Top 20 System Design Interview Questions in 2026

While SDI questions tend to evolve, many have remained popular over time. These questions are well-suited to evaluate candidates on two important levels:

• Test the candidate’s understanding of System Design fundamentals.

• Evaluate the candidate’s ability to apply those fundamentals in real-world applications.

We’ll break down the top 20 System Design interview questions. These are essential questions asked at top companies such as Google, Amazon, Meta, and others. Mastering these problems and their solutions will give you a significant advantage in your System Design interview prep.

To help meet you at your current preparation level, we have divided these essential System Design problems into three difficulty levels:

Easy System Design interview questions

1. Design an API rate limiter for sites like Firebase or GitHub

2. Design a pub/sub system like Kafka

3. Design a URL-shortening service like TinyURL or bit.ly

4. Design a scalable content delivery network (CDN)

5. Design a web crawler

6. Design a distributed cache

Before we start breaking down specific questions, we want to provide you with some high-level System Design tips that will enable you to approach any problem with confidence.

Tips for any SDI question

• Start each problem by stating what you know: List all required features of the system, common problems you expect to encounter with this sort of system, and the traffic you expect the system to handle. The listing process allows the interviewer to assess your planning skills and correct any misunderstandings before you begin the solution.

• Narrate any trade-offs: Every System Design choice matters. At each decision point, list at least one positive and one negative effect of that choice.

• Ask your interviewer to clarify: Most System Design questions are purposefully vague. Ask clarifying questions to demonstrate to the interviewer how you understand the question and your knowledge of the system’s needs. Also, be sure to state your assumptions before diving into the components.

• Know your architectures: Most modern services are built upon a flexible microservice architecture. Unlike the monolithic architectures of the past, microservices enable smaller, agile teams to build independently within the larger system. Some older companies may have legacy systems, but microservices can coexist in parallel with legacy code and help refresh the company’s architecture.

• Discuss emerging technologies: Conclude each question with an overview of how and where the system could benefit from generative AI (GenAI) and machine learning (ML). This will demonstrate that you’re prepared for not only current solutions but also future solutions.

System Design interview cheat sheet

As an added bonus, we highly recommend downloading this interview cheat sheet and internalizing its contents. (Pro tip: You may even want to set it as the background for your desktop!)

Now, let’s examine the specifics of the top System Design interview questions, starting with the easy problems.

Easy System Design interview questions

We will provide a problem statement, requirements, and workflow for each question with a high-level design.

1. Design an API rate limiter for sites like Firebase or GitHub

Problem statement: Design an API rate limiter that caps the number of API calls the service can receive in a given period to avoid an overload.

Requirements

Follow these requirements for a rate limiter system:

System Design and workflow

According to the following high-level rate limiter, the client’s requests are passed through an ID builder, which assigns unique IDs to the incoming requests. The ID could be a remote IP address, login ID, or other attributes. The decision maker retrieves the throttling rules from the database and makes a decision based on them. It either forwards the requests to application servers via the request processor or discards them and provides the client an error message (429 Too many requests). If some requests are throttled due to a system overload, the system keeps those requests in a queue to be processed later.

Note: Look at the detailed design of the rate limiter to find the answers to the questions above.

2. Design a pub/sub system like Kafka

Problem statement: Design a scalable and distributed pub/sub system like Kafka that can handle massive message throughput. It should also ensure reliable message delivery and support various messaging semantics (at most once, at least once, exactly once).

Requirements

Follow these requirements for the pub/sub design:

System Design and workflow

The brokers are responsible for storing messages sent from producers and allowing consumers to read them. Similarly, the cluster manager is responsible for monitoring the broker’s health and spinning up another broker in the event that one goes down. The consumer’s details include subscription information, retention period, and other relevant details. The consumer manager manages consumers, who in turn manage consumers’ access to messages within existing topics.

Note: To answer the above technical questions, you can examine the detailed design of pub/sub.

