Top 30+ System Design Interview Questions and Answers

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System design is the process of defining the architecture and components of a software system. It helps teams plan how a system will work, scale, and handle data. The idea of structured system design goes back to the 1960s when engineers started creating large computer systems. It evolved over time as software grew more complex. Today, companies use system design to build everything from social media apps to payment systems. If you are preparing for tech roles, understanding system design interview questions is a must. Let’s look at the most commonly asked ones.

Fun Fact – System design interviews are intentionally open-ended – interviewers often adapt their questions in real time based on how you think, not what you build.

System Design Interview Questions for Freshers 

Here are some important interview questions system design topics that freshers should prepare for before entering tech interviews.

1. What is system design?

System design is the process of planning how software systems will work. It includes defining architecture, data flow, modules, and how components connect. The goal is to build scalable, reliable, and maintainable systems.

2. What is the CAP theorem? How does it influence database choice?

CAP theorem says a distributed system can’t guarantee Consistency, Availability, and Partition Tolerance all at once. In the presence of network partitioning, a distributed system can only guarantee either consistency or availability – not both.

For example, if your app needs high availability and can tolerate delayed consistency, you might pick Cassandra over a strongly consistent database.

3. What are the differences between horizontal and vertical scaling?

Horizontal scaling means adding more machines to handle traffic.

Vertical scaling means upgrading a single machine’s CPU, RAM, or storage. 

Horizontal scaling is preferred in distributed systems because it avoids single points of failure.

4. How would you design a cache strategy like cache-aside, write-through, or write-behind?

In cache-aside, the app reads from the cache first, then DB if missing. Write-through updates both cache and DB on every write. Write-behind writes to cache immediately, then DB later. I would choose based on how fresh the data needs to be and traffic type.

5. What is load balancing and what components are involved?

Load balancing distributes traffic across multiple servers to prevent overload. It uses health checks, routing algorithms (like round robin or least connections), and works with reverse proxies like NGINX or HAProxy.

6. Describe latency, throughput, and availability and how to optimise them.

Latency is response time. 

Throughput is how much work a system can do. 

Availability is the percentage of time a system works. 

I would reduce latency using caching and faster queries, improve throughput with parallelism, and keep availability high using failover systems.

7. How would you shard a database and when is it necessary?

Sharding splits data across multiple machines using a shard key. It is useful when one machine can’t handle read/write load or data size. Choosing the right key avoids hotspots and keeps performance stable.

8. Explain the difference between SQL and NoSQL databases.

Aspect	SQL Database	NoSQL Database
Data Model	Relational (tables with rows and columns)	Non-relational (documents, key-value, graph, etc.)
Schema	Fixed and predefined	Dynamic and flexible
Best For	Complex queries and relationships	High-speed operations and scalable applications
Examples	MySQL, PostgreSQL, Oracle	MongoDB, Redis, Cassandra

Also Read - Top 35+ MongoDB Interview Questions and Answers

System Design Interview Questions for Experienced 

These interview questions system design topics are often asked in interviews for experienced professionals and senior tech roles.

9. How would you design a real-time location tracking system (like ride-hailing apps)?

Objective: Track live location of drivers and update rider UI.

Key Features:

• Location updates every 2–5 seconds
• Nearby driver visibility
• ETA calculation

Challenges:

• High frequency GPS updates
• Offline drivers or sudden disconnects

Approach: Use GPS data sent via mobile SDK. Kafka streams location events. Redis stores latest coordinates. A pub-sub system (like Google Pub/Sub) notifies matching systems. Stale sessions are expired after a timeout.

10. How would you design a global file storage system like Google Drive?

Objective: Store and sync files across users and devices.

Key Features:

• File uploads/downloads
• Version control
• Sharing and permissions

Challenges:

• Handling large file sizes
• Device conflicts

Approach: Split files into chunks. Store in S3 or similar object storage. Maintain metadata (file name, owner, chunk map) in a DB. Use file hashes for deduplication. Sync tokens help detect changes. CDNs speed up access.

11. Explain how you would build a rate limiter for distributed APIs.

Objective: Restrict number of API calls per user/IP.

Key Features:

• Per-user or per-API limits
• Millisecond-level accuracy
• Distributed consistency

Challenges:

• Multiple servers need shared state
• Handling burst traffic

Approach: Use token bucket or sliding window algorithm. Store counters in Redis. Sync across services via Redis Cluster or sharded cache. Return 429 Too Many Requests with retry-after headers.

