Content delivery with CDN in HLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Architecture

intermediate

Designing a CDN for Global Content Delivery

You need to design a Content Delivery Network (CDN) to serve static images globally with low latency. Which architectural component is essential to reduce the load on the origin server?

A Direct user requests always routed to the origin server

B A single centralized database to store all images

C Edge cache servers located near users to store and serve cached content

D Load balancer only at the origin server without caching

💡 Hint

Think about how to reduce repeated requests to the main server by serving content closer to users.

Edge cache servers store copies of content near users, reducing latency and origin server load. Other options do not reduce load or latency effectively.

❓ scaling

intermediate

Handling Traffic Spikes with CDN

Your CDN experiences sudden traffic spikes during a product launch. Which scaling strategy helps maintain performance without overloading origin servers?

A Increase cache TTL to keep content longer at edge servers

B Disable caching to always fetch fresh content from origin

C Reduce the number of edge servers to concentrate traffic

D Route all traffic through a single data center

💡 Hint

Consider how caching duration affects origin server load during high traffic.

Increasing cache TTL keeps content longer at edge servers, reducing origin requests during spikes. Disabling caching or reducing edge servers increases load and latency.

❓ tradeoff

advanced

Tradeoff Between Cache Freshness and Latency

In a CDN, what is the main tradeoff when setting a very short cache expiration time (TTL) for dynamic content?

A Lower latency but higher origin server load due to frequent cache misses

B Higher latency and lower origin server load

C No impact on latency or origin server load

D Cache never expires, so content is always stale

💡 Hint

Think about how often the CDN must fetch fresh content from the origin.

Short TTL causes frequent cache expiration, increasing origin requests and load, but ensures fresher content with lower latency for cache hits.

🧠 Conceptual

advanced

Understanding CDN Request Flow

When a user requests a file from a CDN edge server that does not have the file cached, what is the correct sequence of events?

A 2,1,3,4

B 1,2,3,4

C 1,3,2,4

D 3,2,1,4

💡 Hint

Think about the logical order from cache check to serving the user.

The edge server first checks cache (1). On miss, it requests origin (2). Origin responds (3). Edge caches and serves (4).

❓ estimation

expert

Estimating CDN Capacity for Video Streaming

You expect 1 million users streaming a 5-minute video simultaneously via CDN. Each video bitrate is 3 Mbps. Estimate the minimum total bandwidth capacity the CDN must support to serve all users without buffering.

A Approximately 1,000 Gbps

B Approximately 500 Gbps

C Approximately 15,000 Gbps

D Approximately 3,000 Gbps

💡 Hint

Calculate total bandwidth by multiplying users by bitrate, then convert units carefully.

1,000,000 users × 3 Mbps = 3,000,000 Mbps = 3,000 Gbps (1 Gbps = 1,000 Mbps). The CDN must support at least 3,000 Gbps (B).