Phase 3: Design & Architecture

Phase 3: Design & Architecture

Modernization Overlay: Apply the 2026 Modernization Addendum controls (AI assist + RTG linkage) before phase exit.

Purpose

Define how the product will look and work (UI/UX), and design the technical architecture that supports feature requirements.

Duration

2-3 weeks

Key Activities

3.1 UX/UI Design

• Lead: Product Designer

• Tools: Figma, Adobe XD

• File Location: Figma project: [ProductName] Design System

Deliverables:

1. Design System

• ├─ Color palette (primary, secondary, feedback colors)

• ├─ Typography (heading, body, button text styles) ├─ Component library

│├─ Button (variations: primary, secondary, disabled) │├─ Input fields

• │├─ Modals

• │├─ Cards

• │└─ Navigation components

• └─ Layout guidelines (margins, spacing, grid)

2. Wireframes

• ├─ Low-fidelity wireframes (for planning) └─ Medium-fidelity (showing structure & interaction)

3. High-Fidelity Mockups

• ├─ Login Screen

• ├─ Dashboard

• ├─ Payment Flow (4 screens)

• ├─ Settings

• └─ Error states

4. Prototypes

├─ Interactive prototype (Figma) └─ User flow animations

5. Design Documentation

├─ Design rationale (why certain choices) ├─ Accessibility specs (color contrast, font sizes) └─ Responsive design breakpoints

• Mobile: 320px - 640px

• Tablet: 641px - 1024px

• Desktop: 1025px+

Figma File Structure:

Figma Project: [ProductName] Design System

• ├─ Design System │├─ Colors │├─ Typography │└─ Components ├─ Screens │├─ 01-Auth │├─ 02-Dashboard

• │├─ 03-Payment │└─ 04-Settings └─ Prototypes └─ User Flow

• └─ Requirement Mapping │├─ REQ IDs linked per frame/component │└─ Coverage board (Designed/In Review/Approved)

• 3.2 Software Architecture Design

  • Lead: Technical Lead / Solutions Architect

  • Document: [ProjectCode]-020-System-Architecture-v1.0.docx

  • Tools: Draw.io, Lucidchart

Architecture Document Contents:

1. Architecture Overview

• High-level system diagram showing:

• Frontend (Web, Mobile)

• API Gateway

• Microservices

• Databases

• External integrations

• Message queues

• Caching layer

1. Component Architecture

• ├─ Frontend Service │├─ React application

• │├─ State management (Redux)

│└─ HTTP client (Axios) │ ├─ API Gateway │├─ Authentication & authorization

• │├─ Request validation

│└─ Rate limiting │ ├─ Backend Services

• │├─ User Service

• ││├─ User registration

• ││├─ Profile management

• ││└─ Auth tokens ││

• │├─ Payment Service

• ││├─ Payment processing

• ││├─ Refunds

││└─ Transaction history ││

│└─ Notification Service │ ├─ Email notifications │ └─ SMS alerts │ ├─ Databases │├─ PostgreSQL (transactional data) │├─ Redis (cache, sessions) │└─ Elasticsearch (search/logs) │ └─ External Services ├─ Payment Gateway (Stripe) ├─ Email Service (SendGrid) └─ SMS Service (Twilio)

1. Database Schema (Entity Relationship Diagram) ├─ Users table │├─ user_id (PK) │├─ email (unique) │├─ password_hash │├─ created_at │└─ updated_at │ ├─ PaymentMethods table │├─ payment_method_id (PK) │├─ user_id (FK) │├─ card_token (encrypted) │└─ is_default │ └─ Transactions table ├─ transaction_id (PK) ├─ user_id (FK) ├─ payment_method_id (FK) ├─ amount ├─ status └─ created_at

2. API Specifications POST /api/v1/auth/register ├─ Request: {│ "email": "user@example.com",│ "password": "secure_password",│ "name": "User Name"│

}│ ├─ Response (201): {│ "user_id": "uuid",│ "email": "user@example.com",│ "auth_token": "jwt_token"│ }│ └─ Errors: 400: Invalid input 409: Email already registered 500: Server error POST /api/v1/payments/process ├─ Request: {│ "payment_method_id": "uuid",│ "amount": 99.99,│ "currency": "USD"│ }│ ├─ Response (200): {│ "transaction_id": "uuid",│ "status": "completed",│ "timestamp": "2025-12-06T10:30:00Z"│ }│ └─ Errors: 400: Invalid amount 402: Payment declined 500: Processing error 5. Security Architecture ├─ Authentication: JWT tokens ├─ Authorization: Role-based access control (RBAC) ├─ Data Encryption: │├─ TLS 1.2+ for transit │├─ AES-256 for sensitive data at rest │└─ bcrypt for password hashing ├─ API Security: │├─ Rate limiting │├─ CORS policy │└─ SQL injection prevention (parameterized queries) └─ Compliance: ├─ PCI DSS v3.2 (payment data)

