System design interview question
"Design a transactional system — say ride bookings or order placement — that keeps working when infrastructure fails. A database node dies, a whole availability zone goes dark, or an entire region becomes unreachable. Tell me what happens to in-flight transactions in each case, and what your recovery time and data loss look like."
failure-domain reasoning and the RPO/RTO trade-off — explicitly, with numbers. Most candidates can say "we have replicas". The signal is whether they can state how much data you lose and how long you are down for each failure class, and whether they understand that synchronous replication buys durability with latency and availability.
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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