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.
Classic designs 7
Ordered by design numberCompany tags are community-reported. Counts on cards show how many people reported that design.
Amazon SQSClear filters
45. Design a Job Scheduler
Run 10,000 jobs a second within two seconds of their time, at least once, with retries, fairness between tenants and exactly-once effects.
ClassicMedium46. Design a Web Crawler
Ten billion pages in five days, politely, without losing progress: fetchers and parsers, domain locks, bandwidth math, deduplication and a crawl that stays fresh. One-hour boards for junior, senior and staff.
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.
ClassicMedium69. Design Long-Running Tasks: Async Jobs with Progress and Results
Accept in milliseconds, work in the background: leases and heartbeats, retries and dead letters, progress by SSE and webhooks, fairness across tenants.
ClassicMedium80. Design a Message Queue like Amazon SQS
Build a queue around visibility leases and explicit acknowledgement, then add replicated partitions, FIFO groups, tenant fairness and bounded redrive: three self-contained interview boards.
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