Google ACE Practice Question: A company uses Cloud CDN to accelerate content…

A company uses Cloud CDN to accelerate content delivery. They notice that some requests are not being cached, despite the cache-control headers being set correctly. The origin is a Compute Engine instance behind an HTTP load balancer. What is a likely cause?

⚠ Common exam trap

The trap here is that candidates often focus on cache-control headers or query strings, but Google Cloud tests the less obvious behavior that Set-Cookie headers implicitly prevent caching in Cloud CDN, even when other caching directives appear correct.

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 origin returns a Set-Cookie header, which prevents caching by default.

Cloud CDN will not cache responses that include a Set-Cookie header by default, even if Cache-Control headers are correctly set. This is because Set-Cookie indicates user-specific or session-specific content, and caching it could lead to serving private data to other users. The origin (Compute Engine behind an HTTP load balancer) returning Set-Cookie effectively disables caching for those responses.

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 cache key includes the query string, causing too many variations.
Why it's wrong here
Including the query string in the Cloud CDN cache key is the default behavior and creates a separate cache entry for every unique URL with different parameters. This would dramatically increase the number of cached objects and lower the cache hit ratio, but it would not prevent Cloud CDN from caching those responses entirely. Every distinct query string would still be cached independently, so this cannot explain a complete absence of cached content.
✗
The load balancer is using HTTP/2, which disables caching.
Why it's wrong here
HTTP/2 is a transport-level protocol that allows multiplexing requests over a single connection; it has no bearing on whether a response is cacheable. Cloud CDN supports HTTP/2 and continues to cache content served over it exactly as it would for HTTP/1.1. Caching behavior is determined solely by response headers and Cloud CDN configuration, not by the negotiated HTTP protocol version.
✗
The content type is not supported by Cloud CDN.
Why it's wrong here
Cloud CDN does not restrict caching based on MIME type or content type; it can cache HTML, CSS, JavaScript, images, video, and even dynamically generated content as long as the response is cacheable. The presence of some exotic content type would not prevent caching—Cloud CDN only requires that the response satisfy HTTP caching rules, such as having valid Cache-Control headers. A correctness issue like a missing content type would affect rendering, not cache behavior.
✓
The origin returns a Set-Cookie header, which prevents caching by default.
Why this is correct
When an origin includes a Set-Cookie header in a response, Cloud CDN's default cache mode treats that response as private and skips caching entirely. This prevents any user-specific response from being accidentally served to other users, and follows the principle that responses with cookies often contain personalized data. Unless you explicitly configure the cache mode to FORCE_CACHE_ALL or configure Cloud CDN to ignore Set-Cookie, the presence of Set-Cookie effectively disables caching for that response.

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Google ACE Practice Question: A company uses Cloud CDN to accelerate content…

Why each option matters

Option-by-option breakdown

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