CDN caching rules in Azure - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the primary purpose of CDN caching rules?

CDN caching rules control how content is stored and served from edge servers to improve load times and reduce origin server load.

intermediate

Explain the difference between 'Cache-Control' headers and CDN caching rules.

'Cache-Control' headers are set by the origin server to guide caching behavior, while CDN caching rules are configurations on the CDN that can override or complement these headers for better control.

beginner

What does 'TTL' mean in CDN caching rules?

TTL (Time To Live) is the duration a cached object stays in the CDN edge cache before it is considered stale and fetched again from the origin.

intermediate

How can CDN caching rules improve scalability of a web application?

By caching content closer to users, CDN caching rules reduce the number of requests to the origin server, lowering server load and improving response times during traffic spikes.

beginner

Name two common conditions used in Azure CDN caching rules.

Common conditions include matching URL path patterns and HTTP request headers to apply specific caching behaviors.

What does setting a longer TTL in CDN caching rules do?

A Forces the CDN to always fetch from origin

B Keeps content cached longer at the edge servers

C Disables caching completely

D Deletes cached content immediately

A longer TTL means cached content stays longer at edge servers before refreshing.

Which header can Azure CDN caching rules override?

A Cache-Control

B Content-Type

C Authorization

D User-Agent

Azure CDN caching rules can override Cache-Control headers to customize caching.

What is a benefit of using path-based caching rules in Azure CDN?

A Different cache durations for different URL paths

B Disabling HTTPS

C Changing server IP addresses

D Blocking user access

Path-based rules allow setting different caching policies per URL path.

If content changes frequently, what caching strategy is best?

A Long TTL

B Cache forever

C Short TTL or no caching

D Disable origin server

Short TTL ensures fresh content by frequently updating cache.

Which Azure CDN feature helps to purge cached content immediately?

A Geo-filtering

B Load balancing

C SSL termination

D Content purge

Content purge removes cached content from CDN edge servers instantly.

Describe how CDN caching rules work in Azure and why they are important for web performance.

Think about how caching saves time and resources.

Explain how you would configure caching rules for a website with both static images and frequently updated news articles.

Consider content type and update frequency.

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