Get Your CertSAP-C02PlayCompete
‹ All SAP-C02 questions

SAP-C02 Practice Question 27: Edge Function Cost and Latency

AWS Certified Solutions Architect – Professional (SAP-C02) · Test 3 · question 7 of 10

Continuous Improvementmedium

A news publisher serves 2.5 million requests per second at peak through Amazon CloudFront. A Lambda@Edge function on the viewer request event does two things: it rewrites legacy article paths to the current URL scheme, and it strips a dozen marketing query-string parameters so that requests for the same article share one cache entry.

Two problems have appeared. Costs for the edge function now rival the CloudFront delivery bill, and during traffic spikes the function is throttled and viewers receive errors. The rewrite and the query-string normalization must both still happen before CloudFront computes the cache key, the logic is about 40 lines of string manipulation with no calls to other services and no need to read the request body, and the team wants the change to reduce both per-request cost and added latency.

What should the solutions architect do?

Select one answer
Show answer and explanation

Answer:

  • A. Reimplement the rewrite and query-string normalization as a CloudFront function associated with the viewer request event

CloudFront Functions is purpose-built for this workload. AWS lists cache key normalization and URL rewrites as its headline use cases, it runs at viewer request and viewer response, its function duration is submillisecond, and it scales to millions of requests per second, against Lambda@Edge's limit of 10,000 requests per second per Region, which is what is throttling the publisher today. The constraints in the stem match the restrictions of CloudFront Functions exactly: pure string manipulation, no network access, and no access to the request body. It is also dramatically cheaper per invocation than Lambda@Edge, which addresses the cost problem directly.

Option B would cut invocations, but it breaks the requirement. The origin request event fires only after CloudFront has already computed the cache key and missed, so normalizing the query string there cannot consolidate cache entries, and the path rewrite would no longer influence what is cached.

Option C moves the logic behind the cache entirely. CloudFront would keep a separate cache entry per marketing parameter, so the cache hit ratio collapses and every variant reaches the origin, the opposite of the goal.

Option D treats a scaling ceiling as a tuning problem. More memory does not raise Lambda@Edge's per-Region request rate, and keeping a Lambda@Edge invocation on every one of 2.5 million requests per second leaves the cost problem exactly where it is.

Reference: Differences between CloudFront Functions and Lambda@Edge

Practice Test 3 ›

Study guides for SAP-C02

Which AWS certification should you get? 2026 roadmapWhich AWS certification to get first, by role and experience, with each exam's status in October 2026, what is changing, and prices in USD and INR.
SAP-C02 vs SAP-C03, the Solutions Architect Professional updateWhat changes when AWS replaces SAP-C02 with SAP-C03, the key dates, who should still sit SAP-C02, and how to study through the switch without wasted work.
AWS disaster recovery strategies, RTO and RPOBackup and restore, pilot light, warm standby and active/active on AWS, how RTO and RPO pick between them, and the services each strategy uses.
IAM users, roles and policies on AWSHow IAM users, roles, identity-based and resource-based policies, cross-account access, SCPs and permissions boundaries fit together for AWS exams.
SQS vs SNS vs EventBridge on AWSWhen to use an SQS queue, an SNS topic or an EventBridge bus, plus fan-out, FIFO ordering, visibility timeouts and dead-letter queues for AWS exams.
VPC endpoints vs NAT gateways on AWSWhen to use gateway endpoints, interface endpoints (PrivateLink) or a NAT gateway for private subnets, and the cost and security trade-offs exams test.