Design the system.Defend every choice.
An animated, long-form curriculum for learning why an architecture works, what alternatives were rejected, and how invariants, bottlenecks, failures, and cost shape each choice.
Build the mental model in four moves.
Start with a compact read-heavy service, add distributed enforcement, learn ordered logs, then finish with a correctness-critical transaction system.
URL Shortener
IDs, cache-aside reads, partitioning, and asynchronous analytics.
02 · Protect the edgeRate Limiter
Distributed counters, failure policy, atomic updates, and tenant fairness.
03 · Reason about orderMessage Queue
Partitions, durability, replication, consumer groups, and replay.
04 · Protect the invariantPayment System
Idempotency, state machines, double-entry ledgers, and reconciliation.
60 systems. No hand-waving.
Filter by architecture family or search for a concept. Every design explains why the architecture was selected, rejected alternatives, trade-offs, evolution triggers, failure analysis, and answer guidance.
URL Shortener
Create compact links, resolve them globally, and count clicks without slowing redirects.
Rate Limiter
Protect APIs with predictable quotas across a distributed fleet.
Notification System
Deliver push, email, and SMS reliably while respecting preferences and provider limits.
File Storage & Sharing
Upload, sync, version, and share large files with durable metadata and blob storage.
Chat & Messaging
Deliver ordered messages, receipts, presence, and offline sync at global scale.
News Feed
Generate ranked, paginated feeds while absorbing celebrity fan-out.
Social Post Service
Create posts, media, follows, and public timelines with clear consistency boundaries.
Video Streaming Platform
Ingest videos, transcode variants, and stream globally with adaptive bitrate playback.
Ride-Hailing Service
Track drivers, match nearby supply, and manage trips as a consistent state machine.
Ticket Booking
Reserve scarce seats under extreme contention without double booking.
API Gateway
Authenticate, route, protect, and observe traffic without becoming a single failure domain.
Distributed Cache
Serve low-latency reads with partitioning, eviction, replication, and predictable failure behavior.
Job Scheduler
Run delayed, recurring, and retryable work exactly when business semantics require.
Web Crawler
Fetch the web politely, deduplicate URLs, and scale parsing and storage independently.
Search Autocomplete
Return relevant prefix suggestions in milliseconds while trends change continuously.
Logging & Monitoring
Ingest, index, retain, query, and alert on telemetry under bursty load.
Metrics Collection
Collect high-cardinality time series, aggregate them, and evaluate alerts reliably.
Distributed Key-Value Store
Partition, replicate, and reconcile key-value data through failures and topology changes.
Payment Processing
Accept money with idempotency, an auditable ledger, and reconciliation across unreliable partners.
Shopping Cart & Checkout
Coordinate carts, inventory, pricing, orders, and payments without distributed transactions.
Collaborative Document Editor
Merge concurrent edits, broadcast presence, and persist recoverable document history.
Cloud Object Storage
Store immutable objects with multipart upload, replication, versioning, and extreme durability.
Distributed Message Queue
Provide ordered partitions, durable retention, consumer groups, and replayable offsets.
Feature Flag Service
Evaluate flags locally at low latency while configuration changes propagate safely.
Recommendation System
Collect behavior, train representations, retrieve candidates, and rank them online.
Fraud Detection Pipeline
Score risky events in real time while preserving explainability, audit, and model evolution.
Configuration Management
Version, validate, watch, and roll out configuration without taking services down.
Distributed Lock Service
Coordinate exclusive work using leases and fencing rather than trusting process ownership.
Multi-Tenant SaaS
Isolate tenants across identity, data, compute, quotas, and operations.
Unique ID Generator
Generate sortable, globally unique identifiers without a central database bottleneck.
Parking Lot
Model entrances, spots, tickets, pricing, and concurrent allocation across floors.
Elevator System
Schedule cars, serve hall and cabin requests, and preserve safety under concurrent events.
Library Management
Manage catalog items, copies, members, holds, loans, fines, and notifications.
Meeting Room Scheduler
Find rooms, reserve time ranges, invite attendees, and prevent overlapping bookings.
ATM
Authenticate users, dispense cash, and coordinate account transactions with device state.
Vending Machine
Accept payment, select products, dispense inventory, return change, and recover faults.
Chess or Card Game
Represent legal moves, turns, game state, persistence, and optional multiplayer synchronization.
Logging Framework
Design structured logging APIs, levels, appenders, formatting, buffering, and rotation.
In-Memory LRU Cache
Provide O(1) get/put, eviction, capacity control, and optional expiration safely.
Task Management System
Model projects, tasks, assignment, status workflows, dependencies, comments, and audit history.
Web Search Engine
Crawl, index, rank, and serve the open web with fresh, trustworthy results.
Email Service
Accept, route, store, filter, and synchronize email across unreliable external domains.
Live Streaming Platform
Ingest live video, transcode continuously, and deliver low-latency playback to massive audiences.
Advertisement Serving
Select eligible ads, pace budgets, and record billable events within a strict latency budget.
Stock Exchange
Accept orders, match deterministically, publish market data, and preserve an auditable ledger.
Food Delivery Marketplace
Coordinate menus, orders, restaurants, couriers, dispatch, and settlement in real time.
Hotel Reservation Platform
Search inventory and reserve room-night capacity without overselling across channels.
Digital Wallet
Hold balances, transfer value, enforce limits, and reconcile funding rails safely.
Expense Sharing
Model groups, split strategies, debts, settlements, and simplified balances without losing history.
Online Auction
Run timed auctions, enforce bid ordering, extend deadlines, and settle winners consistently.
Maps and Navigation
Serve maps, geocode places, compute routes, and update travel times from live traffic.
Service Discovery
Register instances, publish health-aware endpoints, and provide stable discovery through partitions.
Secrets Management
Store, authorize, rotate, lease, and audit secrets without exposing plaintext broadly.
CI/CD Platform
Trigger reproducible builds, schedule isolated runners, preserve artifacts, and deploy safely.
Package Registry
Publish immutable packages, resolve versions, scan artifacts, and distribute them globally.
Workflow Orchestrator
Run durable multi-step workflows that survive retries, timers, worker crashes, and long waits.
Distributed SQL Database
Provide SQL transactions over sharded, replicated data with online rebalancing.
Identity and Authentication
Authenticate humans and services, issue sessions/tokens, enforce MFA, and revoke compromised access.
Spreadsheet Engine
Model cells, formulas, dependencies, recalculation, cycles, and collaborative edits.
File System
Design files, directories, inodes, block allocation, journaling, caching, and crash recovery.