Travel Booking

Legacy .NET Framework monolith → Azure microservices modernization

Travel Booking is the architectural blueprint and reference implementation for migrating a monolithic .NET Framework application (~40,000 users, ~600-table database) to a cloud-native, event-driven microservices architecture on Azure using .NET 9.

Status: Pre-Phase 1 — Phase 1 runs May 2026 to January 2027. Service scaffolding, shared libraries, and architecture design documents are complete; awaiting Phase 1 kickoff.

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Architecture Overview

The modernization follows the Strangler Fig pattern with Azure API Management (APIM) as the facade, progressively routing traffic from the legacy monolith to five bounded-context microservices.

graph TB
    Client["🌐 React 18 SPA"]
    APIM["🔗 Azure APIM<br/>(Gateway)"]
    
    Travel["✈️ Travel Booking"]
    Event["📅 Event Management"]
    Payment["💳 Payment"]
    Reporting["📊 Reporting"]
    Notification["🔔 Notification"]
    
    Bus["📮 Azure Service Bus<br/>(Topics & Queues)"]
    
    Client -->|All requests| APIM
    APIM -->|Route & Feature Flags| Travel
    APIM -->|Route & Feature Flags| Event
    APIM -->|Route & Feature Flags| Payment
    APIM -->|Route & Feature Flags| Reporting
    APIM -->|Route & Feature Flags| Notification
    
    Travel -->|Domain Events| Bus
    Event -->|Domain Events| Bus
    Payment -->|Domain Events| Bus
    Reporting -->|Subscribe Events| Bus
    Notification -->|Subscribe Events| Bus
    
    Travel -.->|Command Query| Bus
    Event -.->|Command Query| Bus
    Payment -.->|Command Query| Bus

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Core Architectural Patterns

Pattern	Implementation
Strangler Fig	APIM routes traffic to new services or legacy, with feature-flag-controlled progressive rollout
Transactional Outbox	Domain state + outbox message written in a single SQL transaction; MassTransit publishes to Service Bus
Saga Orchestration	MassTransit State Machine in Travel Booking for multi-step booking workflows with compensation
CQRS	Write services (Travel, Event, Payment) separated from read-optimized Reporting Service
Anti-Corruption Layer	Payment Service wraps the legacy payment system in Phase 1
Event-Driven Messaging	Service Bus Topics for pub/sub, Queues for point-to-point commands

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Microservices

Service	Responsibility	Key Patterns
Travel Booking	Search, itinerary management, booking lifecycle	Saga orchestrator, transactional outbox
Event Management	Event CRUD, scheduling, attendee registration	Domain events, pub/sub
Payment	Payment processing, refunds, reconciliation	Anti-corruption layer (legacy wrapper in Phase 1)
Reporting	Dashboards, analytics, data exports	Read-only materialized views from domain events
Notification	Email, SMS, push notifications	Event subscriber, template-based delivery

Each service follows Clean Architecture: API → Application → Domain → Infrastructure, with its own Azure SQL database.

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Tech Stack

Backend

Component	Technology
Runtime	.NET 9 / ASP.NET Core 9
ORM	Entity Framework Core 9
Messaging	MassTransit 8.3 + Azure Service Bus
CQRS/Mediator	MediatR 12.4
Resilience	Polly 8.5 (circuit breakers, retries)
Validation	FluentValidation 11.11
Mapping	Mapster 7.4
Logging	Serilog 9.0 → Application Insights
Auth	JWT Bearer + API Key
API Docs	Swashbuckle/Swagger 7.3
Testing	xUnit 2.9 · Moq 4.20 · FluentAssertions 7.2 · Coverlet 6.0

Frontend

Component	Technology
Framework	React 18.3 + TypeScript 5.7
Build	Vite 6.0
Routing	TanStack Router 1.92
Server State	TanStack Query 5.62
Client State	Zustand 5.0
Forms	React Hook Form 7.54 + Zod 3.24
Styling	TailwindCSS 4.0 + Radix UI
Real-time	SignalR 8.0
Charts	Tremor 3.18
i18n	i18next 24.2
Testing	Vitest 3.0 · Testing Library 16.1 · Playwright 1.49

Azure Infrastructure

Azure App Service · Azure SQL Database · Azure Service Bus · Azure API Management · Azure Front Door (CDN + WAF) · Application Insights · Azure Key Vault · Azure DevOps CI/CD

