- A
Update the CloudFront cache policy to ignore `reqId` and include only the stable `v` query string parameter in the cache key.
Because `reqId` is unique per request, including it in the cache key prevents cache reuse (each request maps to a different cache entry), resulting in frequent origin fetches. Excluding `reqId` and keeping only `v` allows many requests for the same version to share cached objects, reducing origin traffic and cost while preserving correct version behavior.
- B
Lower the CloudFront minimum TTL to 0 seconds so cached objects revalidate more often, reducing origin fetch volume.
Why wrong: Setting TTLs closer to 0 typically increases revalidation/refresh frequency and can increase origin contact. It does not address the root cause here: cache key fragmentation caused by including a unique `reqId` value.
- C
Set the S3 bucket to use compression and enable S3 Transfer Acceleration to reduce origin fetch charges.
Why wrong: The observed increase is driven by higher origin fetch *request* volume caused by poor cache key hit ratio. Compression and Transfer Acceleration may change payload size or transfer characteristics but do not fix the caching failure caused by `reqId` being part of the cache key.
- D
Disable forwarding of the query string to the origin, but keep using the full query string (including `reqId`) in the cache key.
Why wrong: Even if CloudFront does not forward query strings to the origin, the cache key still determines cache reuse. If `reqId` remains part of the cache key, CloudFront will still create mostly unique cache entries, so origin fetches remain high.
Quick Answer
The answer is to update the CloudFront cache policy to ignore the `reqId` query string and include only the stable `v` parameter in the cache key. This is correct because the `reqId` parameter is unique per request, so forwarding all query strings forces CloudFront to treat each request as a distinct cache object, defeating cache efficiency and driving up origin fetches and costs. By optimizing the cache key to include only the versioned `v` parameter, CloudFront can serve cached responses for all requests sharing the same version, drastically reducing origin load and billable transfers. On the SAA-C03 exam, this scenario tests your understanding of CloudFront cache key optimization for query string cost reduction—a common trap is assuming all query strings must be forwarded for correctness. The key insight is that only parameters affecting content (like `v`) belong in the cache key; unique identifiers like `reqId` should be ignored. Memory tip: "Keep the stable, ditch the random."
SAA-C03 Design Cost-Optimized Architectures Practice Question
This SAA-C03 practice question tests your understanding of design cost-optimized architectures. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company serves versioned images from S3 through CloudFront. After a release, CloudFront origin fetches increased sharply and the monthly CloudFront bill went up. They reviewed CloudFront logs and found that many requests include a query string parameter `reqId` that is unique per request (for example, `...?v=2026-04-01&reqId=...`). The team currently forwards all query strings to the cache key. What change is most likely to reduce origin fetches and cost while keeping the versioned images correct?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
Update the CloudFront cache policy to ignore `reqId` and include only the stable `v` query string parameter in the cache key.
Option A is correct because the `reqId` query string parameter is unique per request, which forces CloudFront to treat each request as a distinct cache object when all query strings are forwarded to the cache key. By configuring the cache policy to include only the stable `v` parameter (the version identifier) and ignore `reqId`, CloudFront can serve cached responses for all requests with the same `v` value, drastically reducing origin fetches and lowering costs. This approach preserves correct versioned image delivery because the `v` parameter still differentiates between image versions.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Update the CloudFront cache policy to ignore `reqId` and include only the stable `v` query string parameter in the cache key.
Why this is correct
Because `reqId` is unique per request, including it in the cache key prevents cache reuse (each request maps to a different cache entry), resulting in frequent origin fetches. Excluding `reqId` and keeping only `v` allows many requests for the same version to share cached objects, reducing origin traffic and cost while preserving correct version behavior.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Lower the CloudFront minimum TTL to 0 seconds so cached objects revalidate more often, reducing origin fetch volume.
Why it's wrong here
Setting TTLs closer to 0 typically increases revalidation/refresh frequency and can increase origin contact. It does not address the root cause here: cache key fragmentation caused by including a unique `reqId` value.
- ✗
Set the S3 bucket to use compression and enable S3 Transfer Acceleration to reduce origin fetch charges.
Why it's wrong here
The observed increase is driven by higher origin fetch *request* volume caused by poor cache key hit ratio. Compression and Transfer Acceleration may change payload size or transfer characteristics but do not fix the caching failure caused by `reqId` being part of the cache key.
- ✗
Disable forwarding of the query string to the origin, but keep using the full query string (including `reqId`) in the cache key.
Why it's wrong here
Even if CloudFront does not forward query strings to the origin, the cache key still determines cache reuse. If `reqId` remains part of the cache key, CloudFront will still create mostly unique cache entries, so origin fetches remain high.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think forwarding all query strings is harmless or that lowering TTL helps reduce origin fetches, but the real issue is cache key fragmentation caused by unique parameters like `reqId`.
Detailed technical explanation
How to think about this question
CloudFront cache keys are built from the request URL, including query strings when forwarding is enabled. By default, CloudFront includes all query string parameters in the cache key unless a cache policy explicitly whitelists or ignores specific parameters. The `reqId` parameter, being unique per request, creates a new cache entry for every request, leading to cache misses and origin fetches. In contrast, the `v` parameter is stable across requests for the same image version, so whitelisting only `v` ensures cache hits for all requests with the same version, while ignoring `reqId` prevents cache fragmentation. This is a common pattern for versioned static assets served through CDNs.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
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FAQ
Questions learners often ask
What does this SAA-C03 question test?
Design Cost-Optimized Architectures — This question tests Design Cost-Optimized Architectures — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Update the CloudFront cache policy to ignore `reqId` and include only the stable `v` query string parameter in the cache key. — Option A is correct because the `reqId` query string parameter is unique per request, which forces CloudFront to treat each request as a distinct cache object when all query strings are forwarded to the cache key. By configuring the cache policy to include only the stable `v` parameter (the version identifier) and ignore `reqId`, CloudFront can serve cached responses for all requests with the same `v` value, drastically reducing origin fetches and lowering costs. This approach preserves correct versioned image delivery because the `v` parameter still differentiates between image versions.
What should I do if I get this SAA-C03 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Same concept, more angles
1 more ways this is tested on SAA-C03
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A team serves static web assets (JS, CSS, images) from an Amazon S3 origin through CloudFront. Recently, the S3 origin has received a high number of requests for the same files, increasing origin data transfer costs. CloudFront access logs show many cache misses, and each request includes a unique query string used only for tracking (for example, ?utm=...). The application does not require query-string-specific content. What CloudFront change will most directly reduce origin fetches and cost?
medium- ✓ A.Update the CloudFront cache policy to exclude query strings from the cache key so that requests differing only by tracking query parameters reuse the same cached object.
- B.Lower the minimum TTL and set Cache-Control headers to no-store to force CloudFront to revalidate more often.
- C.Enable Origin Shield to ensure all origin fetches go through a single regional shield with no other configuration changes.
- D.Switch the S3 origin from S3 to a different storage class optimized for request rates, keeping the cache key the same.
Why A: Option A is correct because CloudFront's cache policy controls which parts of a request (including query strings) are included in the cache key. By excluding the tracking query strings (e.g., `?utm=...`) from the cache key, CloudFront will treat all requests for the same file as identical, serving the cached object regardless of the query string. This directly reduces the number of origin fetches (cache misses) and lowers S3 data transfer costs, as the application does not require query-string-specific content.
Last reviewed: Jun 11, 2026
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