListBuckets() to succeed.
• Write entries into DynamoDB, the execution role must have dynamodb:PutItem or dynamodb:UpdateItem permissions on the target DynamoDB table to persist the bucket list.

By attaching a custom inline policy or managed policy granting these permissions to the same execution role, the function will have the access it needs.

The Trap (Distractor Analysis):

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• Why not A? A cross-account IAM role is irrelevant here since all operations occur within the same AWS account. This adds unnecessary complexity.
• Why not D or E? These options reflect service-to-Lambda invocation permissions (e.g., S3 event triggers or DynamoDB streams invoking Lambda). But the function is running on a schedule, not invoked by S3 or DynamoDB, so these permissions are unnecessary.

The Technical Blueprint

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B) For Developer (Code/CLI Snippet):

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Example of the minimal JSON IAM policy to attach to the Lambda execution role:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": "s3:ListAllMyBuckets",
      "Resource": "*"
    },
    {
      "Effect": "Allow",
      "Action": [
        "dynamodb:PutItem",
        "dynamodb:UpdateItem"
      ],
      "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/YourBucketAuditTable"
    }
  ]
}

Or add these permissions via AWS CLI to an existing role:

aws iam put-role-policy \
  --role-name YourLambdaExecutionRole \
  --policy-name S3DynamoAccessPolicy \
  --policy-document file://s3-dynamo-policy.json

The Comparative Analysis

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Real-World Application (Practitioner Insight)

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Exam Rule

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“For the exam, always remember that AWSLambdaBasicExecutionRole is not a catch-all permission role—you need to explicitly grant service access permissions.”

Real World

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“While you can add all permissions in one broad role, it’s best practice in real deployments to practice least privilege for security and auditability.”

(CTA) Stop Guessing, Start Mastering

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Disclaimer

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