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System Design Interviews for Data Engineers: Questions and Strategies

System design interviews go beyond assessing technical know-how; they are a test of a candidate’s visionary approach to system architecture. They probe into how candidates think about data flow, handle potential bottlenecks, and anticipate future challenges and scalability issues. Interviewers are keen to see how candidates can translate complex requirements into tangible, efficient systems.

This article, drawing inspiration from the comprehensive System Design Engineer Interview course at DE Academy, is tailored to unfold the layers of system design interviews. It aims to guide data engineers, both seasoned and new, through the intricate aspects of these interviews. Our focus is on the ‘what’ and the ‘how’ of excelling in these assessments.

What Is System Design?

The goal is to create a framework where various components and modules interact seamlessly to perform functions. This design phase involves making critical decisions about the system’s architecture, the interrelationship between different parts of the system, and how these parts come together to form a cohesive unit.

Key considerations in system design include ensuring scalability to meet increased demand, maintaining consistent performance and functionality despite failures or errors, and safeguarding the system and its data against unauthorized access or breaches.

In data engineering, system design also encompasses the creation of efficient data pipelines, data storage solutions, and data processing mechanisms. This entails making decisions about data modeling, ETL processes, database design, and managing data flow throughout the system.

Core System Design  Concepts  for Data Engineers

Load Balancer

The primary function of a load balancer is to prevent any single server from getting overwhelmed by requests. This is achieved by distributing the incoming network traffic across a group of backend servers, also known as a server farm or server pool. By doing so, load balancers optimize resource use, maximize throughput, minimize response time, and avoid overload of any single resource.

Load balancers operate at various layers of the OSI model. For instance, a Layer 4 load balancer distributes traffic based on data from network and transport layer protocols, such as IP addresses and TCP ports. On the other hand, a Layer 7 load balancer, also known as an application-level load balancer, makes routing decisions based on content within the application layer, such as HTTP headers and SSL session IDs.


API Gateway

API Gateway is a fundamental component in microservices architecture, acting as a reverse proxy to accept all application programming interface (API) calls, aggregate the various services required to fulfill them and return the appropriate result. It’s a system that manages, processes, and routes API requests from clients to various microservices in the backend.

Functions of an API Gateway

  • Request Routing. The API Gateway routes incoming requests to the appropriate microservices. It’s akin to a traffic controller, determining where to send each request based on the requested path, method, and other parameters.
  • API Composition. In a microservices architecture, different functionalities are often spread across multiple services. The API Gateway can aggregate results from multiple microservices and deliver them as a unified response to the user.
  • Authentication and Authorization. It often handles the authentication and authorization of API requests, ensuring that the clients have the right credentials to access the services.
  • Rate Limiting and Throttling. API Gateways can enforce rate limits and throttling rules to manage the load on the microservices and prevent abuse.
  • Caching. By caching responses, the API Gateway can reduce the number of requests sent to microservices, thereby enhancing the response time.

Potential Challenges

  • Performance Bottlenecks. The API Gateway can become a bottleneck if not scaled properly, especially under heavy load, as all requests pass through it.
  • Complexity in Configuration. As the central point of processing API requests, the API Gateway configuration can become complex, particularly in a system with numerous services.
  • Single Point of Failure. If not architected for high availability, it can become a single point of failure, potentially impacting the entire system if it goes down.


Caching refers to the practice of storing data in a temporary storage area (the cache) so that future requests for that data can be served faster. The primary objective of caching is to increase data retrieval performance by reducing the need to access the underlying slower storage layer.

Data StorageCaching involves temporarily storing frequently accessed data in a cache, which is a high-speed data storage layer. When a request is made, the system first checks the cache to see if the data is available.
Speeding Up Data AccessIf the data is found in the cache (a cache hit), it can be served much faster than if it had to be retrieved from the primary data storage (a cache miss), which is usually slower.
Types of CachesCaches can be implemented at browser caching, application-level caching, database caching, and CDN caching. Each serves different purposes and operates at different layers in the system architecture
How Caching Works

Challenges in Caching

  • Data Consistency. Ensuring consistency between the cache and the underlying data store can be challenging, especially in distributed systems.
  • Complexity. Implementing and managing a caching strategy adds complexity to the system. It requires careful consideration of what data to cache, when to update or invalidate the cache, and how to synchronize the cache across multiple instances in distributed systems.

Domain Name System (DNS)

DNS functions as the protocol responsible for translating human-readable domain names into IP addresses, a fundamental process that allows computers to locate and communicate with each other across the network. 

