CDN caching rules in Azure - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

How does CDN caching improve website performance?

Imagine you have a website with visitors all over the world. How does using a CDN caching rule help improve the speed of your website?

A By storing copies of website content closer to users, reducing load times.

B By increasing the size of the website files to make them load slower.

C By forcing all users to access the original server directly every time.

D By disabling all caching to ensure fresh content always loads.

💡 Hint

Think about how distance affects how fast data travels on the internet.

CDNs cache content near users, so data travels a shorter distance, making websites load faster.

❓ Architecture

intermediate

Which Azure CDN caching rule setup best handles frequently updated images?

You have images on your website that update every hour. Which caching rule setup ensures users see fresh images but still benefits from caching?

A Disable caching for images completely.

B Set cache duration to 24 hours with no revalidation.

C Set cache duration to 1 hour and enable cache revalidation.

D Set cache duration to 1 week to reduce server load.

💡 Hint

Consider how often the images change and how caching duration affects freshness.

Setting cache duration to 1 hour matches the update frequency, and revalidation ensures freshness.

❓ scaling

advanced

How does Azure CDN caching rules affect scalability during traffic spikes?

Your website experiences sudden traffic spikes. How do CDN caching rules help maintain performance and scalability?

A By serving cached content from edge locations, reducing origin server load.

B By sending all requests to the origin server to ensure fresh data.

C By disabling caching to force real-time data delivery.

D By limiting the number of users who can access the site simultaneously.

💡 Hint

Think about how caching reduces work for the main server during high demand.

Cached content served from CDN edges reduces origin server load, helping handle more users smoothly.

❓ tradeoff

advanced

What is a tradeoff when setting very long cache durations in Azure CDN caching rules?

Choosing a very long cache duration can improve performance but may cause what issue?

A The origin server will receive more requests.

B Users may see outdated content until cache expires.

C The CDN will use more bandwidth than usual.

D Cache will refresh too frequently, increasing latency.

💡 Hint

Think about how caching duration affects content freshness.

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

❓ estimation

expert

Estimate the cache hit ratio impact when enabling Azure CDN caching for static assets

Your website serves 1 million requests per day. 70% are for static assets like images and scripts. If Azure CDN caching is enabled with proper rules, what is the expected cache hit ratio and how many requests will reach the origin server?

A Cache hit ratio ~30%, so about 700,000 requests reach origin.

B Cache hit ratio ~50%, so about 500,000 requests reach origin.

C Cache hit ratio ~95%, so about 50,000 requests reach origin.

D Cache hit ratio ~85%, so about 150,000 requests reach origin.

💡 Hint

Consider that static assets are highly cacheable and most requests for them will be served by CDN.

With 70% static requests and good caching, about 85% of total requests hit cache, leaving 15% (150,000) to origin.

Practice

1. What is the primary purpose of CDN caching rules in Azure CDN?

easy

A. To monitor server CPU usage

B. To encrypt data between client and server

C. To control how content is stored and served from CDN servers

D. To manage user authentication

Solution

1. Step 1: Understand CDN caching rules

   CDN caching rules define how content is cached and delivered by CDN servers.

2. Step 2: Identify the main goal

   The main goal is to improve speed and reduce load by controlling content storage and delivery.

3. Final Answer:

   To control how content is stored and served from CDN servers -> Option C

4. Quick Check:

   CDN caching rules = control content caching [OK]

Hint: Caching rules control content storage and delivery [OK]

Common Mistakes:

• Confusing caching with encryption
• Thinking caching manages authentication
• Assuming caching monitors server CPU

2. Which Azure CDN caching rule syntax correctly sets a cache duration of 3600 seconds for all images?

easy

A. cache-duration: 3600; match: *.jpg, *.png

B. cache-control: max-age=3600; match: *.jpg, *.png

C. cache-control: max-age=3600; match: images/*

D. cache-duration: max-age=3600; match: images/*

Solution

1. Step 1: Identify correct cache-control syntax

   Azure CDN uses 'cache-control: max-age=seconds' to set cache duration.