12. How would you design a push notification service at large scale?

Objective: Deliver notifications to users in near real-time.

Key Features:

• FCM/APNs integration
• Retry and batch support
• User preferences

Challenges:

• Token expiry and failures
• Volume spikes

Approach: Queue messages with Kafka. Workers send using FCM/APNs. Batch similar messages. Store preferences in a DB. Use exponential backoff on retries. Remove expired tokens periodically.

13. Describe your design for a live video streaming service (e.g., Netflix).

Objective: Stream high-quality video to users with minimal buffering.

Key Features:

• Adaptive bitrate streaming
• Global CDN delivery
• Real-time playback tracking

Challenges:

• High bandwidth usage
• Multi-device compatibility

Approach: Ingest servers process live streams. Transcode into HLS/DASH formats. Store on cloud storage/CDNs. Players request chunks based on bandwidth. Analytics system logs view stats and buffering issues.

Low Level Design Interview Questions

This section covers important LLD interview questions that test your understanding of object-oriented principles, class design, and system components.

14. Design classes for a parking lot management system.

Objective: Manage entry, parking, and exit of vehicles.

Key Classes:

• ParkingLot (has multiple Levels)
• Level (contains multiple ParkingSpots)
• ParkingSpot (tracks spot ID, vehicle type, and availability)
• Vehicle (base class with type, plate number)
• Ticket (stores entry time, assigned spot, fee details)

Relationships:

• A Vehicle occupies a ParkingSpot.
• ParkingLot uses TicketService to generate and close tickets.

Design Tip: Use inheritance for Car, Bike, Truck from Vehicle.

15. How would you design the core objects and relationships for a tic-tac-toe game?

Objective: Model gameplay, players, and win conditions.

Key Classes:

• Game (controls flow, checks game state)
• Board (contains a 3×3 grid of Cells)
• Player (has ID, symbol like X or O)
• Move (stores player and cell coordinates)

Design Tip: Use GameState enum (IN_PROGRESS, DRAW, WIN) to track status.

Bonus: Add AIPlayer for single-player mode.

16. Create object-oriented models for an API rate limiter

Objective: Control API request volume per user/IP.

Key Classes:

• RateLimiter (entry point for checking limits)
• UserBucket (stores allowed requests and refill time)
• Token or Permit (optional object to signal request grant)

Logic:

• Sliding window or token bucket logic is implemented in UserBucket.
• RateLimiter maps users to their respective UserBucket.

Design Tip: Keep time-based logic inside each bucket for encapsulation.

High Level Design Interview Questions

This section includes key HLD interview questions that focus on system architecture, scalability, and component interaction at a broader level.

17. Design the architecture for a URL shortening service.

Goal: Accept long URLs and return short, unique aliases.

Components:

• REST API (to create/resolve links)
• ID generator (base62 encoding, hash, or counter)
• Key-Value Store (Redis or SQL for mapping short → long)
• TTL logic for expiring links
• Analytics module (tracks clicks and usage)

Scalability Tips: Use load balancers, cache popular short URLs, and store metadata asynchronously.

18. Outline high-level design for a distributed web crawler

Goal: Crawl the web for data and index it efficiently.

Components:

• URL Frontier Queue (stores URLs to visit)
• Scheduler (prioritizes domains, checks robots.txt)
• Worker Nodes (fetch and parse content)
• Deduplication Layer (removes repeated URLs)
• Parser & Extractor (gets links, metadata, content)
• Storage Layer (search index like Elasticsearch or raw DB)

Challenges: Avoid overloading domains, avoid crawling spam, respect crawl policies.

19. Describe the HLD for a social news feed system (Quora or Reddit)

Goal: Show users posts based on their interests.

Components:

• Follow Graph (users, tags, topics)
• Feed Generator (collects relevant posts)
• Ranking Engine (uses recency, upvotes, user activity)
• Feed Cache (per-user timeline, refreshed periodically)
• Notification System (informs on new posts/comments)

Scalability: Use queues for async fanout. Partition users by region or activity level.

Also Read - Top 50+ REST API Interview Questions and Answers

Front End System Design Interview Questions

Here are front end system design interview questions that test your knowledge of UI architecture, performance, and user experience at scale.

