A design review tests assumptions by tracing ordinary requests and failures. It exposes gaps hidden by a diagram’s happy path.
Before you start
You should understand API requests, storage and basic capacity estimates. Begin with a concrete user action and its correctness requirement. Draw data flow and failure boundaries before selecting infrastructure; a technology name by itself does not explain why a design meets the requirement.
The practical goal is to reason through this situation: Follow a timed-out write and ask how a client discovers whether it committed. Read the walkthrough first, then try the interview exercise before opening its answer. The important part is explaining the decision and its consequences, rather than remembering a definition alone.
Step-by-step walkthrough
Step 1: Trace ordinary read and write
Identify data ownership and response meaning at each boundary.
Step 2: Inject uncertainty
Ask what happens when a write commits but its response disappears.
Step 3: Test overload and recovery
Every queue or dependency needs bounds and observable outcomes.
Worked scenario
Follow a timed-out write and ask how a client discovers whether it committed.
A diagram shows client, API and database, but does not explain whether a timed-out creation should be retried. Following that request reveals the need for stable operation identity and outcome retrieval. Repeat the exercise for overload and dependency failure to expose assumptions invisible in component boxes.
Common mistake
A component diagram without ownership or recovery rules leaves critical behavior undefined.
Verify the behavior
Review one read, write, timeout and recovery using explicit observable results.
Interview exercise
Review a proposed architecture.
Answer and reasoning
Trace one read, one write, one overload and one dependency failure, identifying data ownership and observable outcomes.
Continue learning
Compare the scenario with the System Design interview questions and test your understanding with the System Design MCQs. For terminology and implementation details, consult the reference material.