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Lessons (40)

• API Contracts, Gateways and Security

  Make APIs evolvable and safe with explicit formats, versioning, idempotency, gateway policy, authentication and authorization. ![API boundary: a …

• Services & Ingress

  … shop-api spec: selector: app: shop-api send traffic to pods with this label… ports: - port: 80 …when …

• Proxies, APIs and Real-Time Protocols

  … reverse proxy at the edge, request APIs, queues and persistent real-time connections](/img/system-design-l6/protocols …

• Deployments, ReplicaSets & Rollouts

  … shop-api, version: "1.8.0" } spec: containers: - name: api image: registry.example.com/shop-api:1.8 …

• API Gateway, BFF & Service Discovery

  … 100 }] - path: /api/orders service: http://orders-svc:8080 plugins: [jwt-auth] - path: /api/products service: http://catalog …

• Helm, kubectl Cheat Sheet & Best Practices

  … 512Mi } bash helm upgrade --install shop-api ./shop-api -f values-prod.yaml -n prod helm template ./shop …

• REST vs GraphQL vs gRPC

  … user (30 fields, needs 2) App- API: GET /users/42/posts?limit=3 API-- App: posts App- API …

• Docker & Containers

  … docker run -d -p 3000:3000 --name api -e DATABASE URL=postgres://… shop-api:1.0 docker logs …

• ConfigMaps, Secrets & Storage

  … non-secret settings yaml apiVersion: v1 kind: ConfigMap metadata: name: shop-api-config data: LOG LEVEL: "info" FEATURE …

• REST API Design

  Design APIs that are predictable and pleasant to use: resource naming, methods, status codes, pagination, versioning, errors and …

• Kubernetes Cluster Architecture

  … team-shop"] a1[shop-api] --- a2[shop-web] end subgraph NS2["namespace: team-payments"] b1[payments-api] end …

• Why Kubernetes?

  … shop-api } template: metadata: labels: { app: shop-api } spec: containers: - name: api image: registry.example.com/shop-api …

• Pods

  … registry.example.com/shop-api:1.8.0 command: ["npm", "run", "migrate"] containers: - name: api image: registry.example …

• Authentication, Authorization & API Security

  … server can verify Best for Traditional web apps APIs, mobile apps, microservices Common pattern: a short-lived access …

• Frontend Security

  … true App- API: GET /orders (with cookie) API-- App: 200 + data ✅ (browser lets JS read it) - CORS is …

• Scaling & Health Probes

  … shop-api spec: scaleTargetRef: { apiVersion: apps/v1, kind: Deployment, name: shop-api } minReplicas: 3 maxReplicas: 30 metrics: - type …

• Frontend Testing Strategy

  … 49.99 }]), ), http.post("/api/cart", () = new HttpResponse(null, { status: 201 })), ]; tsx it("lists products from the API …

• Vertical Slice Architecture & the Modular Monolith

  … 2. Each module has a public API (a facade or interface); everything else is internal . 3. No reaching …

• Premiere-Night Video Streaming

  Let millions press Play together by separating small control-plane APIs from CDN-delivered video bytes. The big …

• Serverless Architecture

  … static frontend"] U -- APIG[API Gateway] APIG -- Auth["🔐 Cognito / Auth0"] APIG -- L1["λ orders API"] L1 -- DDB[(DynamoDB …

• Design a File Storage Service

  Upload bytes directly to object storage while the API owns durable metadata, authorization, sharing and synchronization. ![File storage …

• State Management (Redux, Zustand, TanStack Query)

  … useQuery(["products"]) Q- API: ONE request (deduplicated) API-- Q: data Q-- A: data Q-- B: data Note over …

• TypeScript Essentials

  … string undefined ts // A typed API helper async function fetchJson<T (url: string): Promise<T { const response = await …

• Backend Languages: Node.js, Go, Python & Rust

  … How each handles concurrency, what it's best at, and the same tiny API written in all four …

• Deploying & Operating Microservices

  CI/CD per service, blue-green and canary releases, feature flags, API versioning, distributed tracing and the production …

• Next.js Rendering: CSR, SSR, SSG, ISR & Server Components

  … download + run JavaScript B- API: fetch products API-- B: JSON Note over B: ✅ page visible (late) ✅ Rich interactivity …

• Monolith vs Microservices

  … many deployables"] direction LR GW[API Gateway] -- US[Users svc] -- UDB[(users DB)] GW -- OS[Orders svc] -- ODB …

• Data in Microservices: Sagas & the Outbox Pattern

  … database per service Each service owns its data. Nobody else touches its tables , only its API and events …

• I — Interface Segregation Principle

  … app each get an API shaped for their needs, instead of one giant API. - GraphQL: clients request only …

• Which Pattern Do I Need?

  … themes, providers)"] -- AF[Abstract Factory] P4["3rd-party API doesn't<br/ fit my interface"] -- AD[Adapter] P5 …

• Scaling, Load Balancing & Rate Limiting

  … Very fast, doesn't read HTTP. - L7 (application): reads HTTP, so it can route /api/ to API servers …

• System Design Interview Framework

  … 5. Define APIs with authorization and idempotency. 6. Deep dive into the hard invariant/bottleneck. 7. Close with …

• Design a Social Media Feed

  … write a post once, then fan out to inboxes or merge on read behind a cached timeline API …

• JavaScript Essentials: Event Loop, Closures & this

  … call stack, Web APIs, task queues](/img/frontend/event-loop.svg) Part Kitchen analogy Role --- --- --- Call stack The …

• Message Queues & RabbitMQ

  … user waits for everything"] direction LR U1[Signup API] -- E1[Send email 2s] -- P1[Resize avatar 3s] -- A1 …

• Onion Architecture & Clean vs Hexagonal vs Onion

  … infrastructure, UI, tests Implementations of the interfaces, web framework, DB, external APIs SqlOrderRepository , controllers, EF Core / Prisma mermaid …

• Finding Service Boundaries with DDD

  … nobody else reads its tables. - Shares data only through APIs and events . - Keeps only the data it needs …

• S — Single Responsibility Principle

  … id }) { const [user, setUser] = useState(null); useEffect(() = { fetch( /api/users/${id} ).then((r) = r.json()).then(setUser); }, [id …

• DRY: Don't Repeat Yourself

  … shared schema (for example, Zod) used by both API types written by hand in the client Generate types …

• Comments & Formatting

  … remove after v2 migration, see TICKET-481 Public API docs JSDoc on exported functions Clarify a regex or …