Amazon DynamoDB
maang.io System Design Series
DynamoDB is AWS's fully-managed, serverless database from the Dynamo lineage — the same distribution ideas as Cassandra, but operated for you. Master its partition/sort keys, GSIs vs LSIs, capacity modes, tunable consistency, and query-first single-table design, and you can reason about planet-scale key-value systems and defend when to reach for it over a self-managed cluster.
This deep dive comes in four parts:
- Foundations & Core Concepts — the data model, keys, and partitions.
- Internals — capacity (RCU/WCU), adaptive capacity, indexes, and consistency, with worked numbers.
- Advanced Internals — Streams, TTL, and single-table design patterns.
- Interview — Staff/Principal Q&A: modeling, hot partitions, and DynamoDB vs Cassandra.
Amazon DynamoDB — Part 4: System Design & Interview Mastery
maang.io System Design Series
What is this?
You now know DynamoDB from the request router down to the WAL. This chapter is where that knowledge earns the offer. An interviewer doesn't want you to recite "DynamoDB uses Paxos per partition" — they want to watch you reach for it at the right moment, model the data query-first, and defend the trade-offs when they push back, especially against its cousin Cassandra.
Back to the warehouse one last time: the concierge, the aisles chosen by your box's label, the three buildings, the aisle foreman who authorizes every change. We'll first see where DynamoDB fits in real designs (with a full single-table model), then run a mock interview — for each question: what they're really asking, a model answer, and the senior line that signals you've done this for real.
The one-line idea: interviewers use DynamoDB to test whether you can match a datastore's shape to a workload's shape — high-throughput, key-accessed, always-on, on AWS — and then model query-first and live honestly with the costs (no joins, no ad-hoc queries, and you must know your access patterns before you design the keys).
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