System Design Cheat Sheet

What's inside#

• A six-step method for approaching any system design
• Core qualities with precise definitions, plus an availability "nines" table of allowed downtime
• Back-of-the-envelope estimation: time and data-size conversions, formulas and a worked example
• Building blocks, from load balancers and CDNs to queues and search indexes
• Storage choices, replication and partitioning strategies
• Consistency models, CAP and PACELC, and SQL isolation levels
• Caching strategies, eviction and failure modes, and communication styles
• Reliability patterns, rate-limiting algorithms and observability
• A trade-off table and twelve questions to ask of any design

How to use it#

1. Keep it open while you design, review a design doc or prepare for an interview.
2. Follow the six-step method on page 2 to structure your thinking.
3. Use the estimation page to size the system before choosing components.
4. Finish with the review questions on the last page.

Limitations#

• It's a summary. Each topic deserves deeper reading before you depend on it in production.
• Estimation numbers are for orders of magnitude. Measure real systems before committing to capacity.
• Database behavior varies by engine and version; check your own database's documentation.

License

Free to use, share and adapt, including commercially, as long as you credit Letinix and link to this page. Licensed under CC BY 4.0.