01
Design the Serving Infrastructure for an LLM-Powered Feature
Practice
- capacity estimation
- GPU economics
- continuous batching
- autoscaling signals
- latency vs. throughput
- token streaming
Core Practice Edition · Vol. 1
System design interviews are won on reps, not reading.
A practice-first workbook for SDE-2 / SDE-3 engineers. Five complete interview simulations, stop gates that make you commit before you read, and a 32-point self-grading rubric.
127-page professionally designed PDF · Instant download · Lifetime updates to Vol. 1
Stop gate
Do not read further until you have written your capacity estimate — request rate, GPU count, and cost per hour. The answer on the next page is worthless if you haven't committed to yours.
SELF-GRADE · 8 DIMENSIONS × 0–4
requirements · capacity · architecture
deep dives · tradeoffs · failure modes …
requirements · capacity · architecture
deep dives · tradeoffs · failure modes …
26
/ 32 · SDE-3
The mechanics that make this a workbook, not a book.
5
interview simulations
12
structured sections per problem
32
point self-grading rubric
127
page professional PDF
New · Volume 2
Correctness Under Uncertainty.
The advanced companion to Volume 1: five interviews where the obvious answer breaks — retries, stale authorization, deletion, decision stability, and contention. A 251-page workbook with 50 diagrams and the D1–D8 self-grading rubric.
- 5 advanced interview simulations
- Agentic execution, retrieval, deletion, payment risk, ticketing
- 16-section arc · Stop Gate at §9 · interviewer challenges
- 251-page PDF · 50 diagrams · 32-point D1–D8 rubric
Free sample · no risk
Try the interview before you buy the workbook.
Not sure it's for you? Download the free 12-page preview and attempt the opening stages of a real Practice System Design simulation — actual workbook pages, not a brochure. It stops right before the reference solution: you get the exercise; the full analysis, benchmark solution, and remaining four problems are in Volume 1.
What's inside the free sample
- The Practice Loop and the 10-step workflow
- The 12-section chapter structure and readiness benchmarks
- All five interview problems, listed
- A real LLM-serving interview: prompt, clarification, requirements, capacity estimation
- The Stop Gate — commit your design before the solution
The problem
Reading about system design isn't the same as practicing it.
Most prep material lets you nod along to someone else's answer. In the interview, nodding isn't available. This workbook is built around three mechanics that force real practice.
01 / STOP GATES
Work before you read
At every decision point the book stops you: write your requirements, commit to your capacity math, sketch your architecture. Only then do you compare against the reference solution. No passive scrolling.
02 / DECOY QUESTIONS
Learn to smell the trap
Interviewers probe with plausible-sounding but wrong directions. Each problem includes decoy questions that train you to recognize when a follow-up is testing your judgment, not your memory.
03 / SELF-GRADING
Know where you stand
Score every attempt across 8 dimensions on a 0–4 scale, then read your total against the workbook's SDE-2 and SDE-3 practice-readiness benchmarks — before a real interviewer does.
The method
The Practice Loop
Every problem in Volume 1 runs the same eight steps, in the same order. The sequence is the product: it is what turns an hour of reading into an hour of interview reps.
- 01PromptAn intentionally underspecified question, as asked
- 02ClarifyResolve ambiguity before you design anything
- 03EstimateCapacity math you can defend out loud
- 04DesignCommit to an architecture on paper
- 05DefendInterviewer challenges and decoy questions
- 06Stop GateNo reading ahead until your answer is written
- 07CompareReference solution and trade-off tables
- 08GradeScore the attempt on all 32 points
Attempt→Commit→Defend→Compare→Grade→Repeat
See what you're actually getting
This is what practice looks like.
Real spreads from Volume 1, not mockups. Click any page to read it full size.
Inside Vol. 1
Five interview simulations.
Modern AI infrastructure alongside the distributed-systems classics. Each problem runs the full 12-section arc — requirements, capacity math, architecture, deep dives, trade-off tables, a reference diagram, and grading.
02
Design Twitter Feed + Personalized AI “Catch Me Up” Recap
Practice
- fan-out on write vs. read
- timeline caching
- async pipelines
- critical-path isolation
- cost per recap
- graceful degradation
03
Design a Distributed Rate Limiter
Practice
- token bucket vs. sliding window
- atomic check-and-consume
- fail open vs. fail closed
- clock skew
- hot keys
- RateLimit headers
04
Design a Distributed Job Scheduler / Delayed Task Queue
Practice
- claim vs. execution leases
- exactly-once illusions
- idempotent handlers
- SKIP LOCKED semantics
- retry & backoff
- failure modes
05
Design a Real-Time Collaborative Document Editor
Practice
- OT vs. CRDT
- merge semantics
- state-vector reconnection
- presence at scale
- persistence & snapshots
- websocket fan-out
SELF-GRADE · PROBLEM 030–4 PER DIMENSION
Requirements
Capacity math
Architecture
Deep dives
Tradeoffs
+ 3 more dimensions
SDE-2 practice-ready → 20 / 32
SDE-3 practice-ready → 26 / 32
Honest scoring
A rubric that tells you where your design breaks down.
