Interview walkthrough — design a data platform end-to-end

At a glance

Learning objectives

• Run a 45-minute design walkthrough with a repeatable time-boxed shape
• Support each design claim with a citation from the five source references
• Close an answer with a deployed precedent instead of a shrug

What you need

• Lessons 1–8 (this walkthrough composes them)
• A timer and a whiteboard or shared doc

Steps

1. Start from the exercise format — worked design exercises are one of the Primer's three pillars, and every one of them opens with requirements and estimates before architecture, so rehearse that order until it is reflexive. (from ref-system-design-primer )
2. Use the path's own vocabulary — the Primer is the standard on-ramp for the estimation and tradeoff vocabulary this stage's interview path needs, which means the words you drilled in lessons 2 and 4 are the ones the interviewer expects to hear. (from ref-system-design-primer )
3. Structure the answer on the canonical axes — DDIA's six words (reliability, scalability, replication, partitioning, consistency, batch/stream) are called the single highest-value read for system-design interviews, so let the deep dive be a mechanism, not a product tour. (from ref-ddia )
4. Let the deep dive ride the mechanisms — replication, partitioning, and consistency are the DDIA chapters your data platform touches first, so spend the middle minutes on the hot table's partition layout and merge semantics rather than on logos. (from ref-ddia )
5. Close with evidence — reference architectures are the closest thing to citable evidence when an answer needs a real-world precedent, so end the walkthrough by pointing at a deployed architecture that ships your shape. (from ref-aws-arch-center )
6. Pick a precedent that matches the domain — the AWS collection's Well-Architected pillars and serverless data lake patterns are concrete vendor material for grounding sizing and tradeoff arguments, which is exactly what the last five minutes of an interview need. (from ref-aws-arch-center )

Check yourself

• You can deliver the 45-minute shape — requirements, numbers, architecture, deep dive, reliability, precedent — inside the time box, twice, on different prompts.
• Every claim in your answer traces to one of the five references — nothing stands on vibes.

Worked example

45-minute data platform design — the shape:
  0-5   Requirements: functional + non-functional (freshness, volume, growth)
  5-10  Back-of-envelope: QPS, storage/day, retention, peak factor
  10-20 Architecture: ingest -> raw -> process -> serve; name each store
  20-30 Deep dive: partitioning + replication for the hot table;
        consistency semantics for the merge
  30-40 Reliability: SLIs/SLOs, error budget, failure modes, backfill story
  40-45 Precedent: point at a reference architecture that ships this shape

Sourced from

• The System Design Primer
• Designing Data-Intensive Applications (O'Reilly)
• AWS Architecture Center

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Common gotchas

• Jumping to architecture before the numbers is the most common interview failure — requirements and estimates buy the right to draw.
• A deep dive on brand names instead of mechanisms collapses under the first 'why'.
• Ending without a precedent leaves the interviewer holding an untested idea instead of a checked one.

Production considerations

• Rehearse the walkthrough against a real platform decision, not a toy prompt — the vocabulary transfers.
• Keep the five references bookmarked; citing the source of a claim is itself a signal.

Diagram

45-minute data platform design
   |
   |- 0-5   requirements   --> functional + non-functional (freshness, volume)
   |- 5-10  estimation     --> QPS, storage/day, retention, peak factor
   |- 10-20 architecture   --> ingest -> raw -> process -> serve; name storage
   |- 20-30 deep dive      --> partitioning + replication on the hot table;
   |                          consistency for the merge
   |- 30-40 reliability    --> SLIs/SLOs, error budget, failure modes, backfill
   |- 40-45 precedent      --> one reference architecture that ships this shape
   |
    --> every claim cites one of the five sources

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