DVA-C02 Troubleshooting and Optimization Practice Question
A developer is using Amazon CloudFront to distribute content from an S3 bucket. The bucket is configured as an origin with Origin Access Control (OAC). Recently, some users have reported that they receive 403 Forbidden errors when accessing certain objects. The developer checks the CloudFront distribution and confirms that the OAC is set up correctly. The S3 bucket policy allows the CloudFront service principal to get objects. The developer also notes that the objects in question have been updated recently. What is the MOST likely cause of the 403 errors?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The objects are encrypted with SSE-C (server-side encryption with customer-provided keys).
The most likely cause is that the objects are encrypted with SSE-C. CloudFront cannot serve objects encrypted with SSE-C because it does not have the encryption key. When CloudFront requests such objects from S3, S3 returns a 403 Forbidden error. The other options are incorrect: Option B is wrong because the OAC is correctly configured; Option C is wrong because the bucket policy allows the CloudFront service principal; Option D is wrong because using the S3 website endpoint would not cause a 403 for encrypted objects—it would cause a different error or redirect.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The objects are encrypted with SSE-C (server-side encryption with customer-provided keys).
Why this is correct
CloudFront cannot retrieve objects encrypted with SSE-C (Server-Side Encryption with Customer-Provided Keys) because it does not have a mechanism to store or pass the customer-provided encryption key to Amazon S3 during the object retrieval request. When CloudFront attempts to fetch such an object, S3 requires the encryption key as part of the request for decryption. Without the key, S3 denies access, resulting in a 403 Forbidden error, making SSE-C fundamentally incompatible with CloudFront's caching and distribution model.
- ✗
The OAC configuration is not correctly associated with the CloudFront distribution.
Why it's wrong here
If the Origin Access Control (OAC) configuration were not correctly associated with the CloudFront distribution, CloudFront's requests to the S3 bucket would lack the necessary authorization credentials. S3 would then reject these unauthorized requests, leading to 403 Forbidden errors. However, the problem statement explicitly confirms that OAC is set up correctly, ruling out this common misconfiguration as the cause in this specific scenario.
- ✗
The S3 bucket policy denies access to the CloudFront service principal.
Why it's wrong here
An S3 bucket policy is a critical access control mechanism. If the policy explicitly denied access to the CloudFront service principal, which is identified via the OAC's associated IAM role, S3 would correctly enforce this denial by returning 403 Forbidden errors for all CloudFront requests. However, the problem statement indicates that the bucket policy *does* allow access, meaning the issue lies elsewhere and not with a restrictive bucket policy.
- ✗
The CloudFront distribution is configured to use the S3 website endpoint instead of the REST endpoint.
Why it's wrong here
Configuring a CloudFront distribution to use the S3 website endpoint (e.g., `bucket-name.s3-website.region.amazonaws.com`) instead of the S3 REST API endpoint (e.g., `bucket-name.s3.region.amazonaws.com`) would indeed prevent Origin Access Control (OAC) from functioning, as OAC is designed for the REST endpoint. While this misconfiguration could lead to access issues if the bucket is not publicly accessible, it typically manifests differently or alongside other errors, and it would not specifically cause a 403 due to an SSE-C incompatibility, which is a distinct object-level encryption problem.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DVA-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DVA-C02 exam.