Learn how to use Lambda@Edge to sort query string parameters by name and force them to be lowercase, increasing the cache hit ratio in Amazon CloudFront.
Table of Contents
Question
A company has a complex web application that leverages Amazon CloudFront for global scalability and performance. Over time, users report that the web application is slowing down.
The company’s operations team reports that the CloudFront cache hit ratio has been dropping steadily. The cache metrics report indicates that query strings on some URLs are inconsistently ordered and are specified sometimes in mixed-case letters and sometimes in lowercase letters.
Which set of actions should the solutions architect take to increase the cache hit ratio as quickly as possible?
A. Deploy a Lambda@Edge function to sort parameters by name and force them to be lowercase. Select the CloudFront viewer request trigger to invoke the function.
B. Update the CloudFront distribution to disable caching based on query string parameters.
C. Deploy a reverse proxy after the load balancer to post-process the emitted URLs in the application to force the URL strings to be lowercase.
D. Update the CloudFront distribution to specify casing-insensitive query string processing.
Answer
A. Deploy a Lambda@Edge function to sort parameters by name and force them to be lowercase. Select the CloudFront viewer request trigger to invoke the function.
Explanation
The issue described in the question is related to the inconsistent ordering and casing of query strings in the URLs, which can result in a lower cache hit ratio in CloudFront. To increase the cache hit ratio as quickly as possible, the best solution is to deploy a Lambda@Edge function to sort parameters by name and force them to be lowercase.
Lambda@Edge allows running custom code in response to CloudFront events, such as viewer requests, without provisioning or managing any infrastructure. By deploying a Lambda@Edge function with the CloudFront viewer request trigger, the function can intercept the request before it reaches the origin and modify the request headers or query strings as needed.
In this case, the Lambda@Edge function can sort the query string parameters by name and force them to be lowercase, ensuring consistent ordering and casing. This will allow CloudFront to cache the responses more effectively and reduce the number of requests that need to be forwarded to the origin.
Option B is not the best solution because disabling caching based on query string parameters will increase the cache hit ratio but will also reduce the benefits of using CloudFront as a CDN. It will result in more requests being forwarded to the origin, which can increase the response time and cost.
Option C is not the best solution because deploying a reverse proxy after the load balancer will add an additional layer of complexity and latency to the system. It will also require additional resources and maintenance.
Option D is not the best solution because specifying casing-insensitive query string processing will not solve the issue of inconsistent ordering of query string parameters. It will only allow CloudFront to match the query strings regardless of the case.
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