20. How would you design a scalable UI architecture for a dashboard app?

A scalable UI should follow a modular structure. Shared layout components like headers and navigation are separated from business-specific features. Each feature is packaged as a standalone module, allowing independent development and deployment. A design system manages reusable UI elements. Lazy loading is used to load modules on demand, reducing the initial bundle size and improving performance.

21. How do you handle front-end caching and state management in large SPAs?

For persistent caching, localStorage or IndexedDB can store non-sensitive data. App-wide state is managed with Redux Toolkit or Zustand, while server state is handled by React Query or SWR. Expensive operations are memoized, and re-renders are minimized by isolating local state within components where possible. This approach balances performance with maintainability in large single-page applications.

22. Design the front-end interaction flow for a real-time chat application.

The app initiates a WebSocket connection when a user logs in. Outgoing messages are sent through the socket and rendered using optimistic updates. Incoming messages are pushed from the server and appended to the chat UI in real-time. If the user is offline, messages are queued with a “sending” status and synced automatically upon reconnection. Missed messages are fetched on reconnect to keep the chat history complete.

System Design Interview Questions Asked at the Top IT Companies

Let’s go through some real system design interview questions commonly asked at companies like Google, Amazon, and Microsoft.

Google System Design Interview Questions

1. How would you design a global file syncing system like Drive?
2. Describe the architecture of Google Photos including thumbnail generation and search.
3. How would you scale the Google Search crawler?
4. Design a traffic control system for smart cities.
5. How would you build a type-ahead search service for billions of queries?

Amazon System Design Interview Questions

Here are the common Amazon system design questions that test your ability to build scalable and reliable systems.

1. How would you design a driver delivery assignment system for Amazon Flex or Last Mile delivery?
2. Design a CDN for global content delivery across AWS regions.
3. How would you build a scalable checkout and cart service?
4. Design a high-throughput notification system for order status updates.
5. How would you design a self-service cache invalidation system for product pages?

Microsoft System Design Interview Questions

Here are Microsoft system design questions that often focus on scalability and integration with Azure services.

1. How to architect OneDrive for large file sync across platforms?
2. Design an HLD for Microsoft Teams chat and video system.
3. How would you build a scalable telemetry logging service (like Windows Update telemetry)?
4. Plan the architecture for search autocomplete in Office apps.
5. Design a scalable developer authentication system using Azure AD.

Meta System Design Interview Questions

1. How would you design Facebook’s newsfeed generation system?
2. How would you build photo/video storage and content delivery at scale?
3. Architect a live comment streaming system during large live events.
4. How would you design WhatsApp’s message delivery system for unreliable mobile networks?
5. Design the Instagram stories feature – from upload to playback.

PayPal System Design Interview Questions

1. How would you design a secure online payment gateway?
2. Design a system for fraud detection in real-time transactions.
3. How would you build a ledger service for processing fund transfers?
4. Architect a queueing system for batch settlement at end of day.
5. Plan a system for multi-currency conversion and reconciliation.

Atlassian System Design Interview Questions

1. Design the back-end architecture for Jira issue tracking.
2. How would you build real-time collaborative editing in Confluence?
3. Design a scalable plugin marketplace for Atlassian tools.
4. Architect notification delivery for project updates.
5. How would you build secure SSO across their SaaS ecosystem?

Uber System Design Interview Questions

1. Design the driver-rider matching and dispatch system.
2. How would you build ETA calculation and route optimisation?
3. Architect scalable event logging for ride tracking.
4. Design surge pricing mechanisms in real time.
5. Plan a fault-tolerant trip billing system.

Agoda System Design Interview Questions

1. How would you design a global hotel booking search engine?
2. Design a cache-invalidation mechanism for dynamic pricing.
3. How would you build real-time availability syncing across partners?
4. Architect a fault-tolerant reservation system.
5. Design a hotel review aggregation service.

Walmart System Design Interview Questions

1. How would you design an online grocery ordering backend?
2. Architect inventory syncing across stores and e-commerce.
3. Design a demand forecasting system for restocking.
4. How would you build queue handling for flash sales?
5. Plan the design for delivery route optimisation.

Android System Design Interview Questions

1. How would you design inter-app communication architecture?
2. Architect a permission and authentication system on Android.
3. Design the backup and restore service in Android OS.
4. How would you build a modular front-end for Launchers?
5. Plan system update distribution for billions of devices.

