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Module Quiz

Complete this quiz after finishing all concept and practice pages. Save your answers before opening separate quiz calibration.

Current Module Questions​

Question 1: Requirements Discipline​

You are asked to "design a notifications service." What are the first three things you must explicitly ask before any design?

Question 2: Estimation Drill -- Feed Writes​

A service has 100 M DAU; each user writes 5 items per day; each item is 500 bytes. Estimate (a) writes per second average, (b) raw storage per day, (c) raw storage per year.

Question 3: Estimation Drill -- Cache Sizing​

Your read workload is 80/20 skewed. You want 95% cache hit rate on the last 24 hours of content, where 24 hours = 1 TB raw of items. Roughly how much cache memory do you need?

Question 4: Estimation Drill -- Latency Budget​

P99 target 200 ms. Client to edge: ~30 ms. Cross-continent round trip: ~150 ms. How many cross-continent round trips can the request path afford?

Question 5: Pick the Tradeoff -- Storage​

You are designing a time-series metrics pipeline, 1 M data points per second, 100 B each, with mostly-append writes and aggregate reads over recent windows. What storage would you choose and what would you reject?

Question 6: Pick the Tradeoff -- Consistency Model​

Two users race to reserve the last seat on a flight. What concurrency mechanism do you pick, what do you reject, and why?

Question 7: Partitioning Key​

A social feed stores one row per (user, post) in a user_timeline table. Should you partition by user_id or by author_id? Why?

Question 8: Cache Placement Critique​

A junior engineer proposes putting a cache in front of a billing ledger to "speed up reads". Why is this a correctness risk, and under what condition could it be acceptable?

Question 9: Bottleneck vs SPOF​

A centralized ID-generation service runs on a single instance. It serves 5 K QPS at 10% CPU. Is it a bottleneck? Is it a SPOF? What do you do?

Question 10: 10x Scale Reasoning​

Your system handles 10 K QPS today with a single Redis cache (50 GB RAM, 80% hit rate). At 10× traffic (100 K QPS, same workload shape), what breaks first and what do you change?

Question 11: Failure Walk -- AZ Outage​

Your feed service has app servers and a cache in every AZ of one region, plus a primary DB in AZ-1 with a synchronous replica in AZ-2. AZ-1 goes dark. What happens, and what is your RTO/RPO?

Question 12: Pick the Tradeoff -- Fan-out​

For a chat app with groups of 1-100,000 members, compare "fan-out on write to every recipient's mailbox" vs "fan-out on read by joining on the group". Which do you pick for which group sizes?

Question 13: Trade-off Articulation​

Write a single-sentence trade-off statement in the form "I chose A over B because C, accepting cost D" for the decision "use cache-aside with explicit invalidation".

Question 14: Four-Phase Discipline​

You are 22 minutes into a 45-minute interview and still in phase 2 (high-level diagram). What do you do?

Question 15: Design Doc Minimum​

Name three sections of a design doc that, if missing, cause a senior reviewer to reject the doc.

Interleaved Review Questions​

Prior Module Question 1 (S7 Architecture & DDD)​

Why is a bounded context a design tool rather than just a naming convention?

Prior Module Question 2 (S7 API Design)​

What is the difference between an API's contract and its implementation, and which one are consumers coupled to?

Prior Module Question 3 (S6 Distributed Systems)​

State the CAP theorem in one sentence and name which property modern systems typically preserve during a network partition.

Prior Module Question 4 (S6 Databases)​

Why is a secondary index on a write-heavy table expensive, and what is the typical diagnostic when indexes are overused?

Prior Module Question 5 (S7 Architecture)​

What is the difference between a quality attribute (architecture characteristic) and a functional requirement, and why do architects pay more attention to the former?

Self-Assessment and Remediation​

Mastery Level (90-100% correct):

  • Retrieval is strong; complete all module and semester evidence gates before advancing.

Proficient Level (75-89% correct):

  • Review only the missed concept pages and redo the associated mini drills.
  • Particularly re-run any missed estimation question with pencil and paper until fluent.

Developing Level (60-74% correct):

  • Rework practice pages 1 and 3 (estimation/framing, stress test).
  • Run at least two of the four design katas again with a timer.
  • Revisit Cluster 3 and Cluster 4 concepts with attention to the mini drills.

Insufficient Level (<60% correct):

  • Return to the concept sequence and rebuild the method in order.
  • You likely cannot yet estimate, deep-dive, or stress-test a new system without reference; this is the first thing to fix.
  • Before advancing, pass a timed 45-minute mock with a peer where you hit all four phases.

Progression boundary​

Quiz performance calibrates retrieval and reasoning. It does not replace runnable work, changed-case transfer, the module assessment or required semester evidence. Consult practice calibration for the additional independent cases.