AWS DVA-C02 Drill: S3 VPC Endpoint Security - Precise Bucket Policy Enforcement

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 DVA-C02 candidates, the confusion often lies in how to utilize condition keys like aws:SourceVpce correctly in S3 bucket policies. In production, this is about knowing exactly how to tightly scope bucket access to multiple VPC endpoints without mistakenly allowing unintended networks. Let’s drill down.

The Certification Drill (Simulated Question)

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Scenario

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Streamline CloudApps, a fintech startup specializing in payment APIs, has a VPC that contains multiple gateway endpoints for Amazon S3. Their developers want to enforce security by ensuring that all access to an S3 bucket must come strictly from any of these internal VPC endpoints — no direct internet or other network access allowed. You have been tasked to write a bucket policy that accomplishes this.

The Requirement:

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Configure an Amazon S3 bucket policy so users can access the bucket only when going through one of the designated VPC endpoints in the VPC.

The Options

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• A) Create multiple S3 bucket policies using each VPC endpoint ID in separate statements with the aws:SourceVpce key in StringNotEquals condition.
• B) Create a single S3 bucket policy that uses the aws:SourceVpc key with the VPC ID in a StringNotEquals condition.
• C) Create a single S3 bucket policy that uses the aws:SourceVpce key with a wildcard pattern (e.g., vpce*) in a StringNotEquals condition.
• D) Create a single S3 bucket policy that includes multiple aws:SourceVpce values, all listed in a single StringNotEquals condition referring to all the VPC endpoint IDs.

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Correct Answer

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D

Quick Insight: The Developer Imperative

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The key lies in applying a single bucket policy that lists all authorized VPC endpoint IDs collectively using the aws:SourceVpce condition key within a StringNotEquals or StringEquals logic. This tightly restricts access only to requests originating from those specific endpoints, preventing bypass. Avoid using wildcards or separate policies which either broaden access unintentionally or complicate management.

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 D

The Winning Logic

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Amazon S3 supports the aws:SourceVpce condition key in bucket policies specifically for allowing or denying requests based on the VPC endpoint making the request. To enforce access only through specific VPC endpoints:

• Use a single bucket policy statement to improve manageability.
• Use aws:SourceVpce with a list of all allowed VPC endpoint IDs.
• Use StringNotEquals or StringEquals conditions carefully — commonly, a StringNotEquals with a NotPrincipal denies access except from listed endpoints.

This method directly ties the access control to the exact endpoint IDs, ensuring requests must flow through those controlled, private gateway endpoints. Using multiple policies (Option A) is unnecessary and cumbersome. The aws:SourceVpc key (Option B) is unsupported for S3 bucket policies and applies differently. Using wildcards (Option C) risks unintended access as aws:SourceVpce expects explicit endpoint IDs.

The Trap (Distractor Analysis):

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• Why not A? Multiple policies complicate management and can cause inconsistent enforcement.
• Why not B? aws:SourceVpc is not a valid condition key for S3 bucket policies; it won’t restrict access correctly.
• Why not C? Wildcards in aws:SourceVpce conditions are not supported and result in policy errors or open access.

The Technical Blueprint

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{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "AllowVpcEndpointAccessOnly",
      "Effect": "Deny",
      "Principal": "*",
      "Action": "s3:*",
      "Resource": [
        "arn:aws:s3:::streamline-secure-bucket",
        "arn:aws:s3:::streamline-secure-bucket/*"
      ],
      "Condition": {
        "StringNotEquals": {
          "aws:SourceVpce": [
            "vpce-0123456789abcdef0",
            "vpce-0fedcba9876543210",
            "vpce-0a1b2c3d4e5f67890"
          ]
        }
      }
    }
  ]
}

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 aws:SourceVpce with a list of allowed endpoint IDs in your bucket policy.”

Real World

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“In reality, companies often combine this with other controls like IAM policies and VPC flow logs for multi-layer security.”

(CTA) Stop Guessing, Start Mastering

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Disclaimer

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