System Design

How real systems are actually built at scale, one architecture at a time: the constraints, the tradeoffs, and the decisions behind each one. Read them in any order.

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How WhatsApp Works: The Architecture Behind 100B Messages a Day

Beginner · 5 min read
1

How Slack Works: Workspace-Sharded Architecture at Scale

Beginner · 4 min read
2

How YouTube Works: Transcode Once, Serve From Edge

Beginner · 4 min read
3

How Stripe Works: Idempotent API Over an Append-Only Ledger

Beginner · 4 min read
4

How Spotify Works: Audio CDN Plus Nightly Recommendation

Beginner · 3 min read
5

How Instagram Works: Fanout-on-Write With Celebrity Exception

Beginner · 3 min read
6

How Twitter Timeline Works: Hybrid Fanout Architecture

Beginner · 3 min read
7

How Uber Finds Nearby Drivers: H3 Hex Grid Architecture

Intermediate · 4 min read
8

How ChatGPT Works: KV-Cache, GPU Cluster, and the Router

Intermediate · 3 min read
9

How Reddit Works: Python Monolith Plus 90% Varnish Cache

Intermediate · 3 min read
10

How Airbnb Works: Calendar as a Consistency Boundary

Intermediate · 3 min read
11

How Zoom Works: SFU Beats MCU at Scale

Intermediate · 3 min read
12

How Amazon Lambda Works: Firecracker MicroVMs at Scale

Intermediate · 3 min read
13

How Google Docs Works: Operational Transformation at Scale

Advanced · 3 min read
14

How Tinder Works: Asymmetric Match Graph at Scale

Advanced · 3 min read
15

How Apple AirTags Work: Encrypted Crowd-Sourced Finding

Advanced · 4 min read
16

How Bluesky Works: AT Protocol and Portable Identity

Advanced · 3 min read
17

How Cloudflare Scaled Postgres: SQL at the Edge

Advanced · 3 min read
18

How Meta Serverless Works: TwSF and Bin ACL at FB Scale

Advanced · 3 min read