01 security
How a database stores passwords safely The password never reaches the disk. A fingerprint does, and a random salt makes that fingerprint useless to anyone holding a precomputed table.
10 steps · live demo
02 frontend
How micro frontends work Microservice boundaries pushed all the way into the browser, so a team can own a slice of the product from database to pixel.
10 steps
03 storage
How S3 reaches eleven nines of durability Durability is not one clever trick. It is erasure coding, checksums at every hop, constant background auditing and a repair fleet sized against real failure rates.
12 steps
04 storage
How S3 is put together An object store built from many small services, cheap spinning disks, and a log-structured layout that turns random writes into sequential ones.
8 steps
05 routing
How Uber computes an ETA Shortest path on a road graph, made fast by precomputing inside partitions, and made accurate by snapping noisy GPS onto real roads first.
8 steps
06 databases
How YouTube scaled MySQL with Vitess Rather than leaving MySQL, they wrapped it: a proxy that shards and pools, and a sidecar that protects each instance from expensive queries.
8 steps
07 compute
How AWS Lambda runs your function Multi-tenant compute where the hard problems are isolation between strangers and the cold start you pay when no warm sandbox exists.
11 steps
08 payments
How Apple Pay keeps your card number out of it The phone never holds your card number and neither does Apple. It holds a device-specific token plus the ability to sign a one-time cryptogram.
9 steps
09 databases
How Figma scaled Postgres A decade of scaling in the order most teams should do it: bigger box, replicas, cache, split by domain, and only then shard rows.
8 steps
10 devices
How an AirTag gets found A battery-powered beacon with no GPS and no network, located by borrowing the radios of strangers’ phones — without those phones, or Apple, learning anything.
10 steps
11 payments
How Stripe stops a payment charging twice Networks time out mid-request and clients retry. Idempotency keys make the retry safe by letting the server recognise a request it has already completed.
10 steps
12 routing
How Uber finds drivers near you Proximity search on a moving fleet, solved by giving every point on Earth a cell id so "nearby" becomes a key lookup instead of a distance scan.
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13 caching
How Meta measures cache consistency At this scale invalidation races are inevitable, so the interesting engineering is in detecting stale entries rather than pretending they cannot happen.
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14 scale
How Tinder handles a billion swipes a day Geospatial search, a write-heavy stream of swipes, and a sharding problem created by the fact that the world wakes up in waves.
12 steps
15 networking
How a domain name becomes an IP address A hierarchy of caches and referrals: several lookups the first time, and usually none at all after that.
6 steps
16 security
How a JWT proves who you are A signed claim the client carries, so the server can trust it without looking anything up — which is the whole benefit and the whole problem.
12 steps