Cheatsheet — Base.vn Interview Prep

🎯 Universal Clarify (chọn 5-8)

① Functional scope + out-of-scope
② Scale: DAU, RPS peak, Read:Write
③ Latency p50/p95/p99
④ Consistency strong/eventual
⑤ Multi-tenant isolation
⑥ Auth/permission/RBAC
⑦ Real-time poll/push
⑧ Data lifecycle (retention, GDPR)
⑨ Mobile/offline
⑩ 3rd-party/webhook
⑪ Compliance (PII, audit, region)
⑫ SLA/DR/RTO/RPO
⑬ Cost/OSS-SaaS
⑭ Team stack familiarity

→ Chi tiết

⚡ 5-Step Design Framework

1. Clarify (5m) — chọn 5-8 từ Universal
2. API (5m) — endpoint, request/response, auth
3. Data model (10m) — tables, FK, index
4. Architecture (5m) — client → API → DB + cache/queue
5. Trade-offs (5m) — gì optimized, gì sacrificed, failure mode

💡 Nói ra suy nghĩ. Chấm reasoning, không đáp án.

⚙️ Backend Stack Quick

REST: GET 200/206 · POST 201/202 · PUT/PATCH 200/204 · DEL 204
Status: 400 bad · 401 unauth · 403 forbidden · 404 NF · 409 conflict · 422 validation · 429 rate · 5xx
JWT: access 15m (memory) + refresh 7d (httpOnly cookie, rotate)
Index: equality TRƯỚC range. (user_id, created_at DESC)
Transaction: multi-table write → $transaction
N+1: log SQL → include/select. DataLoader cho GraphQL.
Cache: Cache-aside default. TTL + jitter. Lock cho stampede.
Queue: BullMQ. Idempotency key. Retry exp backoff. Per-channel queue.

→ Chi tiết BE

🎨 Frontend Stack Quick

Hooks: useState · useEffect (cleanup!) · useMemo (đo trước) · useCallback (chỉ khi pass to memo)
TanStack Query: staleTime (fresh window) vs gcTime (memory). Key factory. Invalidate sau mutation.
Optimistic: onMutate set, onError rollback.
RSC: default server. "use client" cho interactive leaf.
Next caching: request memo · data cache · route cache · router cache. revalidateTag.
Perf: Profiler đo trước. Code split. Virtual list. Bundle analyzer.
CWV: LCP < 2.5s · INP < 200ms · CLS < 0.1
JWT lưu: memory (NOT localStorage)

→ Chi tiết FE

🏢 Multi-tenancy ★

Pattern	Pros	Cons
Shared schema (tenant_id col)	Cheap, scale dễ	Leak risk
Schema per tenant	Isolation tốt	Migration n×
DB per tenant	Strict isolation	Cost cao

Enforce: Middleware inject tenantId từ JWT + Postgres RLS safety net.

🧭 SOLID

Single Responsibility — 1 lý do thay đổi
Open/Closed — extend, không sửa (strategy)
Liskov — subclass dùng được như parent
Interface segregation — interface nhỏ > bloat
Dependency inversion — abstraction, inject

→ Ví dụ

📏 YAGNI · KISS · DRY

YAGNI — đừng build feature trước khi cần. NOT cho security/schema/PII.
KISS — đơn giản > clever. Function < 30 line.
DRY — 1 source of truth. Nhưng AHA > DRY — wait 3-4 lần để biết pattern.

⚡ Quick-fire

SQL/NoSQL: SQL = JOIN+transaction. NoSQL = write-heavy+flex schema.
JWT/Session: JWT stateless+mobile. Session-Redis revoke.
PUT/PATCH: PUT replace full. PATCH partial.
401/403: 401 = ai. 403 = không có quyền.
Microservice: chỉ khi team > 2-3 squad + scale độc lập.
Idempotency: POST → idempotency-key header.
Cache stampede: lock + SWR + jitter TTL.
Read replica: read-after-write về primary.

💬 Behavioral STAR

Situation → Task → Action → Result. ~3 min/câu.

Bug khó: race / leak / N+1 / stampede — không "typo"
Disagreement: listen → data → spike thử cả 2
Why Base.vn: impact (1000+ DN) + stack overlap + multi-tenant + sản phẩm thực + 1-2 product cụ thể

🦀 Rust pitch (sales_agent)

"Em build Rust backend với Axum + sqlx — scan card, parse contact, push HubSpot. Pattern giống NestJS: module-per-feature, repo tách handler, error enum → HTTP qua trait. Rust ép em handle Option/Result, ít bug null. Pick Rust vì job xử ảnh + AI nặng — tokio concurrent tốt, footprint nhỏ."

→ Code examples

🎯 Mock Design Q (30 min/câu)

Trade-offs để nói: shared schema + RLS · queue per channel · presigned S3 URL · state machine · data-driven config

✅ Pre-interview Checklist

☐ Test camera, mic, internet
☐ Mở sẵn IDE để share screen
☐ Notepad ghi câu hỏi clarify
☐ Mở sẵn page này (cheatsheet)
☐ Coffee xong, nước cạnh tay
☐ STAR stories review 1 lần
☐ "Why Base.vn?" answer review
☐ Join 5-10 phút sớm
☐ Hít sâu — biết mình giỏi

Base.vn Prep

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