System Design Interview Preparation: Content Delivery Networks (CDNs)

Systems design is an important concept in technical interviews at FAANG and tier-1 companies. These interviews mostly take place during the onsite rounds that follow the technical phone screen round. Systems design interviews are usually more important when hiring for senior developer and engineering management positions. They carry more weight than coding interviews while making a hiring decision. However, candidates are also expected to be good at DSA and algorithms. 

In this article, we’ll look at content delivery networks (CDNs) for systems design interviews. We’ll understand what they are, the various functions associated with these networks, and the type of interview questions to expect at design interviews. 

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Here’s what we’ll cover in this piece:

  • What are CDNs
  • Push and Pull CDNs
  • Popular Content Delivery Networks
  • Content Distribution Networks Interview Questions for Design Interviews
  • FAQs

What Are CDNs?

Content distribution networks (or content delivery networks) is a network of proxy servers and data centers that locate them. The main function of CDNs is to ensure that server performance is maintained at scale. They are extremely crucial in reducing latency while fetching static assets from a particular server. 

A content distribution network can have a huge network of servers that often spreads out globally across data centers. CDNs reduce latency and load times by keeping users close to a CDN, regardless of how far away they are from the actual server. With content distribution networks, static assets which mostly include videos, photos, and web pages coded in HTML/CSS/Javascript, aren’t fetched directly. Instead, users can access a cached copy of the assets. This massively reduces request latency and boosts server performance and also saves huge amounts of network bandwidth. 

Push and Pull CDNs

Push and pull CDNs are the two main CDN functions to populate a CDN cache. In a push CDN, engineers will have to push files to the CDN when a user makes a request. A pull CDN network will automatically fetch the static asset from the origin server in case the file isn’t present when the user makes a request. 

In a push CDN, if the origin server sends an asset, the CDN saves it in its cache and doesn't fetch the asset again when the user places a request. 

Both push and pull CDNs come with their own set of advantages and disadvantages. 

In a push CDN, developers have to constantly push files to make sure the assets are up to date. If it isn’t updated, the user won’t be able to fetch the asset when he/she makes a request. With pull CDNs, engineers don’t have to constantly push files, thereby requiring lesser maintenance. 

Pull CDNs are more popular these days than push CDNs. That’s primarily because pull CDNs are much easier to maintain given the way they operate and function. There is a disadvantage associated with pull CDNs - assets become stale after a point and users cannot fetch the updated version of the asset if the cache isn’t updated. Usually, pull CDNs attach a timestamp with the asset and cache an asset for 24 hours (default period). Pull CDNs also support cache-control headers and offer more flexibility concerning caching assets.  

Popular Content Delivery Networks

 Most cloud computing companies have their own CDNs, mostly because they can integrate these CDNs with their service offerings. Below are some popular CDNs that are operated by cloud and computing companies including Amazon, Oracle, and Microsoft, among others.

  • Azure CDN
  • AWS Cloudfront
  • Cloudflare CDN
  • Oracle CDN
  • GCP Cloud CDN

Content Distribution Networks Interview Questions for Systems Design Interviews

For systems design interviews, content delivery systems is a popular topic around which questions are commonly asked. Being adept with the popular types of CDNs, their architecture, and how they work is essential if you wish to ace design interviews at top firms.   

Below are some sample questions on CDNs for systems design interviews

  1. Explain how Google uses CDNs in its services
  2. How do CDNs work on gaming platforms?
  3. Explain how caching takes place in CDNs with an example
  4. What are some advantages of using static Javascript files?
  5. Explain the difference between push and pull CDNs
  6. What are CDN edge servers?
  7. When is it ideal to use cache busting?
  8. What is a CDN origin server?

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FAQs on Tech Interviews

1. What are the important systems design concepts that appear in technical interviews at FAANG companies?

The important topics to cover for design interviews at FAANG and tier-1 companies are scalable systems, concurrency, API modeling, sharding and caching, content delivery networks, databases, network protocols and security, replication, and measuring system performance.

2.  What coding topics are important for technical interviews at FAANG companies?

The important coding topics for technical interviews include sorting algorithms, hashing, recursion, arrays, strings, linked lists, graphs, trees, and dynamic programming.

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