System design interview question
"Design a notification system. Any service in the company can call it to notify a user via push, SMS, email, or in-app. It must handle 10 billion notifications a day, respect user preferences, never spam, and never lose a critical notification like a two-factor code."
reliable delivery through unreliable third parties, plus the product-facing concerns that separate a toy from a platform: preferences, deduplication, rate limiting, templating, and priority. It is one of the most frequently asked questions in the industry because it is a genuine platform-engineering problem and it is hard to fake.
On Practick another engineer interviews you live for 60 minutes on a question from this bank. They have the full interviewer guide beside the call: the answers to your clarifying questions, the numbers to hand out, a ladder of follow-ups and a scoring rubric. You get the model solution once the session settles. It is free: interview someone for an hour and you have earned your own.
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