3. Design a URL-shortening service like TinyURL or bit.ly

Problem statement: Design a scalable and distributed system that shortens long URLs like TinyURL or bit.ly. The system takes a long URL and generates a new, unique short URL. It should also take a shortened URL and return the original full-length URL.

Requirements

Follow these requirements for the URL-shortening system:

System Design and workflow

A load balancer is the first intermediary between the clients and the server, ensuring even distribution of incoming requests to maintain availability and reliability. When a new URL-shortening request comes in, the load balancer forwards it to a server where the rate limiter checks if the client is within the allowed request rate.

The server utilizes a sequencer to generate a unique numeric ID for each URL request. This ID is passed to an encoder, which converts it into a more readable alphanumeric string. The original URL and its corresponding shortened version are stored in a database. To enhance performance, recently accessed URLs are kept in a cache, allowing quick retrieval without repeatedly querying the database.

Note: To explore in depth to get the answer to the above questions, check out the detailed chapters on the TinyURL System Design.

4. Design a scalable content delivery network (CDN)

Problem statement: Design a scalable content delivery network (CDN) system to efficiently distribute and cache content across globally distributed servers, minimizing latency and ensuring reliable end-user content delivery.

Requirements

Follow these requirements for a CDN system:

System Design and workflow

When a client requests content, a request routing system kicks in to find the address of the nearest or fastest server, ensuring minimal wait time. A load balancer then routes the request to the optimal server. If the requested content is cached on that server, it is immediately delivered to the client. If not, the server fetches the content from the origin server, caches it locally for more such requests, and then serves it to the user.

The CDN system ensures that frequently accessed content remains readily available while less popular content is periodically purged. The system also includes monitoring and analytics to track performance, optimize routing, and ensure high availability and reliability.

Note: Check out the chapter on the design of a content delivery network to help you understand and get answers to the above questions.

5. Design a web crawler

Problem statement: Design a web crawler that systematically browses the internet to discover and index web pages. The crawler should efficiently navigate websites, retrieve content, and follow links to discover new pages.

Requirements

Follow these requirements for the web crawler system:

System Design and workflow

A web crawler begins by assigning a worker to a URL. Once the DNS is resolved, the worker sends the URL and IP address to an HTML fetcher to establish the connection. The URL and HTML content are extracted from the page and stored in the cache for processing. The duplicate eliminator service then tests this content to ensure no duplicate content is transferred to blob storage. Once this cycle is complete for a single URL, it moves on to the next address in the queue.

Note: To get the answers to the above questions, check out the detailed chapters on the web crawler System Design.

6. Design a distributed cache

Problem statement: Design a distributed caching system that provides fast, scalable, and reliable data retrieval across multiple servers. The system should efficiently manage cache consistency, handle high volumes of read and write requests, ensure data availability, and provide mechanisms for cache eviction and expiration.

Requirements

Follow these requirements for the distributed cache system:

System Design and workflow

A distributed caching system begins by partitioning the data across multiple cache nodes to balance the load and improve access speed. When a client requests data, an application server determines the appropriate cache node based on a consistent hashing algorithm, ensuring an even distribution of requests and quick lookups.

If the data is found in the cache (a cache hit), it is returned to the client immediately, significantly reducing latency. If the data is not found (a cache miss), the system retrieves it from the primary data store, caches it, and then serves it to the client. Cache eviction policies, such as least recently used (LRU) or time-to-live (TTL), manage the removal of stale data to free up space.

Note: To answer such conceptual questions, check out the detailed design of the distributed cache.

Medium System Design interview questions

We will provide the problem statement, requirements, workflow, and system architecture for each medium system design question.

7. Design a chat service like Facebook Messenger or WhatsApp

Problem statement: Design a scalable, reliable, and secure real-time chat service like Facebook Messenger or WhatsApp to support instant messaging, group chats, notifications, and multimedia sharing.

