Course Index

01

How to Approach a System Design Interview

The 4-step framework: requirements → estimation → high-level design → deep dive

📚 Alex Xu Vol 1, Ch 3

Start here → 02

Back-of-the-Envelope Estimation

QPS, storage, bandwidth — the math that earns you credibility in the first 5 minutes

📚 Alex Xu Vol 1, Ch 2 · DDIA §1

→ 03

Scaling from Zero to Millions of Users

Single server → vertical/horizontal scaling → CDN, cache, DB replication — the full journey

📚 Alex Xu Vol 1, Ch 1

→ 04

Networking, DNS & Proxies

DNS resolution, TCP/UDP, HTTP/2, reverse proxies, latency numbers every dev should know

📚 System Design Primer · Hussein Nasser

→ 05

Load Balancing

L4 vs L7, round-robin, least connections, health checks, sticky sessions

📚 System Design Primer · Gaurav Sen

→ 06

CAP Theorem & Consistency Models

CP vs AP, strong vs eventual consistency, real-world trade-offs — the lens for every database choice

📚 DDIA §5, §9 · Alex Xu Vol 1, Ch 6

→ 07

Databases: SQL vs NoSQL

ACID, BASE, relational vs document vs wide-column vs graph — when to use what

📚 DDIA §2–3 · Alex Xu Vol 1, Ch 1

→ 08

Database Scaling: Replication & Sharding

Read replicas, leader-follower, horizontal partitioning, shard keys, rebalancing

📚 DDIA §5–6 · Alex Xu Vol 1, Ch 1

→ 09

Consistent Hashing

Hash rings, virtual nodes, minimal disruption — the algorithm behind distributed caches, databases, and load balancers

📚 Alex Xu Vol 1, Ch 5 · DDIA §6

Key pattern → 10

Caching

Cache-aside, write-through, write-back, CDNs, Redis/Memcached, eviction policies, cache invalidation

📚 Alex Xu Vol 1, Ch 1 · System Design Primer

→ 11

Message Queues & Async Processing

Kafka, RabbitMQ, pub/sub, event-driven architecture, backpressure, at-least-once vs exactly-once

📚 DDIA §11 · Alex Xu Vol 2, Ch 4

→ 12

API Design

REST, GraphQL, gRPC, rate limiting, pagination, idempotency, versioning — the contract between services

📚 Alex Xu Vol 1 · ByteByteGo

→ 13

Unique ID Generation & Distributed Coordination

Snowflake IDs, UUIDs, Zookeeper, leader election, distributed locks

📚 Alex Xu Vol 1, Ch 7

→ 14

Storage: Blob Storage & Object Stores

S3, HDFS, block vs object storage, CDN integration, upload/download flows

📚 Alex Xu Vol 2, Ch 9

→ 15

Search & Indexing

Inverted indexes, Elasticsearch, full-text search, geospatial indexing (geohash, quadtrees)

📚 DDIA §3 · Alex Xu Vol 2, Ch 1

→ 16

Rate Limiting

Token bucket, sliding window, leaky bucket, distributed rate limiting, API gateway patterns

📚 Alex Xu Vol 1, Ch 4

→ 17

Monitoring & Observability

Metrics, logging, tracing, alerting, SLIs/SLOs/SLAs — proving your system works

📚 Alex Xu Vol 2, Ch 5 · DDIA §1

→ 18

Design a URL Shortener

Hashing, base62 encoding, read-heavy workload, analytics — the "hello world" of system design

📚 Alex Xu Vol 1, Ch 8

Case Study → 19

Design a Rate Limiter

Algorithms in practice, distributed challenges, middleware integration, race conditions

📚 Alex Xu Vol 1, Ch 4

Case Study → 20

Design a Key-Value Store

Consistent hashing, Merkle trees, quorum reads/writes, gossip protocol, conflict resolution

📚 Alex Xu Vol 1, Ch 6 · DDIA §5–6

Case Study → 21

Design a Notification System

Push, SMS, email — fan-out, templates, delivery guarantees, priority queues, deduplication

📚 Alex Xu Vol 1, Ch 10

Case Study → 22

Design a News Feed (Twitter / Instagram)

Fan-out on write vs read, feed ranking, social graph, timeline cache, celebrity problem

📚 Alex Xu Vol 1, Ch 11

Case Study → 23

Design a Chat System (WhatsApp / Slack)

WebSockets, presence, message ordering, group chat, read receipts, offline delivery

📚 Alex Xu Vol 1, Ch 12

Case Study → 24

Design Search Autocomplete

Trie data structure, top-K suggestions, ranking by frequency/recency, low-latency serving

📚 Alex Xu Vol 1, Ch 13

Case Study → 25

Design YouTube / Video Streaming

Upload pipeline, transcoding DAG, CDN, adaptive bitrate, recommendations

📚 Alex Xu Vol 1, Ch 14

Case Study → 26

Design Google Drive / Dropbox

File sync, block-level deduplication, conflict resolution, notification service, metadata DB

📚 Alex Xu Vol 1, Ch 15

Case Study → 27

Design Google Docs (Collaborative Editing)

Operational Transformation, CRDTs, WebSockets, cursor presence, version history

📚 DDIA §5 · DesignGurus

Case Study → 28

Interview Practice & Self-Assessment

Timed mock exercises, common mistakes, evaluation rubric, curveball handling, what's next

📚 Hello Interview · Exponent

Final lesson →