Le Systems
Master system design and AI concepts through interactive visualizations and quizzes. Built for engineers pursuing mastery.
Core Topics
Deep dives into essential technologies and concepts.
System Design Framework
Master the structured approach senior engineers use to design any system — from clarifying requirements to defending trade-offs. Not memorized solutions, but a repeatable methodology for any problem.
Basics: Large Language Models
Transformer architecture, training pipelines, inference optimization, and production deployment — from attention heads to serving at scale.
Deep Dive: PostgreSQL
Master PostgreSQL internals from the ground up — MVCC, WAL, indexes, query planning, and replication, based on actual source code analysis.
Deep Dive: Redis
Master Redis from the ground up — data structures, persistence, replication, cluster mode, and production patterns, based on actual source code analysis.
Non-Functional Requirements
Master the essential NFRs that make or break system designs — CAP theorem, consistency models, scalability, caching, load balancing, and resilience patterns with interactive tradeoff exploration.
Deep Dive: Java & Spring Boot
Master Java from JVM internals to Spring Boot microservices — OOP, SOLID, design patterns, concurrency, and production architecture for mastery.
Deep Dive: Docker & Kubernetes
Master containerization and orchestration — from Docker internals to Kubernetes architecture, networking, scheduling, and production patterns.
Coming SoonDeep Dive: Distributed Consensus
Master consensus algorithms from Paxos to Raft — leader election, log replication, membership changes, and how systems like etcd, ZooKeeper, and CockroachDB achieve agreement.
Coming SoonConsistency Models
Deep dive into distributed consistency — strong, eventual, causal, and linearizable models with interactive replication timelines and conflict resolution visualizations.
Coming SoonData Structures & Algorithms
A deep dive into data structures and algorithms for senior engineer interviews — from complexity analysis and hash table internals to graph algorithms, dynamic programming, and advanced problem-solving patterns.
Deep Dive: Product Manager
Master product management from strategy to execution — metrics frameworks, prioritization, experimentation, cross-functional leadership, and platform thinking at scale.
Foundations
Core building blocks every system design builds upon.
Intermediate System Design: The Decision Framework
Master the 30 critical architectural decisions behind distributed systems. A tree-picker approach with tradeoffs, tool comparisons, and real-world examples — solve 80% of system design interviews.
Design a URL Shortener
Apply the system design framework to build a production-grade URL shortening service — from requirements gathering to scaling for 100M users.
Design a Rate Limiter
Learn how to protect APIs from abuse and overload by designing a production-grade rate limiter — from single-server token buckets to distributed systems with Redis.
Design a Key-Value Store
Design a distributed key-value store from scratch — from single-node hash tables to replicated, partitioned systems that serve millions of requests per second with tunable consistency.
Design a Unique ID Generator
Design a distributed unique ID generator that produces globally unique, sortable identifiers at scale — from UUIDs to Snowflake IDs and beyond.
Consistent Hashing
Master consistent hashing — the algorithm behind distributed caches, databases, and CDNs that minimizes data movement when nodes join or leave a cluster.
Storage & Databases
Data storage patterns from caches to columnar analytics engines.
Design a Distributed Cache
Master distributed caching from the ground up — cache strategies (read-through, write-through, write-behind), eviction policies (LRU, LFU, FIFO), consistency models, Redis vs Memcached trade-offs, and production patterns for cache stampede prevention.
Design Object Storage
Understand how object storage systems like S3 work — S3-style API design, metadata management, replication for 11 nines of durability, erasure coding, lifecycle policies, tiering, and multi-region scaling.
Design a Distributed File System
Deep dive into distributed file systems — GFS/HDFS architecture, master/NameNode design, chunk storage and replication, read/write pipelines, fault tolerance, and modern alternatives like Ceph and MinIO.
Relational Database Scaling
Master the art of scaling relational databases — read replicas, vertical vs horizontal scaling, sharding strategies, shard key selection, cross-shard queries, schema migrations at scale, and connection pooling.
Time-Series Databases
Understand time-series data patterns — write-optimized architectures, compression and encoding, retention and downsampling, query patterns, InfluxDB/TimescaleDB/Prometheus comparison, and real-world monitoring use cases.
Design a Search Engine
Master search engine internals — inverted indexes, tokenization and analysis, TF-IDF and BM25 scoring, distributed search with Elasticsearch, index sharding, query processing pipelines, autocomplete, and fuzzy search.
Columnar Databases
Understand column-oriented storage — row vs column storage, compression techniques, vectorized query execution, partitioning and sorting, BigQuery/Redshift/ClickHouse comparison, star schema modeling, and OLAP vs OLTP trade-offs.
Messaging & Streaming
Async communication, event-driven architectures, and log-based systems.
Deep Dive: Apache Kafka
Master Kafka from the ground up — core architecture to deep internals, based on actual source code analysis.
Design a Message Queue
Design a distributed message queue from scratch — producer-consumer patterns, delivery guarantees, dead letter queues, backpressure, and RabbitMQ architecture deep dive.
Design a Pub/Sub System
Design a publish-subscribe messaging system — topic-based and content-based routing, fan-out patterns, ordering guarantees, push vs pull delivery, and Google Cloud Pub/Sub deep dive.
Design a Task Queue
Design a distributed task queue — worker pools, priority scheduling, retry logic, task chaining, rate limiting, and deep dives into Celery, Sidekiq, and Bull architectures.
Distributed Transaction Log
Design a distributed transaction log — append-only architecture, log segmentation, distributed replication, consensus protocols, CDC, and log-based messaging at scale.
Infrastructure
The platform layer: gateways, discovery, config, tracing, and secrets.
Content Delivery Networks
Master how CDNs reduce latency by serving content from edge servers worldwide — caching strategies, cache invalidation, push vs pull models, edge computing, and CDN security.
