Purging CDN cache in Azure - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What happens when you purge a CDN cache?

When you purge a CDN cache, what is the immediate effect on the content delivery?

A The CDN permanently disables caching for the purged content, serving all requests directly from the origin.

B The CDN compresses the cached content to save space but continues serving it without contacting the origin.

C The cached content is deleted from all CDN edge servers, forcing fresh content retrieval from the origin on next request.

D The CDN redirects all requests for the purged content to a backup CDN provider.

💡 Hint

Think about what 'purging' means in terms of cached data.

Purging removes cached copies from CDN edge servers so that the next request fetches fresh content from the origin server.

❓ Architecture

intermediate

Designing a system to purge CDN cache efficiently

You need to design a system that triggers CDN cache purges automatically when content updates occur. Which architecture best supports this?

A A webhook from the content management system triggers a serverless function that calls the CDN purge API for updated content paths.

B A scheduled batch job runs daily to purge the entire CDN cache regardless of content changes.

C Users manually submit purge requests through a web portal after content updates.

D The CDN is configured to never cache content, so no purge system is needed.

💡 Hint

Consider automation and minimizing unnecessary purges.

Using webhooks and serverless functions allows immediate, targeted purges only for updated content, improving efficiency.

❓ scaling

advanced

Handling large-scale CDN cache purges

Your application serves millions of users globally and updates content frequently. What is the best approach to scale CDN cache purging without causing performance issues?

A Batch purge requests by grouping updated URLs and rate-limit purge API calls to avoid CDN overload.

B Purge the entire CDN cache every time any content changes to ensure freshness.

C Disable CDN caching during high update periods to avoid purging.

D Use multiple CDN providers and purge only one at a time.

💡 Hint

Think about balancing freshness and system load.

Batching and rate-limiting purge requests prevents overwhelming the CDN and origin servers while keeping content fresh.

❓ tradeoff

advanced

Tradeoffs in purging CDN cache aggressively vs. lazily

What is a key tradeoff when choosing to purge CDN cache aggressively (immediately after every update) versus lazily (periodically)?

A Aggressive purging reduces origin load but increases stale content; lazy purging increases origin load but ensures freshness.

B Aggressive purging ensures freshest content but increases origin load; lazy purging reduces load but risks serving stale content.

C Aggressive purging disables CDN caching permanently; lazy purging disables caching temporarily.

D Aggressive purging only works with static content; lazy purging only works with dynamic content.

💡 Hint

Consider freshness versus system resource usage.

Purging immediately keeps content fresh but causes more origin requests; delaying purges reduces load but may serve outdated content.

❓ estimation

expert

Estimating purge request volume for a global CDN

Your website updates 10,000 unique content items daily. Each update requires purging the CDN cache for that item. If your CDN provider limits purge API calls to 1,000 per minute, what is the minimum time in minutes to complete all purges?

A 0.1 minutes

B 100 minutes

C 1 minute

D 10 minutes

💡 Hint

Divide total purge requests by the rate limit per minute.

10,000 items / 1,000 calls per minute = 10 minutes minimum to complete all purges.