📁 LLD-HLD 📁 Roadmap 🏷️ System-Design 🏷️ Interview-Prep

📝 Topics Covered

  1. 1. When to Start Learning System Design
    • Video walkthrough & baseline expectations
  2. 2. High-Level Design (HLD)
    • Macro plans, blueprints, and business integration
  3. 3. Low-Level Design (LLD)
    • Micro-planning, class layouts, and actionable components
  4. 4. Differences Between HLD and LLD
    • 4.1 HLD vs. LLD Focus Areas
    • 4.2 Macro vs. Micro Architecture
    • 4.3 Development Chronology
    • 4.4 Target Audience
  5. 5. System Design (HLD & LLD) Roadmaps
    • 5.1 7-Week Step-by-Step Study Guide
    • 5.2 Transitioning from HLD to LLD
  6. 6. Recommended Reading (System Design Books)

The Software Development Life Cycle (SDLC) flows through various systematic phases such as requirements analysis, feasibility study, design, coding, and testing. Each phase is further divided into dedicated tasks with well-defined objectives and outcomes.

Design Analysis is the crucial phase where the actual architecture, working modules, data models, and execution pathways of a software product are established.

Two vital steps in this phase are High-Level System Design (HLD) and Low-Level System Design (LLD).

1. When to Start Learning System Design?

Determining when to introduce system design into your developer journey is essential for career growth:

  • Prerequisites: Start anytime after mastering core data structures, algorithms, and object-oriented programming (OOP) principles.
  • No Gatekeeping: There is no requirement to wait for a specific year mark—begin exploring as soon as your programming fundamentals are solid.

Career Leveling & Interview Expectations

Level Experience Expected Interview Focus
SDE-1 (Junior) 0 - 2 Years Focused primarily on data structures, algorithms, and solid problem-solving. Typically no system design rounds.
SDE-2 (Mid-Level) 2 - 4 Years Focused heavily on Low-Level Design (LLD) (e.g. object-oriented design patterns, machine coding, and clean classes/interfaces).
SDE-3+ (Senior) 5+ Years Expected to excel at both High-Level Design (HLD) (distributed systems, scaling, microservices) and Low-Level Design (LLD).

💡 SDE-2 Interview Insights (2–4 Years Exp)

  • LLD Focus: Expect requests to design concrete, mini-applications (e.g. Design a Parking Lot, Design a Movie Ticket Booking System, or Design a Logger System).
  • Deliverables: You will need to draw UML diagrams, structure clean class relations, define strict interfaces, and write functional, error-free code.
  • Negotiating Strategy: If you lack extensive real-world, large-scale distributed system experience, be honest. Negotiate to focus the interview on clean code and LLD rather than complex HLD architectures.

🚀 SDE-3+ Interview Insights (5+ Years Exp)

  • Dual Design Rounds: Expect deep-dive, multi-hour rounds covering both broad, high-level architectures and fine-grained, low-level component classes.
  • Impact Over Years: The interview shifts away from years on your resume to actual technical leadership, technical ownership, and project growth.

Watch the quick breakdown below:

2. High-Level Design (HLD)

High-Level Design (HLD) provides a comprehensive overview of the software development process. It focuses on the macro architecture, identifying the major systems, applications, data stores, external APIs, and the overarching navigational flow of the product.

📋 The Architectural Blueprint: Think of HLD as the architectural blueprint. It maps out how different large-scale components (e.g., frontend, microservices, databases, caches) will interact, and how business requirements translate directly into a scalable, high-performance system topology.

3. Low-Level Design (LLD)

Low-Level Design (LLD) focuses on the detailed planning, class design, and implementation of individual components and modules defined in the HLD.

🛠️ The Implementation Blueprint: Each macro module in an HLD has a corresponding LLD document. LLD provides highly detailed schemas, including UML class diagrams, method signatures, design patterns, and database tables, giving software engineers a clear, actionable guide to write clean, maintainable code.

4. Differences Between HLD and LLD

4.1 HLD vs. LLD Focus Areas

Focus Area High-Level Design (HLD) Low-Level Design (LLD)
System View Macro Architecture (Systems & Services) Micro Architecture (Classes & Interfaces)
Primary Focus Scalability, Availability, & CAP Trade-offs Maintainability, Extensibility, & Code Quality
Key Tools Block Diagrams, Data Flows, Cloud Topologies UML Diagrams, Class Models, Sequence Flows
Core Standards System Integration, Protocols, CDN/Caches SOLID Principles, Design Patterns, OOP Concepts
Interviews System Architecture Interviews Machine Coding & Object-Oriented Design (OOD)

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4.2 Macro vs. Micro Architecture

  • HLD (Macro): Offers a high-level view of the system. It deals with server clusters, database types, service networks, load distribution, and general data flows.
  • LLD (Micro): Deals with the software internals. It outlines exactly how class loops, inheritance chains, interfaces, error handling, and method signatures behave inside a single service unit.

