4. Design a Notification System
Deliver email, push and SMS with preferences, retries and honest delivery status.
ClassicMedium
Guided practice
Start with a template. Work through each step. Ask Coach when you need a second opinion.
All designs 8
Ordered by design numberCompany tags are community-reported. Counts on cards show how many people reported that design.
QueuesClear filters
8. Design a Video Streaming Platform
Turn uploads into playable renditions and serve viewers through unreliable networks.
ClassicHard30. Transactional Outbox
A service commits to its database and then publishes an event. If it dies in between, the row exists and no one hears about it. Publishing first has the mirror problem: an event for a write that never happened. There is no ordering of two independent systems that makes this safe.
Product & backendMedium39. Design a Calendar System
Google Calendar-style events with recurrence, RSVPs and on-time reminders, using CDC for change notifications and a delay queue for reminders.
ClassicMedium47. Design an Online Judge like LeetCode
Run strangers' code safely in single-use microVMs, return verdicts within 5 seconds, and rank 100,000 contestants live.
ClassicMedium53. Design a Stock Trading App like Robinhood
Live prices to five million phones through per-symbol pub/sub, and market and limit orders over FIX that are never lost, sent twice or overspent.
ClassicMedium89. Design a Donations Website for a Charity Event
Ten charities, three days, $100 M: charge through a third-party processor exactly once, queue the broadcast spikes, keep live totals on sharded counters. One-hour boards for junior, senior and staff, with the theory behind them.
ClassicMedium101. Design a Webhook Delivery System
Signed HTTPS callbacks for a billion events a day, at least once, retried for three days, with no endpoint able to slow another.
ClassicMedium