Content Delivery Networks (CDN) in Computer Networks - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Architecture

intermediate

CDN Architecture Components

Which component in a CDN is primarily responsible for storing cached content close to users to reduce latency?

A Origin Server

B Load Balancer

C DNS Resolver

D Edge Server

💡 Hint

Think about which part of the CDN is physically near the user.

Edge servers cache content near users to reduce latency and improve load times. Origin servers hold the original content, load balancers distribute traffic, and DNS resolvers translate domain names.

❓ scaling

intermediate

Scaling CDN for Global Traffic

When a CDN experiences a sudden global spike in traffic, which strategy best helps maintain performance?

A Deploy additional edge servers in multiple regions

B Add more origin servers in one region

C Reduce the number of edge servers to save resources

D Increase cache expiration time on edge servers

💡 Hint

Think about distributing load closer to users worldwide.

Deploying more edge servers globally distributes traffic and reduces latency. Adding origin servers in one region doesn't help global users, increasing cache time may cause stale content, and reducing edge servers worsens performance.

❓ tradeoff

advanced

Cache Expiration Tradeoff

What is the main tradeoff when setting a very short cache expiration time on CDN edge servers?

A More stale content but less bandwidth usage

B Higher latency but lower origin server load

C Lower latency but higher origin server load

D Less cache storage but more cache hits

💡 Hint

Consider how often edge servers must fetch fresh content.

Short cache expiration means edge servers refresh content often, reducing latency for fresh content but increasing load on origin servers. Longer expiration reduces origin load but risks stale content.

🧠 Conceptual

advanced

CDN Request Flow

In a typical CDN request flow, what happens if the requested content is not found in the edge server cache?

A The edge server fetches the content from the origin server

B The edge server returns a 404 error immediately

C The DNS resolver redirects the request to another edge server

D The client retries the request after a delay

💡 Hint

Think about how the CDN obtains content not locally cached.

If the edge server cache misses, it fetches the content from the origin server, caches it, and then serves it to the client. It does not return an error or rely on DNS or client retries.

❓ estimation

expert

Estimating CDN Capacity

A CDN edge server handles 10,000 requests per second, each averaging 500 KB. Estimate the minimum network bandwidth in Gbps required to support this load without congestion.

A 50 Gbps

B 40 Gbps

C 80 Gbps

D 100 Gbps

💡 Hint

Calculate total data per second and convert bytes to bits.

10,000 requests/sec * 500 KB = 5,000,000 KB/sec = 5 GB/sec. 5 GB/sec * 8 (bits/byte) = 40 Gbps minimum bandwidth.

Practice

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

easy

A. To create new content for websites

B. To store copies of content on multiple servers worldwide to speed up delivery

C. To replace the main server completely

D. To encrypt all website data end-to-end

Solution

1. Step 1: Understand CDN's role in content delivery

   A CDN stores copies of website content on servers around the world to reduce the distance data travels.

2. Step 2: Identify the main benefit of CDN

   This reduces load on the main server and speeds up content delivery to users globally.

3. Final Answer:

   To store copies of content on multiple servers worldwide to speed up delivery -> Option B

4. Quick Check:

   CDN purpose = content caching and faster delivery [OK]

Hint: CDNs cache content globally to speed up access [OK]

Common Mistakes:

• Thinking CDN creates new content
• Believing CDN replaces main server
• Confusing CDN with encryption service

2. Which of the following is a correct characteristic of a CDN's edge server?

easy

A. It stores original content only at the main data center

B. It processes all user authentication requests

C. It replaces the DNS server for domain resolution

D. It caches content closer to users to reduce latency

Solution

1. Step 1: Define edge server role in CDN

   Edge servers cache content near users to reduce the time it takes to load data.

2. Step 2: Eliminate incorrect options

   Edge servers do not store only original content, handle authentication, or replace DNS servers.

3. Final Answer:

   It caches content closer to users to reduce latency -> Option D

4. Quick Check:

   Edge server = caches content near users [OK]

Hint: Edge servers cache content near users for speed [OK]

Common Mistakes:

• Confusing edge servers with main data center
• Assuming edge servers handle authentication
• Thinking edge servers replace DNS

3. Consider a CDN setup where a user requests a video file. The CDN edge server does not have the file cached. What happens next?

medium

A. The edge server redirects the user to another edge server

B. The edge server returns an error to the user immediately

C. The edge server fetches the file from the origin server and caches it

D. The edge server compresses the request and sends it back

Solution

1. Step 1: Understand cache miss in CDN

   If the edge server does not have the requested content, it must get it from the origin server.

2. Step 2: Describe caching after fetch

   After fetching, the edge server caches the content to serve future requests faster.

3. Final Answer:

   The edge server fetches the file from the origin server and caches it -> Option C

4. Quick Check:

   Cache miss = fetch from origin + cache [OK]

Hint: Cache miss triggers fetch from origin and caching [OK]

Common Mistakes:

• Thinking edge server returns error on cache miss
• Assuming user is redirected to another edge server
• Believing edge server compresses request instead

4. A CDN is configured but users report slow loading times from certain regions. What is the most likely cause?

medium

A. The CDN has no edge servers near those regions

B. The origin server is down globally

C. Users have slow internet unrelated to CDN

D. The CDN is encrypting content too much

Solution

1. Step 1: Analyze CDN coverage impact

   If edge servers are missing near certain regions, content must travel farther, causing delays.

2. Step 2: Rule out other causes

   Origin server down affects all users, slow internet is user-side, and encryption does not cause major delays.

3. Final Answer:

   The CDN has no edge servers near those regions -> Option A

4. Quick Check:

   Missing edge servers = slow regional load [OK]

Hint: No local edge servers cause regional slowness [OK]

Common Mistakes:

• Blaming origin server when issue is regional
• Ignoring CDN edge server distribution
• Assuming encryption causes slow loading

5. You are designing a CDN for a global video streaming service. Which combination of strategies will best improve performance and scalability?

hard

A. Use many edge servers worldwide and implement cache invalidation policies

B. Use a single large origin server and no caching at edges

C. Only cache static images and stream videos directly from origin

D. Disable caching and rely on user devices to store content

Solution

1. Step 1: Identify key CDN strategies for video streaming

   Many edge servers reduce latency globally; cache invalidation keeps content fresh.

2. Step 2: Evaluate other options

   Single origin server causes bottlenecks; no caching wastes bandwidth; disabling caching hurts performance.

3. Final Answer:

   Use many edge servers worldwide and implement cache invalidation policies -> Option A

4. Quick Check:

   Global edges + cache control = best scalability [OK]

Hint: Global edges plus cache policies boost CDN performance [OK]

Common Mistakes:

• Relying on single origin server only
• Not caching large video files
• Disabling caching entirely