SOA-C03 practice question: CloudFront and Global Accelerator (1 of 2)

Networking and Content Delivery A free question from our original SOA-C03 practice exam. Try it, then open the answer to see why each option is right or wrong.

A solar installer's marketing site uses Amazon CloudFront in front of an Application Load Balancer. Since a new ad campaign started, the cache hit ratio has fallen from 90 percent to 15 percent and origin load has risen. Every campaign link adds unique utm_source and click-ID query strings. The site's pages vary only by the lang query string. The distribution's cache policy currently includes all query strings in the cache key. What should a CloudOps engineer do?

Choose one answer.

A. Create an invalidation for /* every hour so that the caches are refreshed with the latest version of each page.
B. Raise the minimum TTL in the cache policy to one day so that cached pages stay in the edge caches longer.
C. Turn on Origin Shield so that the misses caused by the campaign links are answered from the central caching layer.
D. Change the cache policy to include only the lang query string in the cache key.

Show the answer and explanation

Answer: D

A. Wrong: Invalidations remove objects from the caches, which sends even more requests to the origin. They do nothing about unique query strings creating new cache keys. Learn more: Invalidate files to remove content (opens in a new tab)
B. Wrong: A longer TTL keeps each cached object longer, but every unique click ID is still a separate cache key. Almost every request would still miss. Learn more: Manage how long content stays in the cache (expiration) (opens in a new tab)
C. Wrong: Origin Shield consolidates requests for the same cache key. Each unique click ID is still a different key, so the requests still miss and reach the origin. Learn more: Use Amazon CloudFront Origin Shield (opens in a new tab)
D. Right: Correct. Values in the cache key create separate cached objects, so unique tracking parameters make almost every request a miss. Including only lang lets all campaign visitors share cached pages. Learn more: Understand cache policies (opens in a new tab)

Explanation

CloudFront caches one object per unique cache key. Query strings, headers and cookies in the cache key multiply the objects, and unique tracking parameters make every request different. Including only the values that change the response, here lang, restores the hit ratio. If the origin still needs other parameters, an origin request policy can forward them without adding them to the cache key.

SOA-C03 practice question: CloudFront and Global Accelerator (1 of 2)

Explanation

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