Content Delivery Networks (CDN) in Computer Networks - Mini Project: Build & Apply

Understanding Content Delivery Networks (CDN)

📖 Scenario: You are a network engineer learning how CDNs reduce latency by caching content at edge servers close to users. You will build a simple model of a CDN using Python dictionaries to represent edge servers, their caches, and the content delivery process.In this project, you will create the CDN infrastructure, simulate cache lookups, handle cache misses by fetching from origin, and track cache hit rates.

🎯 Goal: Build a basic data structure that models CDN edge servers, their cached content, origin server content, and a function to simulate the content delivery process with cache hit/miss tracking.

📋 What You'll Learn

Create a dictionary representing the origin server's content library

Create a dictionary representing CDN edge servers and their cached content

Implement logic to handle content requests with cache hit and miss tracking

Complete the model by calculating the cache hit rate

💡 Why This Matters

🌍 Real World

CDNs power content delivery for every major website. Understanding cache hit rates and edge server behavior is essential for optimizing performance and reducing origin server costs.

💼 Career

Network engineers and web developers use CDN metrics like cache hit rate to diagnose performance issues and optimize content delivery strategies.

1

Create the origin server content library

Create a dictionary called origin_server with these exact entries: 'index.html' with value 'Welcome Page', 'style.css' with value 'Body Styles', 'logo.png' with value 'Company Logo', and 'app.js' with value 'Application Script'.

Computer Networks

# Create the origin_server dictionary with content
# Your code here

Hint

Think of the origin server as a dictionary where each key is a filename and each value is the content it holds.

2

Create CDN edge servers with partial caches

Create a dictionary called edge_servers with two edge servers. 'edge_us' has a cache containing 'index.html' with value 'Welcome Page' and 'style.css' with value 'Body Styles'. 'edge_eu' has a cache containing only 'logo.png' with value 'Company Logo'.

Computer Networks

origin_server = {
    'index.html': 'Welcome Page',
    'style.css': 'Body Styles',
    'logo.png': 'Company Logo',
    'app.js': 'Application Script'
}
# Create edge_servers dictionary with cached content
# Your code here

Hint

Each edge server has its own cache dictionary. Not all content is cached at every edge — this is realistic CDN behavior.

3

Simulate content requests with cache tracking

Create two counter variables cache_hits and cache_misses, both set to 0. Create a list called requests with these tuples: ('edge_us', 'index.html'), ('edge_us', 'app.js'), ('edge_eu', 'logo.png'), ('edge_eu', 'style.css'). Use a for loop with variables server and file to iterate over requests. Inside the loop, check if file is in edge_servers[server]. If yes, increment cache_hits. If no, increment cache_misses and add the content from origin_server to the edge cache.

Computer Networks

origin_server = {
    'index.html': 'Welcome Page',
    'style.css': 'Body Styles',
    'logo.png': 'Company Logo',
    'app.js': 'Application Script'
}
edge_servers = {
    'edge_us': {'index.html': 'Welcome Page', 'style.css': 'Body Styles'},
    'edge_eu': {'logo.png': 'Company Logo'}
}
# Create counters, requests list, and process with a for loop
# Your code here

Hint

On a cache miss, the edge fetches from origin and stores it locally. This models how CDN caches warm up over time.

4

Calculate and store the cache hit rate

Create a variable called total_requests set to cache_hits + cache_misses. Create a variable called hit_rate set to cache_hits / total_requests.

Computer Networks

cache_hits = 0
cache_misses = 0
requests = [('edge_us', 'index.html'), ('edge_us', 'app.js'), ('edge_eu', 'logo.png'), ('edge_eu', 'style.css')]
for server, file in requests:
    if file in edge_servers[server]:
        cache_hits += 1
    else:
        cache_misses += 1
        edge_servers[server][file] = origin_server[file]
# Calculate total_requests and hit_rate
# Your code here

Hint

The hit rate shows what percentage of requests were served from cache. A higher hit rate means less load on the origin server.

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