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Project Structure

TravelBooking/
├── src/
│   ├── Common/                            # Shared NuGet libraries
│   │   ├── TravelBooking.Common.Events/       #   Base IntegrationEvent, event contracts
│   │   ├── TravelBooking.Common.Logging/      #   Serilog config, correlation ID middleware
│   │   ├── TravelBooking.Common.HealthChecks/ #   SQL + Service Bus health check extensions
│   │   └── TravelBooking.Common.Security/     #   JWT Bearer + API Key auth handlers
│   │
│   ├── Services/                          # Microservices (Clean Architecture per service)
│   │   ├── TravelBooking/
│   │   │   ├── TravelBooking.API/         #   REST endpoints, middleware
│   │   │   ├── TravelBooking.Application/ #   MediatR handlers, DTOs, validators
│   │   │   ├── TravelBooking.Domain/      #   Entities, value objects, domain events
│   │   │   ├── TravelBooking.Infrastructure/ # EF Core, repositories, outbox
│   │   │   └── TravelBooking.Tests/       #   Unit + integration tests
│   │   ├── EventManagement/               #   (same 5-project structure)
│   │   ├── Payment/                       #   (same 5-project structure)
│   │   ├── Reporting/                     #   (same 5-project structure)
│   │   └── Notification/                  #   (same 5-project structure)
│   │
│   └── Frontend/                          # React 18 SPA
│       ├── src/
│       │   ├── app/                       #   Layout, router setup
│       │   ├── features/                  #   Feature-sliced modules (bookings, events, etc.)
│       │   ├── shared/                    #   Reusable components, hooks, utilities
│       │   └── mocks/                     #   MSW mock server for testing
│       └── e2e/                           #   Playwright E2E tests
│
├── Directory.Build.props                  # Shared .NET build settings
├── Directory.Packages.props               # Central NuGet version management
├── TravelBooking.slnx                         # Solution file
│
├── Technical_Assessment_Solution_Final_Version5.md   # Latest architecture design
├── Technical_Assessment_Solution_Final_Version4.md   # Previous architecture revision
├── [Nhan.Nguyen]Technical_Assessment_Solution.md     # Candidate's primary deliverable
├── TechSpec.md                            # Detailed technical specifications
├── PRD-Frontend-React18-SPA.md            # Frontend PRD (51 user stories)
├── Diagrams.md                            # Mermaid diagram sources
├── plan-travelBookings.prompt.md          # AI-assisted planning prompt
└── CLAUDE.md                              # AI agent configuration

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Getting Started

Prerequisites

• .NET SDK 9.0+
• Node.js 18+
• SQL Server 2019+ or Azure SQL Database
• Azure Service Bus namespace (or local emulator)

Backend

# Restore and build all services
dotnet restore TravelBooking.slnx
dotnet build TravelBooking.slnx

# Run tests
dotnet test TravelBooking.slnx

# Run a specific service
cd src/Services/TravelBooking/TravelBooking.API
dotnet run

Each service requires configuration in appsettings.json:

Key	Purpose
ConnectionStrings:DefaultConnection	Azure SQL connection string
AzureServiceBus:ConnectionString	Service Bus connection
Authentication:Authority	OAuth2/OIDC authority (Azure AD)
Authentication:SigningKey	JWT signing key
ApplicationInsights:InstrumentationKey	Telemetry key

Frontend

cd src/Frontend

npm install          # Install dependencies
npm run dev          # Dev server at http://localhost:5173
npm run build        # TypeScript check + production build → dist/
npm run test         # Vitest (single run)
npm run test:watch   # Vitest in watch mode
npm run test:coverage # Vitest with coverage
npm run test:e2e     # Playwright E2E tests
npm run typecheck    # TypeScript type checking (tsc --noEmit)
npm run lint         # ESLint + Prettier check
npm run lint:fix     # ESLint + Prettier auto-fix

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Testing Strategy

Layer	Tool	Scope
Backend Unit	xUnit + Moq + FluentAssertions	Domain logic, handlers, validators
Backend Integration	WebApplicationFactory	API endpoints, EF Core + in-memory DB
Code Coverage	Coverlet	Target: ≥80% on domain/application layers
Frontend Unit	Vitest + Testing Library	Components, hooks, utilities
Frontend E2E	Playwright	Full user journeys (booking, events, payments, dashboards, notifications)
API Mocking	MSW (Mock Service Worker)	Frontend tests against mocked backend

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Observability

• Structured Logging — Serilog with JSON output to Azure Application Insights
• Correlation IDs — Propagated across all services via CorrelationIdMiddleware
• Distributed Tracing — W3C Trace Context (traceparent header) across HTTP and Service Bus
• Health Checks — /health endpoint per service (SQL connectivity, Service Bus reachability)
• Metrics & Dashboards — Azure Monitor for response time, error rate, throughput
• Alerting — Dead-letter queue monitoring, circuit breaker state changes, health check failures

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Migration Timeline (Phase 1)

Milestone	Period	Focus
MS1 — Foundation	May–Jun 2026	IaC, CI/CD, APIM facade, observability, shared libraries
MS2 — Reporting	Jul–Aug 2026	First service extraction (read-only, lowest risk)
MS3 — Events + Notifications	Aug–Oct 2026	Event-driven messaging backbone
MS4 — Travel Booking	Nov 2026–Jan 2027	Saga orchestrator, core booking workflow
MS5 — Payment + Stabilization	Dec 2026–Jan 2027	Payment isolation, end-to-end testing, hardening

Team: 5 backend engineers + frontend and DevOps resources.

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Documentation

Document	Description
Technical Assessment Solution (Latest)	Complete architecture design with diagrams and ADRs (v5)
Technical Assessment Solution (v4)	Previous architecture revision
Candidate Deliverable	Primary technical assessment submission (2026-03-21)
Technical Specification	Event payloads, error handling, retry strategies, API contracts
Frontend PRD	51 user stories, acceptance criteria, UX specifications
Architecture Diagrams	Mermaid source for all architecture diagrams
Original Assessment Brief	Requirements, constraints, and evaluation criteria

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License

Not yet specified.