A handbook for software systems

Understand the systems behind software.

Complex systems. Clear thinking.

Learn how engineering systems work, where they fail, and how to make sound design decisions.

Explore the handbook Start with CAP Theorem →

FIG. 01 — PACELC PARTITION TRADE-OFFS

Less boilerplate. More understanding.

01 Learn the idea02 Follow the visual03 Know the limits

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Find your starting point

Explore the handbook

01 / FOUNDATIONS

Core concepts

The building blocks. Explained clearly.

Consistent Hashing Leader Election Patterns In-Memory Caching Architecture CAP Theorem & PACELC

All 200 concepts →

02 / PUT IT TO WORK

System problems

Real requirements. Concrete designs.

Design a Distributed Rate Limiter Design a URL Shortener Design a Distributed Key-Value Store Design a Scalable Notification Service

All 109 problems →

03 / THE BIG PICTURE

Architecture domains

Patterns in the context that matters.

System Design Distributed Systems Software Architecture Algorithms & Data Structures

All 10 domains →

04 / INTERVIEW PREP

Interview prep

How to structure, reason, and prepare.

High-Level System Design Architectures: Chat, Streaming & Distributed Platforms Low-Level System Design: LRU Cache, Elevator & Ticket Booking Core Algorithm Patterns: Two Pointers, Fast & Slow, Sliding Window & DP Interview Prep Roadmaps

Practice interviews →

★ Featured ConceptFeatured concept

Asynchronous log fan-out and idempotency

Decouple microservices using durable commit logs, consumer group offsets, and dead-letter queue poison message handling.

Follow the event log

CONCEPT ARCHITECTURE FLOW

PublishKafka Log

PartitionConsumer

CommitOffset Ack

Learn by doing

Choose a practical track

High-level design / HLD

Connect services, data, and scale.

Design a Distributed Rate Limiter ↗Design a Scalable Notification Service ↗

Low-level design / LLD

Turn requirements into clean abstractions.

Implement a Thread-Safe LRU Cache ↗Bounding Task Queues to Prevent Heap OOM ↗

Algorithms & coding

Make the logic work, then make it efficient.

Course Schedule: Cycle Detection & Topological Sort ↗Top K Frequent Elements ↗