AWS DVA-C02 Drill: IAM Roles and Policies - Understanding EC2 Instance Permissions

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, the confusion often lies in which IAM policy actually governs permissions for EC2 instances when accessing AWS services. In production, this is about knowing exactly how the EC2 instance profile role authorizes API calls from your application code. Let’s drill down.

The Certification Drill (Simulated Question)

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Scenario

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A software company, DataStream Innovations, develops a cloud application deployed on a fleet of Amazon EC2 instances. The application is being extended with a feature to upload processed data files to an Amazon S3 bucket for archival. As the lead developer, you need to ensure your EC2 instances have the proper permissions to write these files directly to S3.

The Requirement:

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Identify which policy must be modified or attached to allow the EC2 instances to successfully write objects to the S3 bucket without additional manual authentication.

The Options

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• A) The IAM policy that is attached to the EC2 instance profile role
• B) The session policy that is applied to the EC2 instance role session
• C) The AWS Key Management Service (AWS KMS) key policy that is attached to the EC2 instance profile role
• D) The Amazon VPC endpoint policy

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Correct Answer

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A

Quick Insight: The Developer Imperative

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When EC2 instances need AWS service access, the IAM role attached as the instance profile defines their permissions scope. Session policies are temporary and less common; KMS key policies govern encryption but not basic S3 write access; and VPC endpoint policies only control traffic routing, not IAM permissions.

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 from a Senior?

The Expert’s Analysis

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Correct Answer

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Option A

The Winning Logic

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For applications running on EC2 instances, AWS uses IAM roles attached to these instances via the instance profile mechanism to provide the AWS credentials automatically through the instance metadata service (IMDS). The EC2 instance profile role’s IAM policy must grant PutObject or similar permissions to the target S3 bucket. This allows the application running inside the EC2 instance to upload objects securely without embedding static credentials.

• Session policies (Option B): These are optional additional policies that further restrict permissions during a temporary role session, but are not typically used or modified for this kind of basic EC2 role setup.
• KMS key policies (Option C): Relevant only if the S3 bucket objects are encrypted with customer-managed keys and you want to allow the EC2 role to use the encryption keys. However, granting write access to S3 objects normally requires proper IAM permissions on the bucket first.
• VPC endpoint policies (Option D): These restrict access when accessing S3 through a VPC endpoint, but do not grant or modify who can write to S3—permissions are governed by IAM roles and bucket policies.

The Trap (Distractor Analysis):

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• Why not B? Session policies are advanced control mechanisms, rarely required just to enable EC2 instance S3 writes.
• Why not C? KMS policies control decryption/encryption permissions, not basic bucket write permissions.
• Why not D? VPC endpoint policies are about network-level access and do not grant IAM permissions to write objects.

The Technical Blueprint

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# Example minimal IAM policy attached to the EC2 instance profile role to allow writing to S3
aws iam put-role-policy --role-name EC2DataUploaderRole --policy-name S3WritePolicy --policy-document '{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": ["s3:PutObject"],
      "Resource": ["arn:aws:s3:::datastream-archive-bucket/*"]
    }
  ]
}'

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 pick IAM policy attached to EC2 instance profile role when asked about EC2 permissions for AWS service access.

Real World

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While sometimes a bucket policy or KMS policy adjustment is necessary, the IAM role attached to EC2 is almost always the first place to grant direct write access to S3 from EC2 applications.

(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.