CDN caching for static content in HLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

How does a CDN improve performance for static content?

Imagine you have a website serving images and CSS files globally. How does using a CDN help improve the loading speed for users?

A By requiring users to download all content from the origin server directly.

B By compressing files on the origin server before sending to users.

C By dynamically generating static content on each user request.

D By storing copies of static files closer to users in multiple locations worldwide.

💡 Hint

Think about how distance affects loading times and where files are stored.

A CDN caches static files in servers near users, reducing latency and speeding up content delivery.

❓ Architecture

intermediate

Which component is responsible for cache invalidation in a CDN setup?

In a CDN architecture for static content, which part typically handles cache invalidation when content updates?

A CDN edge servers automatically detect changes without any signals.

B The origin server sends cache purge requests to CDN edge servers.

C Users manually clear their browser cache to update content.

D DNS servers update cache entries for static files.

💡 Hint

Consider who controls the original content and how updates propagate.

The origin server notifies CDN edge servers to remove or refresh cached content when updates happen.

❓ scaling

advanced

What is the main benefit of using a CDN for scaling static content delivery during traffic spikes?

Your website experiences sudden high traffic. How does a CDN help handle this increased load for static files?

A By increasing the origin server's CPU and memory automatically.

B By storing static content only on the origin server to avoid duplication.

C By distributing requests across many edge servers, reducing load on the origin server.

D By blocking excess user requests to limit traffic.

💡 Hint

Think about how spreading work helps handle more users.

CDNs spread user requests to many servers worldwide, preventing overload on the origin server during spikes.

❓ tradeoff

advanced

What is a tradeoff when setting a very long cache expiration time for static content in a CDN?

Setting a long cache expiration time improves performance but what is a potential downside?

A Users may see outdated content if the origin updates but CDN cache is not refreshed.

B The CDN will consume more bandwidth from the origin server.

C The origin server will have to handle more requests directly.

D Static content will load slower for users globally.

💡 Hint

Think about content freshness versus speed.

Long cache times mean cached content stays longer, so updates may not appear immediately to users.

❓ estimation

expert

Estimate the bandwidth savings when using a CDN caching 90% of static content requests for a website serving 1TB/month of static files.

Your website serves 1TB of static files monthly. If the CDN cache hit ratio is 90%, how much bandwidth is saved on the origin server?

A 900 GB saved, only 100 GB served by origin.

B 100 GB saved, 900 GB served by origin.

C 1 TB saved, origin serves 0 GB.

D No bandwidth saved, origin serves full 1 TB.

💡 Hint

Calculate based on percentage of requests served by CDN cache.

90% cache hit means 90% of data served by CDN edges, saving that bandwidth on origin.