Salesforce System Design Interview Questions

1. How would you design Salesforce’s multi-tenant data architecture?
2. Design the back-end for approval workflows.
3. How would you build metadata-driven schema updates?
4. Architect real-time reporting and dashboard system.
5. Plan an event-driven integration service for external systems.

Also Read - Top 30+ Salesforce Interview Questions and Answers

Goldman Sachs System Design Questions

1. Design a low-latency trading system for stock orders.
2. How would you build a market data feed ingestion and distribution?
3. Plan trade reconciliation across global markets.
4. Architect a risk-analysis system handling millions of transactions.
5. Design a fraud-detection engine for trading anomalies.

Oracle System Design Interview Questions

1. How would you design a global distributed database?
2. Architect a backup and recovery system with point-in-time restore.
3. Design a distributed transaction coordinator.
4. How would you build real-time replication across data centers?
5. Plan an optimizer for SQL query execution.

Flipkart System Design Interview Questions

1. Design the system for product search ranking and filtering.
2. How would you build a real-time order tracking system?
3. Architect the design for flash sale event handling.
4. Plan the inventory management across warehouses.
5. Design recommendation service for personalized user offers.

LinkedIn System Design Interview Questions

1. How would you design the feed algorithm for professional updates?
2. Architect connection suggestion (People You May Know).
3. Design the messaging system with offline sync.
4. How would you build skill endorsement tracking and display?
5. Plan a scalable job recommendation engine.

Visa System Design Interview Questions

1. How would you design global transaction routing and authorization?
2. Architect fraud-detection rules engine at scale.
3. Design the clearing and settlement system.
4. How would you build tokenisation for card data?
5. Plan chargeback processing pipeline.

System Design MCQs

1. Which technique involves splitting database tables for performance and availability?

A. Indexing
B. Partitioning
C. Normalization
D. Replication

Answer: B. Partitioning

2. Which caching strategy directly writes to both cache and the database on each update?

A. Cache-aside
B. Write-through
C. Write-behind
D. Read-through

Answer: B. Write-through

3. What does horizontal scaling require that vertical scaling does not?

A. Faster CPUs
B. Larger RAM
C. Load Balancer
D. Disk Mirroring

Answer: C. Load Balancer

4. Which consistency model allows reads to eventually reflect recent writes?

A. Strong Consistency
B. Eventual Consistency
C. Weak Consistency
D. Causal Consistency

Answer: B. Eventual Consistency

5. What’s the primary role of a load balancer in a distributed system?

A. Encrypt all outgoing requests
B. Backup data across regions
C. Route traffic evenly across servers
D. Detect server failures

Answer: C. Route traffic evenly across servers

6. In leader election, what problem does it solve?

A. Assigning user IDs
B. Coordinating between distributed services
C. Encrypting communication
D. Reducing query latency

Answer: B. Coordinating between distributed services

7. What is sharding and why is it used?

A. Mirroring data for backup
B. Encrypting database content
C. Dividing data into parts to distribute load
D. Normalizing data across columns

Answer: C. Dividing data into parts to distribute load

8. Which component is essential to a system handling millions of concurrent location updates?

A. Webhooks
B. Real-time Pub/Sub System
C. Email Notification System
D. Content Delivery Network

Answer: B. Real-time Pub/Sub System

9. What is a key design challenge in a global CDN?

A. Managing user passwords
B. Scaling a relational database
C. Ensuring low latency from edge locations
D. Handling keyboard input

Answer: C. Ensuring low latency from edge locations

System Design Interview Preparation Tips

Here are some tips to help you prepare for system design interview –

• Start with basics like scalability, availability, and consistency
• Practice common questions and sketch your answers on paper
• Study real-world systems like URL shorteners, chat apps, and video platforms
• Use “Grokking the System Design Interview” for structured problem breakdowns
• Read “System Design Interview – An Insider’s Guide” to learn trade-offs
• Don’t memorize – focus on approach and clarity
• Mock interviews help a lot to prepare for system design interview confidently

Wrapping Up

And there you have it – the top 30+ system design interview questions and answers to help you prepare. These questions reflect what top companies actually ask during technical rounds. For those looking for system design job opportunities, Hirist is a great platform to find IT jobs, including openings that involve system design work.

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