Load Balancing
Master load balancing from fundamentals to global scale — algorithms, health checks, session persistence, SSL termination, and multi-region strategies.
Design an API Gateway
Master API gateway architecture from request routing and authentication to rate limiting, circuit breakers, and production patterns with Kong, Envoy, and AWS API Gateway.
Service Discovery
Understand how microservices find each other at scale — client-side vs server-side discovery, service registries, health checking, DNS-based discovery, and service mesh integration.
Distributed Config System
Design a centralized configuration system for distributed services — watch-based push notifications, versioning and rollback, feature flags, and consistency trade-offs across etcd, Consul, and ZooKeeper.
Distributed Tracing
Master distributed tracing from the trace/span model and context propagation to sampling strategies, Jaeger/Zipkin internals, OpenTelemetry, and correlation with logs and metrics.
Secrets Management
Design a secrets management system from Vault architecture and seal/unseal to dynamic secrets, encryption as a service, access policies, secret rotation, and cloud provider integration.
AWS Solutions Architect Associate
Master the AWS SAA-C03 exam — VPC networking, S3 storage classes, RDS/DynamoDB, high availability with ELB/ASG, IAM security, serverless with Lambda, and Well-Architected Framework design patterns.
Real-time & Communication
Low-latency systems for live collaboration, gaming, and video.
Design a Chat System
Design a real-time chat system like WhatsApp, Slack, or Discord — from WebSocket connections and message delivery to presence indicators, group chat fan-out, and offline sync at scale.
Design a Notification System
Design a scalable notification system from scratch — push, email, SMS, and in-app channels with message queues, delivery pipelines, user preferences, and reliability patterns.
Design a Live Comments System
Design a real-time live comments feed like YouTube Live Chat, Twitch Chat, or Instagram Live — from WebSocket fan-out and message ordering to content moderation pipelines, hot partition handling, and scaling to millions of concurrent viewers.
Design Collaborative Editing
Design a real-time collaborative editor like Google Docs, Figma, or Notion — from CRDTs and Operational Transform to cursor presence, version history, conflict resolution, and scaling to thousands of concurrent editors.
Design a Multiplayer Game Server
Design a multiplayer game server architecture like Fortnite, Valorant, or Rocket League — from client-server networking and state synchronization to lag compensation, matchmaking, tick rate, anti-cheat, and regional deployment.
Design Video Conferencing
Design a video conferencing system like Zoom, Google Meet, or Microsoft Teams — from WebRTC fundamentals and signaling servers to SFU/MCU architectures, media processing, bandwidth adaptation, recording, and scaling to large meetings.
ML & Data Systems
End-to-end machine learning infrastructure and data platforms.
Design a Recommendation Engine
Build Netflix/YouTube-scale recommendation systems — collaborative filtering, embeddings, real-time ranking, and A/B testing personalization at millions of QPS.
Design a Feature Store
Master ML feature management — online/offline stores, point-in-time correctness, feature pipelines, and low-latency serving with Feast/Tecton patterns.
Design an ML Training Pipeline
Architect distributed training systems — data parallelism, model parallelism, hyperparameter tuning, experiment tracking, and GPU cluster orchestration.
Design ML Serving/Inference
Build low-latency inference systems — model optimization, canary deployments, auto-scaling GPU clusters, and monitoring for drift and degradation.
Design Stream Processing
Master real-time data processing — windowing semantics, stateful computation, exactly-once guarantees, watermarks, and Flink/Spark Streaming architectures.
Design a Data Warehouse Pipeline
Architect analytics data systems — ETL/ELT pipelines, dimensional modeling, slowly changing dimensions, and modern cloud warehouse patterns with BigQuery/Snowflake.
Design an A/B Testing Platform
Build experimentation infrastructure — statistical frameworks, traffic splitting, metric pipelines, sequential testing, and multi-armed bandits at scale.
Product Systems
Full product designs: search, video, ride-sharing, ads, and more.
Design a News Feed
Master the architecture behind Facebook, Twitter, and LinkedIn feeds — from fan-out strategies and ranking algorithms to real-time delivery at scale.
Design a Payment System
Design a production-grade payment system from scratch — payment processing flows, idempotency, double-entry ledgers, refunds, reconciliation, PCI compliance, and scaling to millions of transactions.
Design a Web Crawler
Architect a distributed web crawler that discovers, downloads, and deduplicates billions of pages — covering URL frontier scheduling, politeness policies, content fingerprinting, and horizontal scaling.
Design Instagram / Photo Sharing
Architect a photo-sharing platform like Instagram — from upload pipelines and CDN distribution to feed generation with fan-out strategies, social graph storage, and scaling to billions of photos.
Design YouTube / Video Platform
Architect a video platform like YouTube — from upload and transcoding pipelines to adaptive bitrate streaming, recommendation engines, and scaling to billions of daily views.
Design a Ride-Sharing Platform
Architect Uber/Lyft from the ground up — real-time location tracking, geospatial indexing, driver-rider matching, ETA calculation, surge pricing, and scaling across cities worldwide.
Design a Hotel/Flight Booking System
Architect a booking platform like Booking.com or Expedia — inventory management, search pipelines, dynamic pricing, double-booking prevention, and payment integration at scale.
Design an Ad Click Aggregator
Architect a real-time ad click aggregation system — event collection, stream processing, deduplication, time-window aggregation, fraud detection, and reconciliation at billions of events per day.
Design E-commerce Search
Architect a product search system like Amazon — query understanding, faceted filtering, learning-to-rank, personalization, typeahead autocomplete, and scaling to millions of products.
Daily Challenge
Test your knowledge — a new question every day
In BM25, what happens when the parameter b is set to 0?
Stay Updated
Get notified when new topics and visualizations drop.