DNS is structured hierarchically. At the top of this hierarchy are the root servers, followed by the Top-Level Domains (TLDs) like .com or .net. Beneath these, we find the second-level domains, which are typically what we recognize as website names. This hierarchical design ensures an organized and efficient system for managing the vast number of domain names on the internet.

Specialized servers, known as DNS servers, handle the critical task of translating domain names into IP addresses. Whenever a user types a domain name into their browser, it’s the DNS server’s responsibility to locate the corresponding IP address. This process involves a sequence of queries starting from the DNS client on the user’s computer, progressing through various levels of DNS servers, beginning from the root level and moving downwards through the hierarchy.

Content Delivery Network (CDN)

A Content Delivery Network (CDN) is a system of distributed servers that work together to provide fast delivery of internet content. It allows for the quick transfer of assets needed for loading Internet content including HTML pages, javascript files, stylesheets, images, and videos. The primary goal of a CDN is to improve web performance by reducing the distance between the server and the user.

How CDNs Work

CDNs store a cached version of its content in multiple geographical locations, known as “points of presence” (PoPs). These PoPs contain several caching servers responsible for delivering content to visitors in their proximity. When a user requests a webpage that is part of a CDN, the CDN redirects the request from the originating site’s server to a server in the CDN that is closest to the user, thereby speeding up the content delivery.

Challenges with CDNs

  • Cache Invalidation. Ensuring that the content across all CDN servers is up-to-date can be challenging, especially when the original content changes frequently.
  • Content Management. For websites with highly dynamic content, managing and configuring the CDN to ensure the right content is cached can be complex.


Microservices architecture is an approach to software development where an application is structured as a collection of loosely coupled services. Unlike traditional monolithic architecture where all components of an application are intertwined and deployed as a single unit, microservices are small, independent, and modular. Each microservice focuses on a specific business function and can be developed, deployed, and maintained independently.

ModularityApplications are broken down into smaller, manageable pieces (services), each responsible for a specific function or feature.
IndependenceMicroservices can be deployed independently. If one service fails, it doesn’t necessarily bring down the whole application.
Technology DiversityDifferent services can be written in different programming languages and use different data storage technologies.
ScalabilityIndividual components can be scaled independently, allowing for more efficient resource use.
Continuous DeploymentEnables frequent and reliable delivery of large, complex applications.
Characteristics of Microservices

Database Replication

Database replication is a technique used in data management where the same data is stored in multiple locations to ensure consistency and high availability. This process is essential in distributed systems where data needs to be accessed and modified from different geographical locations or different system nodes.

Key Features of Database Replication

  • Data Redundancy and Reliability. Replication provides multiple copies of data, which increases its availability and reliability. In case one database server fails, other replicas can continue to serve user requests.
  • Improved Performance. Having multiple copies of data allows queries to be distributed among different servers, thereby reducing the load on a single server and improving overall system performance.
  • Backup. Replication serves as a real-time backup solution. In case of data corruption or loss in one server, the data can be recovered from another replica.
  • Data Consistency. Ensures that all copies of the database are consistent with each other. This is crucial for maintaining the integrity of the data across the system.

Common System Design Interview Questions

  • How would you design a highly available and fault-tolerant web application architecture?
  • Explain the principles of microservices architecture and when it is suitable for an application.
  • Design a URL shortening service like Bitly, discussing scalability and data storage.
  • Describe the architecture of a content delivery network (CDN) and its benefits for web applications.
  • How would you design a distributed cache system to improve application performance?
  • Discuss the design considerations for building a real-time chat application capable of handling millions of users.
    Design a recommendation system for an e-commerce platform, considering personalization and scalability.
  • Explain the architecture of a distributed file storage system like Hadoop HDFS.
  • How would you design a secure authentication and authorization system for a web application?
  • Discuss the components and considerations for building a message queuing system for asynchronous communication between services.
  • Design a scalable and fault-tolerant database system for a high-traffic application.
  • Explain the principles of load balancing and the different load balancing algorithms.
  • Describe the architecture of a logging and monitoring system for tracking application performance.
  • Design a data pipeline for processing and analyzing large volumes of data efficiently.
  • How would you create a global load-balancing system to distribute traffic across multiple data centers?

Ready to ace your next System Design Data Engineering interview? Gain the practical skills and in-depth knowledge needed to excel in interviews. With expert guidance and real-world scenarios, you’ll be well-prepared to tackle any system design interview challenge. Don’t miss out on this opportunity to level up your career in data engineering

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Throughout this article, we have delved into system design concepts and presented a diverse set of interview questions. From designing scalable web applications to architecting distributed storage systems, these questions are designed to challenge candidates and gauge their problem-solving abilities.