- 8 dimensions, scored 0–4. Built around the dimensions commonly evaluated in system-design interviews — not a vague "did you mention caching" checklist.
- Practice-readiness benchmarks. 20+/32 is the workbook's SDE-2 practice-readiness benchmark and 26+/32 its SDE-3 practice-readiness benchmark. They are practice targets for tracking your own progress, not company hiring standards.
- Regrade on every rep. Problems are built to be re-attempted, so the same score sheet shows movement across passes instead of a one-time verdict.
Honest fit
This workbook is not for everyone.
Built for you if
- You already understand core distributed systems concepts — load balancers, caches, queues, replication
- You're preparing for SDE-2 / SDE-3 (or equivalent) interview loops
- You want realistic practice rather than passive reading
- You want to find your weak spots through self-grading, not reassurance
Skip it if
- You're completely new to backend or system design
- You only want short interview answers to memorize
- You're looking for a beginner theory textbook or a reference encyclopedia
- You're interviewing for roles without a system design round
Two volumes
Choose your volume.
New to this? Start with Volume 1 — it builds the practice method on foundational problems. Ready for correctness under uncertainty? Volume 2 is the advanced set. Or get both and save.
Volume 1 · Foundational
System Design Interview Workbook
$19
one-time purchase
- 127-page professionally designed PDF
- 5 foundational interview simulations
- LLM serving, feed, rate limiter, scheduler, editor
- Stop gates, reference solutions, 32-point rubric
- SDE-2 / SDE-3 practice-readiness benchmarks
- Lifetime updates to Volume 1
Secure checkout via Gumroad · 7-day refund window · eligibility applies
Prices in USD. Currency conversion and applicable taxes are shown at checkout.
New
Volume 2 · Advanced
Correctness Under Uncertainty
$29
one-time purchase
- 251-page professionally designed PDF
- 5 advanced interview simulations
- Agentic execution, retrieval, deletion, payment risk, ticketing
- 50 diagrams · 32-point D1–D8 rubric
- Stop gate at §9 · interviewer challenges
- Lifetime updates to Volume 2
See the full Volume 2 page
FAQ
Questions, answered.
What format do I get?
A 127-page professionally designed PDF, built for reading, printing and annotating. It works offline once downloaded, on any device that opens a PDF.
What level is it pitched at?
Mid-level to senior engineers preparing for SDE-2 / SDE-3 loops and equivalents. You should already know what a load balancer, cache and message queue are — the workbook trains you to assemble and defend designs under interview conditions.
Should I buy it if I am new to system design?
No. It assumes working knowledge of core distributed systems building blocks and offers no beginner theory chapters. Learn the fundamentals first, then use this to practise.
What is inside Volume 1?
Five complete interview simulations, each running the same 12-section arc: prompt, clarification, capacity estimation, architecture, deep dives, interviewer challenges, stop gates, trade-off tables, a reference architecture, and self-grading against the 32-point rubric.
How is the 32-point rubric meant to be used?
It is a self-grading framework built around dimensions commonly evaluated in system-design interviews: eight dimensions scored 0–4. Use 20+/32 as the workbook's SDE-2 practice-readiness benchmark and 26+/32 as its SDE-3 practice-readiness benchmark. They are practice benchmarks, not official company hiring standards.
How are the files delivered?
Checkout is handled by Gumroad. After payment you get an immediate download link for the PDF, plus an emailed receipt with permanent access to the same file.
Do I get updates?
Yes. Every revision of Volume 1 is free for buyers. Volume 2 is available separately or as part of the two-volume bundle.
Are the numbers current?
Capacity math uses 2026-calibrated assumptions — GPU throughput and pricing ranges, current header standards, modern infrastructure patterns — and each chapter states the assumptions it reasons from rather than presenting one number as universal.
Can I get a refund?
Refund requests may be submitted within 7 days; eligibility conditions apply. Because this is a digital product, refunds are intended for accidental duplicate purchases, technical issues preventing access to the files, or if the workbook materially differs from its description. Email contact@practicesystemdesign.com with your order details. See the Refund Policy for full details.
The whole idea
You don't need another system design answer to read. You need another problem to solve.
Set the timer. Clarify the problem. Estimate the load. Draw the architecture. Defend the trade-offs. Then stop, commit, and grade yourself — five times over. That's the rep this workbook is built to give you.