├─ GDPR (user privacy) └─ SOC 2 Type II (general security)

1. Scalability & Performance ├─ Load Balancing: Nginx/HAProxy ├─ Horizontal Scaling: │├─ Stateless services │├─ Container orchestration (Kubernetes) │└─ Auto-scaling policies ├─ Caching Strategy: │├─ Redis for sessions │├─ CDN for static assets │└─ Database query caching ├─ Performance Targets: │├─ API response time: <200ms │├─ Page load time: <3s │└─ Database query time: <100ms

2. Deployment Architecture ├─ Development Environment │└─ Docker Compose local setup ├─ Staging Environment │├─ Pre-production replica │└─ Blue-green deployment ready └─ Production Environment ├─ Kubernetes cluster (3 nodes minimum) ├─ Auto-scaling (2-10 pods per service) ├─ Multi-region setup (primary + failover) └─ Disaster recovery (backup strategy)

3. Monitoring & Observability ├─ Metrics: Prometheus │├─ Request rate │├─ Error rate │├─ Response time │└─ CPU/Memory usage ├─ Logging: ELK Stack │└─ Centralized logs from all services ├─ Tracing: Jaeger │└─ Distributed request tracing └─ Alerting: PagerDuty └─ Critical alerts wake on-call engineer

3.3 High-Level Design Document (HLD)

• Lead: Solutions Architect

• Document: [ProjectCode]-021-High-Level-Design-v1.0.docx

Similar to architecture but with more narrative explanation of design decisions and tradeoffs.

3.4 Low-Level Design Document (LLD)

• Lead: Tech Lead / Senior Developer

• Document: [ProjectCode]-022-Low-Level-Design-v1.0.docx

Contents:

For each major component:

1. Component Name: User Service

2. Responsibilities

• User registration & login

• Profile management

• Password reset

• Token generation

3. Class Diagram

UserService

├─ registerUser(email, password) ├─ loginUser(email, password) ├─ getUserProfile(userId) ├─ updateProfile(userId, data) ├─ resetPassword(email) └─ validateToken(token)

1. Sequence Diagram

User -> API -> UserService -> Database

├─ Request: POST /register ├─ UserService.registerUser() ├─ Hash password ├─ Save to database

• └─ Return: user_id, auth_token

5. Error Handling

├─ Duplicate email → 409 Conflict ├─ Invalid password format → 400 Bad Request ├─ Database error → 500 Server Error

6. Dependencies

• ├─ bcrypt library (password hashing) ├─ JWT library (token generation) └─ PostgreSQL driver

7. Testing Strategy

• ├─ Unit tests: 90%+ coverage

• ├─ Integration tests: API + Database └─ Acceptance tests: User registration workflow

3.5 Database Design Document

• Lead: Database Administrator / Backend Lead

• Document: [ProjectCode]-023-Database-Design-v1.0.docx

• Includes:

  • Detailed ERD with all tables, columns, relationships

  • Index strategy (which queries need indexes)

  • Backup & recovery strategy

  • Data migration plan (if updating existing system)

  • Performance expectations

• 3.6 API Specification Document

  • Lead: Backend Lead

  • File: [ProjectCode]-024-API-Specification-v1.0.docx (or OpenAPI/Swagger)

  • Location: Swagger UI or Postman collection

Format (OpenAPI 3.0):

openapi : 3.0.0 info : title : Payment App API version : 1.0.0

servers :

- url : https://api.paymentapp.com/v1

paths : /auth/register : post : summary : Register a new user requestBody : required : true content : application/json : schema : type : object

properties : email : type : string password : type : string responses : 201 : description : User created successfully content : application/json : schema : type : object properties : user_id : type : string auth_token : type : string

3.7 Design Review & Approval

• Lead: PM + Tech Lead

• Activities:

  • Design review meeting (1.5 hours)

  • Stakeholder sign-off on designs

  • Architecture review with senior engineers

  • Document any design decisions in Confluence

Design Review Checklist:

• ☐ Does the design address all requirements? ☐ Is the architecture scalable for projected growth? ☐ Are there security vulnerabilities? ☐ Can the team implement with available skills? ☐ Are there external dependencies that could block? ☐ Is the design documented sufficiently?

• ☐ Have we considered performance implications? ☐ Is the database schema normalized properly? ☐ Do we have monitoring/observability built in? ☐ Is disaster recovery/backup strategy adequate? ☐ Is every approved Figma frame linked to at least one requirement ID in RTG?

Deliverables Checklist

Success Criteria

✅ All screens designed and approved

✅ Architecture accommodates scalability needs

✅ API spec complete and reviewed

✅ Database design normalized and optimized

• ✅ Security architecture reviewed and approved

✅ No unknowns remaining (all questions answered)