Lesson 110 — Advanced

Capstone: AI System Design Document

Capstone: poore L9 ko ek interview-ready design document mein likhna. Ek system chuno, requirement sheet se lekar failure matrix, caching plan aur trade-offs tak sab sections bharo — har box ke saath why, rejected alternative aur measurement plan.

⏱ 10 min• Advanced• AI System Design Case Studies

Capstone kya banega

WHAT

Ek poora AI system design document: ek system choose karo, requirements se lekar failure modes aur trade-offs tak sab likho — har decision ke rationale aur measurement plan ke saath.

WHEN

L9 ka final deliverable — interview se pehle ka rehearsal aur portfolio ka artefact. Iske baad L10 (LLMOps) mein isi design ko operate karna seekhoge.

WHERE

Ek repo ya doc: requirement sheet, text/mermaid diagram, failure matrix, scaling notes, open questions — interviewer padh ke turant samajh jaaye.

Success criteria pehle likho: har section ke decisions saaf hon, har box ka why likha ho, aur koi bhi number fabricated na ho. Doc chhota chalega — clarity mandatory hai.

Scope: Ek system, ek workload. Feature list badhane se pehle failure matrix aur trade-offs section complete karo — wahi do sections interview mein sabse zyada ghuste hain.

Document skeleton

# <System> — AI Design Doc
1. Problem & users (job to be done)
2. Success criteria & constraints (latency, quality, privacy, cost budget)
3. Baseline (v0 kya simple chalta hai, uska measurement plan)
4. Architecture (boxes + arrows; har box ka 1-line why)
5. Data & knowledge flow (ingestion, retrieval, ACL, provenance, freshness)
6. Routing & model strategy (cascade, fallback, per-model evals)
7. Caching plan (kaunsa cache, key, TTL, hit-rate target jo measure karoge)
8. Reliability (timeouts, breaker, guardrails, degradation ladder, human gates)
9. Execution model (sync/async/queue, checkpoints)
10. Observability (metrics, traces, feedback -> eval cases, versioning)
11. Scaling (bottlenecks, 10x path)
12. Trade-offs & rejected alternatives
13. Open questions

Har section chhota: Teen-se-chhe line per section. Doc ka size nahi, decisions ki clarity matter karti hai — lambi doc padhi nahi jaati, defend toh bilkul nahi hoti.

Likhne ke rules

Har box ke saath: why, alternative jo reject, aur kaise measure hoga.
Numbers placeholders rakho jo tumhara system dena hai: "p95 <budget> — load test ke baad bharo" — fabricated benchmark kabhi nahi.
Failure matrix mandatory: component × failure × behaviour × owner (L9.6).
Caching section mein key + TTL + hit-rate metric likho (L9.5) — "cache lagayenge" kaafi nahi.
Doc bhi version hota hai: date + changelog — architecture badalta rehta hai.

Cost honesty: Cost section mein likho "per-feature token usage aur cache savings dashboard se measure karenge" — daam guess karna design nahi hai. L10 mein isko operate karoge.

Defence rehearsal

Har section se do sawaal anticipate karo: "10x traffic?", "provider outage?", "quality drop kaise pakde?"
Kamzori pehle khud bolo: "ye trade-off abhi open hai" — credibility badhti hai, chhupana nahi.
Baseline + measurement plan do — wahi proof hai ki tumhe pata hai kaise validate hoga.
Interview pace ka plan: pehle padh-phir draw-phir defend — aadhe ghante mein kya banega, pehle se soch lo.

Demo line: "Requirements se shuru, baseline measured, har box ka why likha hai — aur ye numbers main apne load test se bharunga." Yahi line poore L9 ka summary hai.

Exercise

Question: Decision ka reason wala hissa jo doc mein likhte hain — ek shabd, English?

Question: Sabse simple working version jisse shuruaat hoti hai — ek shabd, English?

Question: Fabricated numbers ki jagah interview mein kya batao? (do shabd, English)

Question: Doc ka aakhri section jo batata hai abhi kya decide nahi hua — do shabd, English?

Common mistakes

Diagram without rationale: Boxes draw, reasons nahi — interview mein har box par ruk jaoge. Har box ke saath why + rejected alternative mandatory likho.
Invented numbers: Benchmark/latency/cost guess karna sabse tez credibility killer. Har number ke saath measurement source batao — ya placeholder chhodo.
Failure aur scaling section skip: Happy-path design aadha design hai. Failure matrix aur 10x path ke bina interviewer ka pehla sawaal hi wahi hoga — section pehle se bharo.

Desi example: Ghar ka naksha — design doc ka desi analogy

Naksha mein sirf kamre nahi — pipe, wire, drain bhi hote hain kyunki wahi baad mein dukh dete hain. Design doc mein bhi boxes ke saath wiring (failure paths) honi chahiye:

boxes    = room layout (components)
wires    = failure paths + fallbacks (kya tootega)
written scale = nakshon par likha plan (measure karke bharo)

Interview angle — yahan se sawaal aate hain

Q: Design doc ke kaunse sections interview mein sabse zyada ghusste hain? (failure matrix, trade-offs, measurement plan, open questions)
Q: "10x traffic par kya karoge?" ka frame kya hoga? (bottleneck pehle → sharding/queue/cache → measurement plan)
Q: Cost section kaise likhoge bina numbers ke? (per-feature usage + savings metrics jo dashboard par aayenge — method, guess nahi)
Q: Apni design ki kamzori kaise present karoge? (open trade-off ke roop mein, rejected alternative ke saath — chhupane se worse)

Lesson complete?

L9 complete — ab tum requirement se architecture tak defend kar sakte ho. Agla level L10 (LLMOps): is design ko deploy, monitor aur cost-optimize karna.