Requirements

Follow these requirements for the WhatsApp System Design:

System Design and workflow

In a real-time communication system, senders and receivers are connected to chat servers. Chat servers deliver messages from sender to receiver via a messaging queue. Various protocols, such as WebSocket, XMPP, MQTT, and real-time transport protocol, can be utilized for real-time communication. For this purpose, a manager establishes real-time connections between clients and chat servers; for instance, assume the WebSocket manager establishes WebSocket connections between users and different chat servers. Similarly, the messages can be persistently stored in the database.

Note: Look at the detailed design of the real-time chat service to get answers to such questions.

8. Design a mass social media service like Facebook or Instagram

Problem statement: Design a social media service used by several million users like Instagram. Users should be able to view a newsfeed with posts by following users and suggesting new content that the user may like.

Requirements

Follow these requirements for the Instagram system:

Based on the above requirements, let’s create a high-level design of a feed-based social system like Instagram.

System Design and workflow

The high-level design of a feed-based social network encompasses posts, timeline generation, a feed publishing service, and a feed ranking and recommendation engine. The post-service handles the clients’ posts, and the post is published on the client’s wall (page). Similarly, the timeline generation service generates feeds for friends and followers. The timeline generation service utilizes the feed ranking and recommendation engine, which ranks and recommends the top N posts to followers based on their interests, searches, and watch history. The generated feed is stored in the database, and the feed publishing service is responsible for publishing and showing the generated feeds to followers. As the feed could contain videos, the CDN is responsible for delivering the videos to followers with low latency.

Note: Look at the detailed design of Instagram for a better understanding.

9. Design a proximity service like Yelp or nearby places/friends

Problem statement: Design a proximity server that stores and reports the distance to places like restaurants. Users can search nearby places by distance or popularity. The database must store data for hundreds of millions of businesses across the globe.

Requirements

Follow these requirements for a System Design like Yelp:

System Design and workflow

The system handles search requests by using load balancers to distribute read requests to the read service, which then queries the quadtree service to identify relevant places within a specified radius. The quadtree service also refines the result before being sent to the clients. For adding places or feedback, write requests are similarly routed through load balancers to the writing service, which updates a relational database and stores images in blob storage. The system also involves segmenting the world map into smaller parts, storing places in a key-value store, and periodically updating these segments to include new places, although this update happens monthly due to the low probability of new additions.

Note:  Look at the detailed design of Yelp to get answers to the above questions.

10. Design a search engine-related service like Typeahead

Problem statement: Design a typeahead suggestion system that provides real-time, relevant autocomplete and autocorrect suggestions as users type, ensuring low latency and scalability to efficiently handle a large volume of queries.

Requirements

Follow these requirements for the system:

System Design and workflow

When a user starts typing a query, each character is sent to an application server. A suggestion service gathers the top N suggestions from a distributed cache, or Redis, and returns the list to the user. An alternate service, the data collector and aggregator, takes the query, analytically ranks it, and stores it in a NoSQL database. The trie builder is a service that takes the aggregated data from the NoSQL database, builds tries, and stores them in the trie database.

Note: Look at the detailed design of the Typeahead system for a better understanding of the system.

11. Design a video streaming service like YouTube or Netflix

Problem statement: Design a video streaming service like YouTube or Netflix that allows users to upload and stream videos. The service should efficiently store many videos and their metadata and return accurate and quick results for user search queries.

Requirements

Follow these requirements for a streaming service System Design:

System Design and workflow

A load balancer first handles video upload requests by sending them to the application servers. The applications server interacts with the video service, which triggers transcoders to convert the video to different formats. These typically range from 140p to 1440p but can reach 4K resolutions. The formatted video is then saved to the blob store, and its metadata is stored on the metadata database. The video service sends the transformed video to CDNs for quick content delivery to end users. Popular and recent uploads are held in a CDN. A content delivery network, or CDN, reduces latency when delivering video to users. The CDN stores and delivers requested data to users in conjunction with colocation sites.

