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Comprehensive Roadmap for Low-Level and High-Level Design Interview Preparation

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Generated using deepai.org
By Pravin Tripathi
5 min read
Comprehensive Roadmap for Low-Level and High-Level Design Interview Preparation

System design interviews are a critical part of the hiring process for software engineering roles, especially for senior positions. These interviews assess your ability to design scalable, maintainable, and efficient systems to solve real-world problems. In this blog, we’ll cover a combined roadmap for both Low-Level Design (LLD) and High-Level Design (HLD) interview preparation, along with strategies, expectations, and steps to excel in these interviews.

What is a System Design Interview?

In a system design interview, you are given a real-world problem and expected to design a system to solve it. Since no system is perfect, you must also identify trade-offs, pros, and cons of your design. The goal is to evaluate your ability to:

  1. Analyze requirements and define system constraints.
  2. Design scalable and maintainable systems.
  3. Identify trade-offs and justify your design decisions.

Whether it’s low-level or high-level design, the core focus is on your problem-solving skills, understanding of system architecture, and ability to communicate your ideas effectively.

Low-Level Design (LLD) Interviews

Low-Level Design focuses on the implementation details of a system. It involves designing class structures, defining entities, and applying design principles and patterns to create a robust and extensible system.

Expectations in LLD Interviews:

  1. Requirement Gathering: Identify and define system requirements and constraints.
  2. Entity Identification: Define entities (classes) and their relationships.
  3. Design Principles: Apply principles like SOLID to ensure good design.
  4. Design Patterns: Use patterns like Strategy, Builder, Singleton, etc., to solve common design problems.
  5. System Maintainability: Ensure your design is extensible, loosely coupled, and easy to maintain.

LLD Learning Strategy

1. Understand Core Concepts

  • Learn the fundamentals of object-oriented programming (OOP).
  • Understand design principles like SOLID, DRY, and KISS.
  • Study design patterns such as:
    • Strategy
    • Builder
    • Singleton
    • Factory
    • Command
    • Composition over Inheritance

2. Practice Problems

  • Solve real-world problems like designing a Parking Lot, Elevator System, or Library Management System.
  • Focus on identifying trade-offs and comparing your design with others.

3. Steps in an LLD Interview

  • Step 1: Define Model Classes: Identify entities and create classes for them.
  • Step 2: Define Properties: Add fields and attributes to each class.
  • Step 3: Define Behavior: Implement methods for each class. Start with top-level methods and drill down to discover additional methods as needed.

High-Level Design (HLD) Interviews

High-Level Design focuses on the architecture and scalability of a system. It involves designing services, choosing data storage solutions, and ensuring the system can handle high loads and remain fault-tolerant.

Expectations in HLD Interviews:

  1. Requirement Gathering: Define system constraints and use cases.
  2. Component Identification: Identify core components like databases, queues, caches, etc.
  3. Scalability and Availability: Design for high scalability, fault tolerance, and concurrency control.
  4. Trade-offs: Justify your design choices and discuss pros and cons.

HLD Learning Strategy

1. Learn Core Concepts

  • Study scalability techniques like partitioning, sharding, and replication.
  • Understand high availability concepts like quorums and leader election.
  • Learn about backend components:
    • Databases: SQL vs. NoSQL, database schemas, and indexing.
    • Queues: Kafka, RabbitMQ, and their use cases.
    • Caches: Redis, Memcached, and caching strategies.
    • Blob Storage: S3, Google Cloud Storage, etc.

2. Practice Problems

  • Solve problems like designing URL Shorteners, Social Media Platforms, or E-commerce Systems.
  • Focus on creating component diagrams and defining high-level flows.

3. Steps in an HLD Interview

  • Step 1: Gather Requirements: Clarify use cases, constraints, and assumptions.
  • Step 2: Create a High-Level Design: Sketch components (e.g., services, databases, caches) and their interactions.
  • Step 3: Design Core Components: Dive deep into critical components (e.g., URL hashing, database schemas).
  • Step 4: Scale the Design: Address bottlenecks using techniques like load balancing, caching, and sharding.

Combined Roadmap for LLD and HLD Preparation

1. Learn the Fundamentals

  • LLD: Focus on OOP, design principles, and patterns.
  • HLD: Study scalability, availability, and backend components.

2. Practice Real-World Problems

  • LLD: Practice designing small systems like Parking Lots or Elevator Systems.
  • HLD: Practice designing large-scale systems like Instagram, Netflix, or URL Shorteners.

3. Understand Trade-offs

  • Analyze the pros and cons of your designs.
  • Compare your solutions with others to identify improvements.

4. Mock Interviews

  • Simulate real interview scenarios with peers or mentors.
  • Focus on clear communication and justifying your design choices.

5. Resources

  • Books: Designing Data-Intensive Applications by Martin Kleppmann.
  • Videos: Watch system design tutorials on platforms like YouTube.
  • Open Source: Study the documentation of tools like Kafka, Redis, and databases.

Example Problems for Practice

Low-Level Design Problems:

  1. Design a Parking Lot System.
  2. Create a Library Management System.
  3. Design an Elevator Control System.
  4. Build a Vending Machine System.

High-Level Design Problems:

  1. Design Instagram or Twitter.
  2. Create a URL Shortening Service.
  3. Build a Distributed Job Scheduler.
  4. Design a Payment Gateway.
  5. Create a Netflix-like Streaming Service.

Another Format for System Design Interviews

You need to understand that there is a flow to the System design interview. Which mostly looks like this:

  1. Requirement clarification - functional & non-functional
  2. Estimations - Storage, Bandwidth, etc.
  3. Data flow
  4. High-level component design
  5. Detailed design
  6. Identify and address issues (System bottlenecks)

Detailed Interview Steps

1. Problem Statement

  • Functional Requirements
  • Non-Functional Requirements

2. Back of the Envelope Estimate

  • Estimating Queries Per Second
  • Read vs. Write Characteristics
  • Query Distribution Ratio
  • Breaking Down Query Distribution
  • Estimating Data Storage

3. API Design

  • Define different API endpoints to support the requirements

4. Database Design

  • Identifying Queries
  • Record Size Estimation
  • Schema Design
  • Sharding Approach
  • Selecting the right Database
  • Data Partitioning and related problems

5. High Level Design

  • Create component level design to show what system will look like
  • Use tools like Excalidraw for diagrams

6. Technology-Specific Designs

Design with Sorted Set Redis

  • Read/Write Access Pattern
  • Query Pattern

Design with Cassandra

  • Read/Write Access Pattern
  • How token-aware driver works
  • Query Pattern

7. Maintaining System Reliability

  • Address points to support this part of the system

References

Basic/Fundamental of System Design

Roadmap

Final Tips for Success

  1. Ask Questions: Clarify requirements and constraints before starting.
  2. Think Aloud: Communicate your thought process clearly.
  3. Iterate: Start with a basic design and refine it step by step.
  4. Focus on Trade-offs: No design is perfect; justify your choices.
  5. Practice, Practice, Practice: The more you practice, the better you’ll get.
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