Ruby on Rails Case Studies & Practical Application 5

Question 1

A Rails app's Lighthouse score shows a 4-second LCP. The hero image is a 3MB PNG. Best Rails-side fix?

Accepted Answer

Use Active Storage variants to serve resized, compressed WebP images

Answer

Active Storage variants transform images on demand to appropriate sizes and modern formats like WebP, drastically reducing payload.

Question 2

A Rails app's logs show 'connection pool timeout' errors under load. What does this indicate and how do you fix it?

Accepted Answer

More threads are requesting DB connections than the pool size allows; align pool size with thread count

Answer

Pool timeout means all pool connections are in use; align database.yml pool size with Puma thread count.

Question 3

A public-facing Rails API returns 500 errors when clients send a string where an integer is expected. Best fix?

Accepted Answer

Validate and coerce params using a schema object before passing to the model

Answer

Explicit schema validation at the controller boundary rejects malformed input early with a clean 422 response.

Question 4

A Rails app must generate PDF invoices for thousands of orders. Running wkhtmltopdf synchronously times out. Correct approach?

Accepted Answer

Generate PDFs in a background job and store via Active Storage; serve a download link when ready

Answer

Async generation with Active Storage decouples PDF creation from the HTTP request, providing a scalable, non-blocking user experience.

Question 5

Your Rails app has a complex discount calculation used in both the order total and the cart summary. Where should this logic live?

Accepted Answer

In a service object or model method called from both controllers

Answer

A service object or model method centralizes the logic, making it testable and preventing duplication across controllers.

Ruby on Rails Practice Test