← All learning pathsLearning path
Beginner~85 min·5 systems· All freeFree Starters
All five free systems in one path: warm-up shortener and IDs, then feed, chat, and messaging. No paywall mid-path.
After this path you will be able to
Complete a full free arc: generate keys, cache reads, fan out a feed, and reason about realtime delivery, then decide what Pro depth you want next.
Interview approach for this path
- 1.Open with requirements and scale before drawing boxes.
- 2.Name the free patterns you practiced: cache-aside, fan-out, persistent connections.
- 3.Call out one failure mode per system (cache miss stampede, queue backlog, reconnect storms).
- 4.Close by saying what you'd add with Pro depth (CDN tiers, geo dispatch, payment ledgers).
Systems in this path
5 total1
URL ShortenerBeginner·12 min
Hashing, key generation, read-heavy caching.
2
Unique ID Generator (Snowflake)Beginner·12 min
64-bit time-sortable IDs: timestamp + worker id + sequence, minted locally with no per-request coordination.
3
Instagram FeedIntermediate·18 min
Fan-out on write vs read, ranking, CDN.
4
Chat (Slack-style)Intermediate·18 min
Room-based pub/sub fanout across gateway instances.
5
Persistent connections, message queues, delivery.
Concepts reinforced throughout