Note: Check out the detailed chapter on YouTube System Design that answers the above concerns during the design.

12. Design a ride-sharing service like Uber or Lyft

Problem statement: Design a system for a ride-sharing service similar to Uber, where users can request rides and drivers can accept these requests. The system should efficiently match drivers with riders based on location and availability, handle real-time updates on ride statuses, manage payments securely, and ensure a seamless user experience from booking to ride completion.

Requirements

Follow these requirements for the System Design:

System Design and workflow

A user’s request is sent to the application server via a load balancer and API gateway. The system accepts the rider’s request, and the trip service or manager provides an estimated time of arrival (ETA) based on the type of vehicle. The drivers and location manager use a matching algorithm to find the nearest available drivers and send the request to those drivers by notifying them via a notification service. When a driver matches with a rider, the application should return the trip and rider information. The driver’s location is regularly recorded and communicated to relevant users through a pub/sub service.

Once the ride is complete, the trip manager ensures payment is securely processed through a payment gateway. We leverage a database that stores user and driver profiles, ride history, and payment information. We also utilize caching mechanisms to expedite access to frequently requested data, and continuous monitoring ensures the service operates smoothly.

Note: Check out the detailed chapter on Designing Uber that answers the above concerns during the design.

13. Design a social network service like Reddit or Quora

Problem statement: These social network sites operate on a forum-based system that allows users to post questions and links. For simplicity’s sake, focus more on designing Quora. You’ll unlikely need to walk through the design of something like Reddit’s subreddit or karma system in an interview.

Requirements

Follow these requirements for a System Design like Quora:

System Design and workflow

In Quora’s high-level design, users interact through a web server, which communicates with an application server to handle actions such as posting questions, answers, and comments. Content, such as images and videos, is stored in blob storage, while question-and-answer data, along with user profiles and interactions, are stored in a MySQL database.

A machine learning engine analyzes user interactions and content to rank answers based on relevance and quality. This engine continuously learns from user feedback to improve its ranking algorithms. For personalized user experiences, a recommendation system utilizes machine learning models to tailor content based on individual interests and behaviors.

Note: Check out the detailed chapter on Quora System Design to help you understand the system.

Hard System Design interview questions

Hard System Design interview questions pertain to complex, open-ended problems that necessitate in-depth technical knowledge, critical thinking, and the ability to design scalable and efficient systems within constraints. Let’s start with the System Design of a ChatGPT-style service.

14. Design a text-to-text generation system like ChatGPT

Problem statement: Design a scalable text generation system that can handle real-time, context-aware conversations. The system must accept user prompts, generate human-like responses, maintain conversation context, and support personalization, while ensuring low latency, high availability, and secure handling of user data.

Requirements

Follow these requirements for the ChatGPT-style service:

System Design and workflow

When a user submits a prompt, the API Gateway handles authentication and rate limiting, and a load balancer distributes the request to application servers. The input is pre-processed by the NLU service, which extracts intent, entities, and embeddings to maintain context. Model servers generate responses using conversation history. Responses pass through content moderation, while user feedback is collected to improve the system. Finally, the response is returned to the user, enabling a fast, context-aware conversation.

The following illustrations show a high-level design of a ChatGPT-style service:

15. Design a code deployment system

Problem statement: Design a reliable and scalable code deployment system for a large-scale distributed application. The system should automate the building, testing, and deployment of code changes across environments with minimal disruption, while also providing the ability to monitor and roll back changes as needed.

Requirements

Follow these requirements for a code deployment system:

System Design and workflow

The high-level design of the code deployment system includes all the major components needed to meet the outlined requirements. The process begins when developers submit code to a version control system (VCS). Any new code changes trigger a continuous integration (CI) service, which automatically integrates updates, runs preliminary tests, and prepares the code for deployment. Once validated, the code is published to a queue, which decouples build triggers from execution.

