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System Design, Intermediate
You know the building blocks. Now learn how they behave under real load: load balancing algorithms, CDNs, queues, and consistency tradeoffs.
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Load balancing in depth
22 min read
The order I'd read them in
About 4 h 16 min of reading. Tick off what you've read, it is remembered on this device.
- Load balancing in depthThe box everyone draws and nobody explains — where L7 earns its latency, why consistent hashing keeps recurring, and how a health check turns a brownout into an outage.
- CDNsMove the bytes closer to the user — the cheapest 10x in system design, right up to the moment you cache something personal.
- Message queues & async processingThe request path should only do the work the user is actually waiting for — everything else goes on a queue and gets retried.
- Consistency modelsEvery consistency model is just a rule about which stale reads you are willing to let a user see.
- ReplicationKeeping copies of the same data on several machines is easy until the machines disagree, and then every design choice is a decision about which copy you are willing to lose.
- Rate limiting & throttlingThe only thing standing between one badly-behaved client and everybody else's latency.
- Designing for availabilityAvailability multiplies down your dependency chain — five nines in one box is four nines in a system.
- Storage systemsBlock, file, object — and why the bytes of a user upload should never touch your app servers.
- Search systems (surface)The database scans; the inverted index looks up. Everything else in search is ranking and staleness.
- Microservices and service discoveryWhen splitting a system pays for itself, what it costs, and how one service finds another once the addresses keep changing.
- Security basics for designWho is calling, what may they do, and what happens on the day a secret leaks.
- Walkthrough: a news feed / chat appFan-out on write, fan-out on read, and the hybrid that exists because one account has 150 million followers.
- Walkthrough: a notification systemA notification system looks like a loop over users and a call to an API, until you remember that the APIs are other people's, the users can say no, and a retry can wake someone up twice.
Practice at this level
No exercises tagged for this level yet. The ones on each chapter above still work.