1 · The client
One click, one request
Your browser asks for a page. It does not know yet where the server is.
A modern web page often triggers more than 50 requests.
NewThe course you kept asking for
Step into the maze of System Design
No slides, no hour-long video. You predict, you run the simulation, you watch the architecture hold or collapse. Room after room, you go from your first server to the architecture you defend in front of a review board.
30rooms
47simulations
233terms defined
5bosses
The common thread
Everything starts with a request
Follow it from the browser to the database: every stop is a room of the maze.
2 · The DNS
The Internet's phone book
The domain name becomes an IP address, in a few milliseconds.
Room 1: you learn to follow a request step by step.
3 · The CDN
Content close to home
Images and scripts are served from a nearby server, not from the other side of the world.
A Douala–Paris round trip costs about 100 ms. A local CDN, under 20.
4 · The load balancer
One door, many servers
It spreads the traffic and removes a failing server within seconds.
It is what lets you deploy without taking the site down.
5 · The servers
This is where the work happens
Stateless, they multiply at will on peak day.
Above 70% utilization, latency takes off.
6 · The cache
Short-term memory
It answers questions already asked in one millisecond.
A good cache spares the database 80 to 95% of reads.
7 · The database
Long-term memory
It keeps the orders and the money. It is often the first to crack.
Floor 3: you will learn to split it when one is no longer enough.
A game experience
You learn better when you play
Game mechanics in service of real engineering skill.
Live simulations
A real queueing model: capacity, latency, cascading failures. You watch the system live.
Debates with the team
Koffi the tech lead, Amina from marketing, an architecture board: learn to argue your case.
Build your architecture
Pick your components, stay on budget, send the traffic. If it breaks, try again.
Your written decisions (ADRs)
Every big choice becomes an Architecture Decision Record you can copy for your team.
Hearts, streaks and milli-Uptime
Hearts to protect, a daily streak to keep alive, milli-Uptime to earn, bosses to beat, badges to collect.
No jargon without a definition
Every technical term is clickable: a plain definition and a concrete example, right when you need it.
The path
Five floors, from your first server to the architecture board
Each floor prepares a Runbookly certification, from One Nine to Five Nines.
One Nine
Operator
Foundations
The journey of a request, latency, scaling and your first database.
The journey of a requestLatency, throughput and percentilesGrowing: vertical or horizontalThe load balancerDatabasesEstimate like an engineer👾 Boss: launch day
7rooms
Two Nines
Builder
The building blocks that carry the load
Cache, CDN, replication, message queues and APIs: the parts of every architecture.
CachingThe CDN: serving from close byReplicationMessage queuesDesigning an APIStateless servers👾 Boss: the URL shortener
7rooms
Three Nines
Engineer
Growing without breaking
Partitioning, consistency, rate limiting, resilience and observability.
Sharding the dataConsistency and the CAP theoremRate limitingSurviving cascading failuresSearchObserving your system👾 Boss: the star's evening
7rooms
Four Nines
Specialist
Production at scale
Availability, multi-region, distributed transactions, streaming, security and cost.
Availability, nine by nineMultiple regionsDistributed transactions: saga and outboxEvent streams and streamingSecurity in the architectureCost as an architecture requirement👾 Boss: a region goes down
7rooms
Five Nines
Architect
Designing and defending an architecture
Requirements, trade-offs, ADRs, splitting a monolith, design reviews and a full case study.
Starting from the requirementsThe art of the trade-offArchitecture Decision RecordsMonolith or microservices?Running a design reviewCase study: notifications👾 Final boss: the architecture board
7rooms
At the exit of the maze
What you will be able to do at work
🗺️
Lead a system design interviewClarify requirements, estimate, propose, deep-dive: the complete method.
⚖️
Make and defend a decisionLay out the trade-offs, put numbers on them, convince a tech lead or a business leader.
🏗️
Build a real architectureCache, queues, replication, multi-region: knowing what to use, when, and why.
🚨
Stay calm during an incidentFollow the request, find the bottleneck, apply the right fix.
Access
Start for free, continue with your subscription
The first room is free. The rest of the maze comes with the Runbookly subscription, along with the Labs and the certifications.
Discovery
0 USD forever
- The complete first room, simulation included
- The full glossary, free to read
- Your progress saved
👑 The complete path
Intermediate
9 USD / 30 days
- All 30 rooms and the 5 bosses
- Smart reviews of your mistakes
- The Labs, the Studio and the Interview Room
- Certification prep, from One Nine to Five Nines
No commitment · cancel anytime
FAQ
Frequently asked questions
I am a complete beginner. Is this for me?
Yes. The first room starts from “what happens when I type an address?”. Every technical term is defined the moment it appears.
How much time per day?
A room takes 5 to 8 minutes. You choose your daily goal, from 1 to 5 rooms, and we gently remind you to keep your streak.
Does it prepare for interviews and certifications?
Each floor maps to a Runbookly certification, and floor 5 trains you to lead a real architecture discussion, as in an interview or a design review.
Is the course available in French?
Yes, the whole path exists in English and in French. Switch the site's language at any time, your progress follows you.
What happens after the first room?
You keep your progress and your milli-Uptime. To open the rest, a Runbookly subscription is all it takes, and it also unlocks the Labs and the certifications.