Design a Distributed Key-Value Store

"Design a distributed key-value store" is the storage prompt Amazon reaches for most, and it lands harder in an Amazon room than anywhere else, because it is Dynamo. The internal paper Amazon published in 2007 is the direct ancestor of DynamoDB. It was born to solve one Amazon problem: a shopping cart that accepts a write even with a data center on fire. Hand a candidate this prompt and you are asking them to reverse-engineer a system the company invented, so the room knows the source material. The store does two things, get(key) and put(key, value), and nothing else. No joins, no secondary indexes, no transactions across keys. Every hard decision falls out of taking that tiny interface and making it survive at scale.

One property defines this design, and it is availability. Amazon decided that for a service like the cart, being able to write is worth more than every reader seeing the freshest value the instant it is written. A customer adding an item must succeed even when nodes are down, networks are split, and replicas disagree. That is a deliberate trade: the system stays writable and reconciles disagreements afterward, rather than refusing writes to stay perfectly consistent. Reach for that trade on purpose, and name what it costs, and you've found what the prompt is really about. Raw throughput is the decoy; the real exercise is surviving partial failure without ever turning a writer away.

The Amazon angle

This prompt carries extra weight at Amazon because it is Amazon's own paper. The interviewer may have read the Dynamo paper, may have worked on DynamoDB, and will know exactly where you are hand-waving. So choose availability over consistency and tie it to the product: the cart must always accept the write, because a failed add-to-cart drops the customer out of checkout and costs the sale. That trade is Customer Obsession expressed as architecture, the Leadership Principle Amazon calls its north star, and Amazon grades all sixteen principles inside the design round rather than in a separate slot. Expect them to Dive Deep on the quorum math too.