2. Step 2: Match correct file patterns

   Images are matched by extensions like '*.jpg, *.png' not 'images/*'.

3. Final Answer:

   cache-control: max-age=3600; match: *.jpg, *.png -> Option B

4. Quick Check:

   cache-control max-age + correct pattern = cache-control: max-age=3600; match: *.jpg, *.png [OK]

Hint: Use 'cache-control: max-age' with file extensions for images [OK]

Common Mistakes:

• Using 'cache-duration' instead of 'cache-control'
• Using folder pattern 'images/*' instead of file extensions
• Mixing syntax keywords incorrectly

3. Given this Azure CDN caching rule:
cache-control: max-age=0; match: /api/*
What will happen when a user requests /api/data?

medium

A. Content will be blocked by CDN

B. Content will be cached indefinitely

C. Content will be cached for 3600 seconds

D. Content will be cached for 0 seconds, forcing CDN to fetch fresh data every time

Solution

1. Step 1: Interpret max-age=0 meaning

   max-age=0 means no caching; content is always fresh.

2. Step 2: Apply rule to /api/* path

   Requests to /api/data match /api/*, so caching is disabled.

3. Final Answer:

   Content will be cached for 0 seconds, forcing CDN to fetch fresh data every time -> Option D

4. Quick Check:

   max-age=0 disables caching = Content will be cached for 0 seconds, forcing CDN to fetch fresh data every time [OK]

Hint: max-age=0 means no caching, always fresh content [OK]

Common Mistakes:

• Assuming max-age=0 caches content indefinitely
• Confusing path matching syntax
• Thinking content is blocked

4. You wrote this Azure CDN caching rule:
cache-control max-age=600; match: *.css
But it does not work as expected. What is the error?

medium

A. Missing colon after 'cache-control'

B. Incorrect file extension pattern

C. max-age value too low

D. Match pattern should be a full URL

Solution

1. Step 1: Check syntax for cache-control

   The correct syntax requires a colon after 'cache-control', like 'cache-control: max-age=600'.

2. Step 2: Validate other parts

   File extension '*.css' is correct; max-age=600 is valid; match pattern does not require full URL.

3. Final Answer:

   Missing colon after 'cache-control' -> Option A

4. Quick Check:

   Syntax error: missing colon = Missing colon after 'cache-control' [OK]

Hint: Remember colon after 'cache-control:' in rules [OK]

Common Mistakes:

• Omitting colon after 'cache-control'
• Using wrong file patterns
• Thinking max-age value causes failure

5. You want to optimize caching for a website with static images and dynamic API data. Which Azure CDN caching rules setup is best?

hard

A. Set cache-control: max-age=86400 for images (*.jpg, *.png) and cache-control: max-age=0 for API (/api/*)

B. Set cache-control: max-age=0 for all content

C. Set cache-control: max-age=3600 for all content

D. Set cache-control: max-age=86400 for API and cache-control: max-age=0 for images

Solution

1. Step 1: Understand content types and caching needs

   Static images benefit from long caching (86400 seconds = 1 day). Dynamic API data needs fresh content, so max-age=0.

2. Step 2: Match rules to content paths

   Apply long cache to image extensions (*.jpg, *.png) and no cache to API paths (/api/*).

3. Final Answer:

   Set cache-control: max-age=86400 for images (*.jpg, *.png) and cache-control: max-age=0 for API (/api/*) -> Option A

4. Quick Check:

   Static long cache + dynamic no cache = Set cache-control: max-age=86400 for images (*.jpg, *.png) and cache-control: max-age=0 for API (/api/*) [OK]

Hint: Long cache for static, no cache for dynamic content [OK]

Common Mistakes:

• Caching dynamic API data too long
• Not differentiating static and dynamic content
• Reversing cache durations for content types