Imagined it a hundred times? Watch it once.

how many servers?

Every box on that sketch has its own page.

Load balancing, caching, sharding, rate limiting. Each idea gets one short page with a figure, and the ones that are hard to picture run live, so you stop guessing how they behave.

119 system design73 classes and patterns44 algorithms

ok, but where do I start??

Nothing shows up before you're ready for it.

A learning path puts every page in order. Each step uses only what came before it, and a real problem arrives after the first few ideas, then keeps coming.

1. 8Load balancingconcept
2. 10Caching strategiesconcept
3. 29Message queues & pub/subconcept
4. URL Shortenerproblem
5. Rate Limiterproblem
6. Distributed cacheplanned
7. 86The circuit breaker patternconcept

A few of the 154 steps on the system design path, with their step numbers.

will this hold at peak??

Press play on the whole thing.

Every dot is a request, 12,400 of them a second, moving through the parts you just learned. Pause it whenever you like, and walk through it one step at a time until every arrow makes sense.

what if cards are slow?

Then break it on purpose.

The card network drags to 3,000 ms. Payments pile up, errors climb, the gateway turns red. Then the circuit breaker pattern from step 86 trips, and bookings keep moving while payments wait their turn.

but what does the code look like?

Then get down to the classes.

Six classes park a car and charge for it. This is Hilltop Garage, step 19 of the low-level design path. Polymorphism and the strategy pattern each get a page before it, with code in Java, C++, Python and JavaScript, and then you design the garage yourself in Java or TypeScript.

and how does it pick a spot?

And down to every line.

The garage's findSpot() checks spot after spot. Keep the free spots sorted by size and a binary search finds the first one that fits in 4 looks instead of up to 14, or 11 instead of 2,000 on a big level. That's Linear & binary search, step 18 of the algorithms path.

ok, I'm in.

Stop imagining. Pick a path.

One idea at a time, with real problems along the way, and the ones still being built marked as planned.

• System designFrom one server to a platform for millions154 steps
• Low-level designClasses, patterns and the code inside a service85 steps
• AlgorithmsFrom arrays to graphs, one topic at a time79 steps