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System Design 101

You know how to build a feature. Now see how requests, data, traffic and failures shape the whole system.

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Nine short lessons. Start with one web request and build toward distributed system trade-offs.

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Follow one request from the browser to the database and back.

Turn users and traffic into the rough numbers a design needs.

Spread traffic across servers and survive a machine going down.

Keep hot data close and stop repeated reads from melting the DB.

Move static content closer to users and away from your origin.

Use copies of data for read scale and failover.

Move slow work off the request path and absorb traffic spikes.

Choose what stays correct and what stays available during failure.

Split data only when one machine is no longer enough.