System Design Fundamentals

A from-first-principles guide to system design — requirements and estimation, scaling, the data layer, and the distributed-systems building blocks that show up in almost every real architecture.

4 chapters · 12 sections · 23 min read · Updated Sep 12, 2026

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What you'll learn

How to turn an ambiguous prompt into concrete functional and non-functional requirements
How to do back-of-the-envelope estimation before committing to an architecture
When to scale vertically versus horizontally, and how load balancing actually works
How to choose between SQL and NoSQL, and how replication and sharding scale a database
The CAP theorem and what it really constrains during a network partition
The distributed-systems building blocks — queues, CDNs, circuit breakers — behind most real architectures

Chapters

1. Foundations
System design is often taught as a grab-bag of buzzwords — "just add a cache," "shard the database," "put a queue in front of it." This cha…
3 sections
2. Scaling Fundamentals
Once you know what the system needs to do and roughly how much load it's under, the next question is almost always: what happens when one m…
3 sections
3. The Data Layer
Most system design decisions eventually come back to the database, because it's usually the hardest part of a system to scale after the fac…
3 sections
4. Distributed Systems Building Blocks
The last three building blocks that show up in almost every real distributed system: decoupling work with queues, pushing content physicall…
3 sections