Start with HLD
Map users, services, data ownership, communication, scale, and failure boundaries.
System Design
5 chapters · 17 challenges · The Scale Foundry
Understand the idea, practise through play, then prove it in code. Choose your next quest below.
Visual introduction to this topic
Start here · 3 minute mental model
What is system design?
System design turns product requirements and scale into a system you can build and operate. HLD maps services, data, communication, and trust boundaries; LLD zooms into one component's APIs, objects, state transitions, invariants, and concurrency rules.
Think of launching an online game. A button press crosses devices, networks, servers, and storage. The design decides who owns truth, what can fail, and how players recover.
Follow one real request end to end, then inspect scale and every failure boundary.
Zoom into LLD
Define contracts, objects, schemas, states, invariants, concurrency, errors, and tests.
Prove production readiness
Review reliability, security, performance, cost, deployment, observability, and recovery.
What you will learn firstThe Two Design Lenses
Begin the guided lesson See one system from architecture down to code
01
System Design Foundations
0/5 completeLearn HLD, LLD, requirements, architecture boundaries, component contracts, and production readiness.
01
easy
The Two Design Lenses
See one system from architecture down to code
+160 XP
02
easy
The Requirements Compass
Turn a vague product into measurable design targets
+170 XP
03
easy
Draw the High-Level Map
Place boundaries, ownership, and communication with intent
+180 XP
04
medium
Open the Low-Level Workshop
Turn one service promise into contracts and invariants
+190 XP
05
medium
The Production Readiness Gate
Review reliability, security, operations, and cost before launch
+200 XP
02
Frame the Interview
0/3 completeTurn ambiguity into requirements, estimates, contracts, and access patterns.
03
Scale the Core
0/4 completeUse caches, streams, partitions, and explicit consistency to grow safely.
09
medium
Feed Cache Frontier
Accelerate reads without serving stale chaos
+240 XP
10
medium
Notification Switchyard
Decouple delivery while controlling duplicates
+250 XP
11
hard
Metric Shard Atlas
Partition writes without creating a hot key
+260 XP
12
hard
Replica Compass
Choose consistency from the invariant
+270 XP
04
Make It Dependable
0/3 completeDefend reliability, security, and observability under real failure.
05
Architecture Interviews
0/2 completeCombine every tradeoff in full autocomplete and global video case studies.
Source reviewed
Built from authoritative material
This track is checked against the sources below. Visual traces still carry their own complete or guided coverage label, so unfinished explanations are not presented as complete executions.