Content delivery with CDN in HLD - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify the primary purpose of a CDN in content delivery.

HLD

A CDN primarily helps to [1] content closer to users.

Drag options to blanks, or click blank then click option'

Acache

Bdelete

Cencrypt

Dcompress

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'delete' or 'encrypt' which are unrelated to CDN's main function.

A CDN caches content on servers near users to reduce latency and improve load times.

2fill in blank

medium

Complete the code to show the step where user requests are directed to the nearest CDN server.

HLD

When a user requests content, DNS [1] directs the request to the closest CDN edge server.

Drag options to blanks, or click blank then click option'

Arouting

Bcaching

Ccompression

Dencryption

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing routing with caching or compression.

DNS routing helps direct user requests to the nearest CDN edge server for faster content delivery.

3fill in blank

hard

Fix the error in the description of CDN cache invalidation.

HLD

CDN cache invalidation is the process of [1] outdated content from edge servers.

Drag options to blanks, or click blank then click option'

Aduplicating

Bupdating

Cremoving

Dencrypting

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'updating' which is not the exact process of invalidation.

Cache invalidation means removing outdated content so fresh content can be served.

4fill in blank

hard

Fill both blanks to complete the CDN request flow correctly.

HLD

User requests content -> DNS [1] -> CDN edge server [2] content if cached -> origin server if not cached.

Drag options to blanks, or click blank then click option'

Arouting

Bcompresses

Cserves

Dencrypts

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up compression or encryption with serving content.

DNS routing directs requests; CDN edge servers serve cached content to users.

5fill in blank

hard

Fill all three blanks to complete the CDN cache control logic.

HLD

Cache-Control header: max-age=[1], must-revalidate=[2], proxy-revalidate=[3].

Drag options to blanks, or click blank then click option'

A3600

Btrue

Cfalse

D7200

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing true/false values for revalidation flags.

max-age sets cache duration; must-revalidate true forces revalidation; proxy-revalidate false allows proxy caching without revalidation.

Practice

1. What is the primary purpose of a Content Delivery Network (CDN)?

easy

A. To store user data permanently

B. To cache content closer to users for faster delivery

C. To replace the origin server completely

D. To encrypt all website content

Solution

1. Step 1: Understand CDN function

   A CDN stores copies of content in multiple locations worldwide to reduce latency.

2. Step 2: Identify main benefit

   This caching near users speeds up content delivery and reduces load on the origin server.

3. Final Answer:

   To cache content closer to users for faster delivery -> Option B

4. Quick Check:

   CDN = caching near users [OK]

Hint: CDN = cache content near users for speed [OK]

Common Mistakes:

• Thinking CDN replaces origin server
• Confusing CDN with data storage
• Assuming CDN encrypts all content

2. Which of the following is the correct sequence when a user requests content served via a CDN?

easy

A. User -> Origin Server -> CDN -> User

B. Origin Server -> User -> CDN

C. User -> CDN -> Origin Server (if needed) -> CDN -> User

D. User -> CDN -> User -> Origin Server

Solution

1. Step 1: Trace request flow in CDN

   User first contacts the CDN edge server; if content is cached, it responds immediately.

2. Step 2: Understand cache miss handling

   If content is not cached, CDN fetches it from the origin server, caches it, then serves user.

3. Final Answer:

   User -> CDN -> Origin Server (if needed) -> CDN -> User -> Option C

4. Quick Check:

   Request flow = CDN first, origin fallback [OK]

Hint: User hits CDN first, origin only if cache miss [OK]

Common Mistakes:

• Assuming user contacts origin server first
• Ignoring CDN cache miss flow
• Confusing response direction

3. Consider this simplified code snippet representing a CDN cache check:

cache = {"index.html": "content"}
request = "style.css"

if request in cache:
    response = cache[request]
else:
    response = "fetch from origin"
print(response)

What will be printed?

medium

A. fetch from origin

B. KeyError

C. content

D. None

Solution

1. Step 1: Check if request key exists in cache

   The request is "style.css" which is not in cache keys (only "index.html" exists).

2. Step 2: Determine else branch execution

   Since request not found, else branch runs, setting response to "fetch from origin".

3. Final Answer:

   fetch from origin -> Option A

4. Quick Check:

   Cache miss prints fetch from origin [OK]

Hint: If key missing in cache, else branch runs [OK]

Common Mistakes:

• Assuming cache returns default value automatically
• Expecting KeyError without else
• Confusing cache keys with values

4. A CDN is configured but users report slow content loading. Which of these is the most likely cause?

medium

A. The CDN is caching all content correctly

B. Users have slow internet unrelated to CDN

C. The origin server is down but CDN cache is fresh

D. The CDN edge servers are geographically far from users

Solution

1. Step 1: Analyze CDN slow delivery causes

   If CDN edge servers are far from users, latency increases, causing slow loading.

2. Step 2: Evaluate other options

   The CDN is caching all content correctly means caching works, so unlikely cause. The origin server is down but CDN cache is fresh means cache serves content fast. Users have slow internet unrelated to CDN is user-side, not CDN issue.

3. Final Answer:

   The CDN edge servers are geographically far from users -> Option D

4. Quick Check:

   Distance to CDN edge affects speed [OK]

Hint: Far CDN edges cause slow delivery [OK]

Common Mistakes:

• Blaming origin server when cache is fresh
• Ignoring CDN server location
• Assuming caching always fixes speed

5. You want to design a CDN system that handles sudden traffic spikes without overloading the origin server. Which combination of strategies is best?

hard

A. Use aggressive caching with long TTL and multiple CDN edge locations

B. Disable caching and let all requests go to origin server

C. Use a single CDN edge server with short TTL caching

D. Serve content only from origin server with load balancer

Solution

1. Step 1: Understand traffic spike handling

   Long TTL caching reduces origin hits; multiple edges distribute load geographically.

2. Step 2: Evaluate options for scalability

   Disable caching and let all requests go to origin server and D overload origin server. Use a single CDN edge server with short TTL caching limits caching benefits and single edge risks bottleneck.

3. Final Answer:

   Use aggressive caching with long TTL and multiple CDN edge locations -> Option A

4. Quick Check:

   Long TTL + many edges = scalable CDN [OK]

Hint: Long cache + many edges handle spikes best [OK]

Common Mistakes:

• Disabling caching under traffic spikes
• Relying on single edge server
• Ignoring TTL impact on origin load