How to prepare for a system design interview in 2 days?

Preparing for a system design interview in just 2 days can be challenging, but with a focused approach, you can cover the essential concepts and frameworks necessary to succeed. Here’s a step-by-step plan to maximize your preparation in a short time:

Day 1: Focus on Core Concepts and Common System Design Patterns

1. Understand the Basics of System Design

Start by reviewing the fundamental concepts of system design, focusing on key areas that are frequently tested in interviews. Use the first few hours to grasp these essentials:

• Scalability: How systems scale vertically (adding more resources to a single server) and horizontally (adding more servers).
• Load Balancing: How load balancers distribute traffic across servers and ensure high availability.
• Database Design: Differences between SQL and NoSQL databases, their use cases, and when to choose one over the other.
• Caching: Learn caching strategies (e.g., write-through, write-back, cache invalidation). Understand how to use Redis or Memcached to improve performance.
• Data Partitioning (Sharding): How to distribute data across multiple servers or databases to scale horizontally.
• Consistency vs. Availability: Understand the CAP theorem and how to make trade-offs between consistency, availability, and partition tolerance in distributed systems.

2. Study Common System Design Patterns

Several system design problems appear frequently in interviews, so understanding how to approach them will give you a strong foundation:

• Design a URL Shortener: Focus on generating unique short URLs, mapping them to long URLs, and handling heavy read traffic.
• Design a Messaging System (like WhatsApp): Focus on real-time messaging, message delivery, and scaling.
• Design a Distributed Caching System: Understand how to cache frequently accessed data and how to handle cache invalidation.
• Design a News Feed System (like Facebook): Handle real-time feed updates, prioritization, and scaling to millions of users.
• Design a Video Streaming Service (like YouTube): Focus on delivering video content, using CDNs for caching, and handling concurrent users.

3. Learn to Draw High-Level Architectures

• Practice sketching high-level architecture diagrams for the common system design problems mentioned above. Use simple tools like Google Jamboard, Miro, or Excalidraw to represent key components (clients, databases, caches, load balancers, etc.).
• Keep it simple: Focus on the overall flow of data between components and how different parts of the system communicate.

Day 2: Deepen Understanding and Practice Key Problems

1. Dive Deeper into Two or Three Key Systems

Since time is limited, pick 2-3 system design problems that are most likely to appear in interviews. Study these deeply so you can explain them thoroughly during the interview.

a. Example 1: URL Shortener

• Problem: How do you take a long URL and generate a short one, ensuring it can scale to handle millions of users?
• Key Concepts: Hashing for generating short URLs, database for storing mappings, cache for frequently accessed URLs, load balancing for handling traffic.

Diagram: Draw a simple flow of how the client interacts with the system (user requests a short URL, system generates and stores it, and user retrieves the original URL through redirection).

b. Example 2: Real-Time Messaging System

• Problem: Design a system like WhatsApp or Slack that handles real-time messages between users.
• Key Concepts: Message queues, database design (conversations, messages), real-time updates, caching, handling high availability.

Diagram: Show how messages flow from a user’s device to the backend, how they are stored in a database, and how they are delivered to other users in real time.

c. Example 3: Video Streaming Platform

• Problem: Design a scalable video streaming service (e.g., YouTube or Netflix).
• Key Concepts: Content delivery networks (CDNs), video storage, transcoding for different formats, load balancing, caching popular content.

Diagram: Draw how a user accesses the video, how the system serves videos using CDNs, and how user data (likes, views) is stored.

2. Practice Explaining Designs Out Loud

• After reviewing the designs, practice explaining them out loud as if you’re in an interview. This will help you communicate your ideas clearly during the actual interview.
• Focus on the key components, data flow, and trade-offs in your designs. If possible, use a friend or family member as an audience to simulate a mock interview.

3. Understand Trade-offs and Bottlenecks

In system design interviews, you’ll often be asked about trade-offs and how your system will handle bottlenecks. Be prepared to discuss:

• Consistency vs. Availability: If you’re designing a messaging system, explain whether strong consistency is needed or if eventual consistency will work.
• Handling Traffic Spikes: For a video streaming service, explain how CDNs and load balancers help manage spikes in traffic.
• Database Sharding: For a URL shortener, explain how you’ll shard the database to handle millions of entries.

4. Handle Edge Cases

Every system has edge cases, and interviewers often ask how your design handles them. Be prepared to answer questions like:

• What happens if the cache fails? (e.g., for a news feed system)
• How does the system recover from database failure? (e.g., for a URL shortener)
• How will you handle a sudden spike in traffic? (e.g., for a messaging app during a viral event)

Extra Tips for Interview Day

1. Stay Calm and Structured

• Approach the problem methodically. Start by asking clarifying questions about requirements, traffic, and non-functional needs (e.g., availability, latency).
• Think out loud: The interviewer wants to understand your thought process, so make sure you explain why you’re choosing certain components or strategies.

2. Use Simple Diagrams

• Keep your diagrams clear and high-level. Use boxes and arrows to represent components and show how data flows between them. Don’t worry about making it perfect—focus on showing the system’s structure and interactions.

3. Be Open to Feedback

• If the interviewer suggests changes or asks for modifications, be flexible. This shows that you can adapt your design based on new information or feedback.

4. Summarize Your Design

• End by recapping your design, emphasizing how it meets the system’s requirements and addressing any trade-offs you made for scalability, performance, or availability.

Conclusion

Preparing for a system design interview in just 2 days is intense, but with focus, you can still cover essential concepts. Concentrate on mastering the core system design principles and practice explaining high-level architectures for common system design problems. The goal is to communicate your thought process clearly and demonstrate your ability to design scalable, reliable systems.

Key Focus Areas:

• Understand the basics: scalability, caching, databases, load balancing.
• Practice 2-3 common system design problems deeply.
• Draw and explain simple high-level diagrams.
• Address trade-offs and edge cases.