Pick a module, any module
Core Concepts
Scalability, availability, CAP theorem, and the vocabulary everything else builds on.
9 lessonsNetworking Fundamentals
OSI model, DNS, HTTP, TCP vs UDP, and load balancing.
8 lessonsAPI Fundamentals
REST vs GraphQL, WebSockets, webhooks, idempotency, and rate limiting.
8 lessonsDatabase Fundamentals
ACID, indexes, sharding, replication, and SQL vs NoSQL.
9 lessonsCaching Fundamentals
Caching strategies, eviction policies, distributed caches, and CDNs.
5 lessonsAsynchronous Communication
Pub/sub, message queues, and change data capture.
3 lessonsDistributed Systems & Microservices
Heartbeats, consensus, distributed locks, circuit breakers, and tracing.
8 lessonsArchitectural Patterns
Client-server, microservices, serverless, event-driven, and peer-to-peer.
5 lessonsSystem Design Tradeoffs
Ten head-to-head decisions you’ll be asked to justify in interviews.
10 lessonsInterview Practice
A framework for any prompt, plus easy, medium, and hard practice problems.
18 lessonsBuilt to actually stick
A few things beyond plain text, built where they genuinely help.
Diagrams that show the mechanism
Core Concepts lessons pair their explanation with a branded, animated diagram of the actual flow — not a decorative box-and-arrow filler.
Progress that stays on your device
Mark lessons complete and pick up where you left off. Tracked in your browser only — nothing is ever sent anywhere.
From the blog
Short, focused explainers — the concepts people search for most.
SQL vs NoSQL: How to Choose
The real tradeoff, not just "NoSQL scales better."
REST vs GraphQL: Which Should You Use?
Free HTTP caching vs. exactly the fields the client asks for.
What Is the CAP Theorem?
What it actually forces you to decide, and when.
Horizontal vs Vertical Scaling Explained
How to actually decide, and why most systems do both.
Load Balancing: Layer 4 vs Layer 7
L7 isn't only about HTTP — here's what that means.
How to Answer a System Design Interview
A repeatable six-step framework, not a memorized diagram.
TCP vs UDP: What's the Difference?
Why a late packet can be worse than a lost one.
Database Sharding Explained
Range vs. hash keys, and what cross-shard queries cost you.
Strong vs Eventual Consistency Explained
Fast ack now, or wait for every replica to agree?
Stateful vs Stateless Design Explained
Statelessness doesn't erase state — it just moves it.
ACID Transactions Explained
Four separately-breakable guarantees, not one blob.
What Is a CDN? A Simple Explanation
Caching distance itself, not just work.
Rate Limiting: Token Bucket & More
Why token bucket beats a naive fixed window.
The Circuit Breaker Pattern Explained
Fail fast instead of piling up timeouts on a dying service.
Sync vs Async Communication Explained
The one question behind nearly every comms tradeoff here.
Ready to stop dreading the interview?
Start with Core Concepts — everything else in the course builds on it.
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