System Lab: watch systems work, then break

Live

Requests flow from Users through the balancer to three servers.

Response timetarget ≤ 400 ms: 400 ms
Cache hits: 80%
Failed: 0%

The route

Lines are topics; zones are levels. Ride the recommended path from N1, or jump to any station. A dimmed one is best after another.

NNetworkingWhat crosses the wire: a request, its answer, the acknowledgement, and what goes wrong on the way.

FFoundationsHow a request is served, and what happens when there are too many.

CCachingAnswer from a nearby copy instead of doing the work again.

DDataCopying and splitting data across machines, and what that costs.

AAsyncDo the work later, elsewhere, and survive the hiccups.

RResilienceStay up when clients misbehave, dependencies hang and traffic swings.

OOperatingChange a running system without breaking it: deploys, rollbacks and draining.

★JourneysReal systems that ride several lines.

AllBeginnerIntermediateAdvanced

Journeys

Real systems, built up stage by stage under growing traffic and failures. Each one rides several lines.

S0 Keep a URL shortener alive
Your link shortener is about to hit the front page. Grow it stage by stage and keep it fast through a surge, a viral link, a bot and a crash.
The lessons it rides
Ride it 4 stages · about 20 min
A design that holds stage 4, “Under attack”.
S1 Crawl the web
Fetch page after page from a slow, flaky web without losing a link to a crash or getting stuck on a dead site.
The lessons it rides
Ride it 4 stages · about 20 min
A design that holds stage 4, “Dead sites”.
S2 Serve a premiere to the world
Viewers on three continents press play in the same second. Every edge must keep up, even when one dies.
The lessons it rides
Ride it 4 stages · about 20 min
A design that holds stage 4, “Asia's edge dies”.
S4 Sell 1,000 seats to 100,000 people
Doors open and a hundred thousand people want a thousand seats. Sell each seat exactly once, and stay up.
The lessons it rides
Ride it 4 stages · about 20 min
A design that holds stage 4, “Everyone at once”.
S7 Charge exactly once
Charge a card once, even when the provider is slow, replies get lost and services fail halfway.
The lessons it rides
Ride it 4 stages · about 20 min
A design that holds stage 4, “A slow card network”.
S3 Keep a chat live
Every message must reach every user within a moment, as users pile in and a server freezes.
The lessons it rides
Ride it 4 stages · about 20 min
A design that holds stage 4, “A server freezes”.
S6 Build a news feed
Every feed gathers posts from hundreds of people. Build it when they post, or when you read it?
The lessons it rides
Ride it 4 stages · about 20 min
A design that holds stage 4, “A celebrity posts”.
S5 Match a rider to the nearest driver
Drivers ping their position every few seconds. Riders want the nearest one, and no driver may go to two riders.
The lessons it rides
Ride it 4 stages · about 20 min
A design that holds stage 4, “East goes dark”.
S8 Count a billion clicks
Count every ad click fast enough for a live dashboard, without losing or double-counting one.
The lessons it rides
Ride it 4 stages · about 20 min
A design that holds stage 4, “A counter crashes”.

How to read a scene

Every scene draws a request the same seven ways. Shape and colour both carry the state, so a scene reads without colour too.

Request. On its way, or waiting its turn.
Running late. Past the latency target and still going.
Answered. Heading back to the user with a good result.
Stale answer. Answered, but with out-of-date data.
Turned away. Refused fast on purpose: rate-limited or a fallback.
Failed. An error. Dropped requests fall off the stage.
Gave up. The user timed out. The work may still be running.

Watch systems work. Then watch them break.

The route

Short on time? The interview fast lane

Journeys

S0 Keep a URL shortener alive

The lessons it rides

S1 Crawl the web

The lessons it rides

S2 Serve a premiere to the world

The lessons it rides

S4 Sell 1,000 seats to 100,000 people

The lessons it rides

S7 Charge exactly once

The lessons it rides

S3 Keep a chat live

The lessons it rides

S6 Build a news feed

The lessons it rides

S5 Match a rider to the nearest driver

The lessons it rides

S8 Count a billion clicks

The lessons it rides

How to read a scene