4.3 Development Chronology

  • HLD Precedes LLD: High-Level Design must be finalized and approved before starting LLD drafting. HLD begins immediately after business requirements gathering and system analysis phases are complete.
  • LLD Dependency Sequence: Low-Level Designs depend directly on the approved parent HLD. They must be drafted in a logical order, as child class dependencies rely on core data models defined in previous LLD iterations.
  • SDLC Phases:
    • HLD directly maps to the System Analysis & High-Level Architecture phase.
    • LLD directly maps to the Detail Design & Active Coding phases.

4.4 Target Audience

  • HLD Audience: Crafted for System Architects, Engineering Managers, Product Owners, and business stakeholders who need to understand what the system does and how it connects globally.
  • LLD Audience: Crafted for Software Developers, Code Reviewers, and QA Automation Engineers who need to understand exactly how to write, test, and maintain the codebase.

5. System Design (HLD & LLD) Roadmaps

To guide your study path, use these curated roadmap topics:

  1. Software Design & Architecture Roadmap
  2. UML & Class Diagram Guides
  3. Software Design Best Practices
  4. System Design Case Studies

5.1 7-Week Step-by-Step Study Guide

Follow this week-by-week curriculum to build a solid foundation in high-level and low-level system design:

🔹 Week 1: Core Architectures & Networks

  • Introduction: Key concepts of system scalability and design patterns.
  • Clients & Servers: Request-response loops, static assets, and dynamic routing.
  • Monoliths vs. Microservices: Monolithic applications vs. decoupled service meshes.
  • gRPC & Protobuf: High-performance RPC frameworks vs. traditional REST APIs.
  • Network Protocols: HTTP/1.1, HTTP/2, HTTP/3, TCP/IP, and WebSockets.
  • Proxies & Gateways: Reverse proxies (Nginx, HAProxy) and API gateways.

🔹 Week 2: Scalability, Caching & Message Queues

  • Scaling: Horizontal scaling (adding nodes) vs. vertical scaling (adding CPU/RAM).
  • Load Balancers: Round-robin, least connections, IP hash, and dynamic algorithms.
  • Caching Systems: Redis, Memcached, cache eviction policies (LRU, LFU, FIFO), and write-back/write-through strategies.
  • Asynchronous Processing: Task queues and event-driven architectures.
  • Message Brokers: Publisher-subscriber pipelines using Kafka, RabbitMQ, or Amazon SQS.

🔹 Week 3: Performance, Availability & CAP Theorem

  • Performance Metrics: Decoupling latency, throughput, bandwidth, and response times.
  • CAP Theorem: Consistency vs. Availability vs. Partition Tolerance (CP vs. AP).
  • Resiliency: Fault tolerance, retry policies, backoff algorithms, and circuit breakers.

🔹 Week 4: Databases & Storage Systems

  • Memory vs. Storage: RAM/SSD caches vs. relational/non-relational persistent storage.
  • Replication Systems: Synchronous vs. asynchronous replication; Single-master vs. Multi-master cluster synchronization.
  • RAID Arrays: Storage efficiency and fault tolerance using RAID 0, 1, 5, 6, and 10.

🔹 Week 5: Database Partitioning & Advanced Paradigms

  • Partitioning: Vertical partitioning (normalization) vs. horizontal partitioning (database sharding).
  • Consistent Hashing: Distributed hashing algorithms for elastic caches and ring topologies.
  • Specialized Storage: Document databases, wide-column stores, time-series DBs, and graph databases.
  • Migration: Schema-less migrations and zero-downtime DB cutovers.

🔹 Week 6: Capacity Estimation & API Design

  • Capacity Estimation: QPS calculation, network bandwidth limits, and storage estimates.
  • API Design: Designing query parameters, HTTP response codes, and clean RESTful guidelines.
  • Rate Limiting: Token bucket, leaky bucket, sliding window, and client throttling.
  • Security & Resilience: TLS encryption, CORS controls, OAuth2 validation, and rate protection.

🔹 Week 7: End-to-End Designs & Interview Strategies

5.2 Transitioning from HLD to LLD

Understanding how to bridge the gap between high-level components and low-level code structures is essential for developers. Review these detailed video tutorials:

To accelerate your learning curve, make sure to read these core books:

📚 Highly Recommended Reading List:

  1. Designing Data-Intensive Applications by Martin Kleppmann (The gold standard for distributed systems).
  2. System Design Interview – An Insider’s Guide by Alex Xu (Highly practical, interview-focused architectures).
  3. Solutions Architect’s Handbook by Saurabh Shrivastava (Great for cloud-focused designs).
  4. Fundamentals of Software Architecture by Mark Richards (A comprehensive guide to architecture styles and patterns).
  5. Operating Systems: Three Easy Pieces by Remzi Arpaci-Dusseau (Essential for low-level systems and storage understanding).

Reference