A dedicated build service listens to this queue and retrieves jobs to compile the code. It then generates binary artifacts and stores them in a versioned blob storage system. These artifacts represent the system’s deployable output. When it’s time to deploy, the deployment service pulls the necessary artifacts from blob storage and installs them on machines across different regions. This ensures consistent deployments across multiple environments, including staging and production.

The architecture supports gradual rollouts, rollback mechanisms, and monitoring at each step, helping to reduce risks and improve reliability in production.

A high-level design of a code deployment system is depicted in the following illustration:

Note: Look at the Design a Deployment System for a better understanding of the system.

16. Design a social media newsfeed service

Problem statement: Design a scalable and efficient social media newsfeed system that delivers personalized, real-time content updates to users, ensuring low latency, high availability, and scalability.

Requirements

Follow these requirements for the design:

System Design and workflow

In the following high-level design of a newsfeed system, clients post or request their newsfeed through the app, which the load balancer redirects to a web server for authentication and routing. Whenever a post is created via the post service and available from a user’s friends (or followers), the notification service informs the newsfeed generation service, which generates newsfeeds from the posts of the user’s friends (followers) and keeps them in the newsfeed cache. Similarly, the generated feeds are published by the newsfeed publishing service to the user’s timeline from the news feed cache. It also appends multimedia content from the blob storage with a news feed if required.

Note: If you need answers to such questions, look at the detailed design of a newsfeed service.

17. Design a collaborative editing service like Google Docs

Problem statement: Design a collaborative editing service that lets users remotely and simultaneously make changes to text documents. The changes should be displayed in real time. Like other cloud-based services, documents should be consistently available to any logged-in user on any machine. Your solution must be scalable to support thousands of concurrent users.

Requirements

Follow these requirements for the Google Docs system:

System Design and workflow

Clients’ requests are forwarded to the operations queue, where conflicts are resolved between different collaborators, and the data is stored in the time series database and blob storage (responsible for storing media files). Autocomplete suggestions are made via the typeahead service. This service resides on the Redis cache to enable low-latency suggestions and enhance the speed of the regular updates process. The application servers perform several important tasks, including importing and exporting documents. Application servers also convert documents from one format to another. For example, a .doc or .docx document can be converted into .pdf or vice versa.

Note: If you need answers to such questions, look at the detailed design of Google Docs.

18. Design Google Maps

Problem statement: Design a service that can map the route between two locations. The system should map several optimal paths to a destination based on the mode of travel. Each route should display the total mileage and an estimated time of arrival.

Requirements

Follow these requirements for the Google Maps system:

System Design and workflow

In the Google Maps system, clients request location-based services, such as finding a route or searching for nearby points of interest. The load balancer directs requests to various services based on the nature of the query.
For routing requests, the route finder service calculates the optimal paths between two or more points, utilizing both real-time and historical data. It relies on the graph processing service to perform complex calculations on the road network graph stored in the graph database. The location finder service provides the user’s current location or identifies the location of a specified point of interest. The area search system enables users to locate nearby places, such as restaurants or gas stations, by querying the graph database and third-party road data sources.

Note: Look at the detailed design of Google Maps to get answers to the questions above.

19. Design a payment gateway like Stripe

Problem statement: Design a payment gateway like Stripe capable of securely performing online or card transactions and handling millions of users simultaneously.

Requirements

Follow these requirements for the system:

System Design and workflow

Initially, a customer selects a product or service via the merchant’s online store and proceeds to the checkout page to provide payment details, including card number, cardholder name, CVV or CVC, and expiration date. Upon clicking the pay button, an event that hits the payment service stores the event, performs initial security checks, and forwards the payment details to the payment service provider for further operations is generated. The payment gateway performs extensive security checks, transfers money from the customer’s account to the merchant’s, and provides additional services such as handling refunds and generating invoices. The card network verifies the card information via APIs provided by the card network. Once the payment is processed, the wallet and ledger service updates the merchant’s wallet in the database to track total revenue and processes each order separately in case of multiple sellers. The reconciliation system matches and verifies financial records to ensure accurate transaction accounting, identifying and resolving discrepancies.

Note: Look at the Design a Payment System for a better understanding of the system.

 20. Design a Scalable Data Platform for ML/AI Systems

Problem statement: Design a scalable data infrastructure that supports the machine learning lifecycle. The system must ingest data from diverse sources, process and transform it into high-quality features, and serve these features to models for both historical training and low-latency real-time inference, while ensuring consistency between the two.

Requirements 

Follow these requirements for the ML Data Platform:

System Design and workflow 

In a large-scale data infrastructure, data enters the platform through a data ingestion layer that supports dual paths: the message queue buffers real-time events processed by the stream processing engine, while batch loads are orchestrated by a workflow orchestrator.

From there, the data processing layer transforms raw data into clean features. Crucially, this layer acts as a “dual-publisher,” writing the same computed features to two destinations in the feature store layer: an offline store for generating historical training sets, and an online store (Redis/key-value store) for serving the latest values to live models. This architecture ensures that the logic used for training is mathematically identical to that used for inference, solving the “training-serving skew” problem.

Note: To explore in depth and get the answers to the above questions, check out the detailed chapter on the Design of a Scalable Data Infrastructure for AI/ML.

Bonus Design problems

In addition to the above System Design interview questions, here are a couple of more design problems that would help you excel in your System Design interview.

1. Design a food delivery service like Uber Eats or DoorDash

Problem statement: Design a food delivery service like Uber Eats or DoorDash that efficiently connects hungry customers with diverse restaurants, ensuring timely and accurate order fulfillment while optimizing delivery routes and driver earnings.

Requirements

Follow these requirements for the DoorDash system:

System Design and workflow

The following is a level design of DoorDash, which consists of several services serving different purposes. Let’s describe the workflow and the interaction of the different services involved in the design.

Customers’ requests are routed through the API gateway and directed to different services via the load balancer. The search service searches for menu items, cuisines, restaurants, etc. It is one of the customers’ busiest services when searching for information on the website or application. The ordering service handles menu selection, managing the shopping cart, and placing food orders. Additionally, it facilitates payment processing through an external payment gateway and stores the outcomes in the relevant database. The order fulfillment service is used to manage the orders that the restaurants have accepted. It also keeps track of orders being prepared.

Customers and restaurant staff use the user management service to create and manage their profiles. The dispatch service displays the orders ready to be picked. It is also used to view delivery information and facilitate communication between customers and restaurant staff.

2. Design a video-first social platform like TikTok

Problem statement: Design a video-first social platform where users can create, upload, watch, and interact with short-form videos (reels). The system should support millions of users, deliver low-latency content, and personalize each user’s video feed based on engagement history.

Requirements

Follow these requirements for a video-first social platform:

System Design and workflow

When users open the app, their request is routed to the feed generation service through a load balancer. This service works with a recommendation service to generate a personalized list of videos based on the user’s watch history, likes, and other interactions.

Once the feed is generated, the app streams video content directly from a content delivery network (CDN) to ensure fast loading times, especially for users in different parts of the world. The videos are stored in a media storage system and processed by a video processing service, which handles compression, format conversion, thumbnail generation, and basic moderation.

When a user uploads a video, it’s routed to the video processing service. After processing, the video is saved to media storage, which can be included in the personalized list for users through the recommendation service.

The following high-level design represents a simple workflow of a video-first social platform like TikTok:

Conclusion

Mastering these 20 System Design questions will equip you with the foundational knowledge and practical skills needed to excel in technical interviews at top companies. Remember that System Design is about understanding trade-offs, asking clarifying questions, and demonstrating your ability to think systematically about complex problems. Practice these questions regularly, focus on articulating your design decisions clearly, and you’ll build the confidence to tackle any System Design challenge that comes your way.