✈️ Flight Booking System (FBS)

A production-grade .NET 10 flight seat reservation system built with Clean Architecture, Domain-Driven Design (DDD), and CQRS, fully deployed to Microsoft Azure.

📋 Table of Contents

Overview
Architecture
Azure Infrastructure
Technologies
Project Structure
API Endpoints
Domain Model
Getting Started
Configuration
CI/CD
Monitoring

🔍 Overview

FBS allows passengers to search for flights, reserve seats, confirm or cancel reservations, and receive email notifications at each lifecycle stage. The system enforces a 10-minute confirmation window — unconfirmed reservations are automatically expired and their seats released.

Core Features

Flight Search — search available flights by route and date with real-time seat availability
Seat Reservation — reserve a specific seat with conflict prevention via optimistic concurrency (RowVersion)
Reservation Lifecycle — Pending → Confirmed / Cancelled / Expired
Automatic Expiration — Azure Function Timer trigger expires unconfirmed reservations every 2 minutes
Email Notifications — event-driven email notifications at every lifecycle transition via Mailtrap API
Resilient HTTP — Polly v8 standard resilience pipeline (retry + circuit breaker) for outbound HTTP calls

🏗️ Architecture

Clean Architecture Layers

┌─────────────────────────────────────────────────────┐
│               FBS.API  (Presentation)               │
│    REST Controllers · GlobalExceptionHandler        │
│    OpenTelemetry (OTLP → New Relic)                 │
└──────────────────────────┬──────────────────────────┘
                           │
┌──────────────────────────▼──────────────────────────┐
│            FBS.Application  (Use Cases)             │
│  Commands · Queries · DTOs · FluentValidation       │
│  MediatR Pipeline: Logging · Validation · Tx        │
└──────────────────────────┬──────────────────────────┘
                           │
┌──────────────────────────▼──────────────────────────┐
│              FBS.Domain  (Business Logic)           │
│   Aggregates · Value Objects · Domain Events        │
│   Business Rules · Specifications · Result<T>       │
└──────────────────────────┬──────────────────────────┘
                           │
┌──────────────────────────▼──────────────────────────┐
│           FBS.Infrastructure  (Data & I/O)          │
│   EF Core · Repositories · UnitOfWork               │
│   ServiceBusEventPublisher · DomainEventDispatcher  │
└─────────────────────────────────────────────────────┘

Key Patterns

Pattern	Implementation
CQRS	Full separation: Commands (write) and Queries (read) via MediatR. Shared Azure SQL database.
DDD	Aggregates (`Flight`, `Reservation`), Value Objects (`FlightNumber`, `SeatNumber`, `Email`), Domain Events
Repository + Unit of Work	`IFlightRepository`, `IReservationRepository`, `IUnitOfWork` — EF Core implementations in Infrastructure
Specification Pattern	`ExpiredReservationsSpecification`, `ReservationsByFlightSpecification` for reusable query logic
Pipeline Behaviors	`ValidationBehavior` (FluentValidation), `TransactionBehavior` (EF Core), `LoggingBehavior`
Result Pattern	`Result<T>` with `ErrorType` instead of throwing exceptions for business failures
Domain Events	Raised inside aggregates, dispatched after `SaveChanges` via `IDomainEventDispatcher`
Managed Identity	Passwordless auth from App Service and Functions to SQL, Service Bus, Storage

☁️ Azure Infrastructure

All infrastructure is described as code with Bicep (infra/) and deployed via GitHub Actions.

Azure Resource Group: rg-fbs-dev (West Europe)
│
├── App Service (Linux B1)          fbs-dev
│   └── FBS.API  →  Azure SQL (Poland Central)
│
├── Azure Function (Consumption)    fbns-func-dev
│   └── FBS.Function.Notifications
│       Service Bus Trigger → Mailtrap API
│
├── Azure Function (Consumption)    expire-func-dev
│   └── FBS.Function.ExpiredReservations
│       Timer Trigger (every 2 min) → Azure SQL
│
├── Azure Service Bus (Basic)       fbs-servicebus-dev
│   └── Queue: reservation-events
│
├── Azure SQL (Basic 5 DTU)         fbs-sql-server-dev / fbs-db-dev
│
├── Storage Account                 storagefbsdev
│   (Functions runtime state, Timer trigger locks)
│
└── Application Insights            fbs-dev
    (shared across all three applications)

Managed Identity RBAC

Principal	Resource	Role
`fbs-dev`	Azure SQL	`db_datareader` + `db_datawriter`
`fbs-dev`	Service Bus	`Azure Service Bus Data Sender`
`fbns-func-dev`	Service Bus	`Azure Service Bus Data Receiver`
`fbns-func-dev`	Storage	Blob Owner · Queue Contributor · Table Contributor
`expire-func-dev`	Azure SQL	`db_datareader` + `db_datawriter`
`expire-func-dev`	Service Bus	`Azure Service Bus Data Sender`
`expire-func-dev`	Storage	Blob Owner · Queue Contributor · Table Contributor

🛠️ Technologies

Core

Technology	Version	Purpose
.NET / ASP.NET Core	10.0	API framework
Entity Framework Core	10.0	ORM, Code-First migrations
Azure SQL	—	Relational database
MediatR	12.x	CQRS, pipeline behaviors
FluentValidation	11.x	Request validation

Azure & Cloud

Technology	Purpose
Azure App Service (Linux)	Hosts FBS.API
Azure Functions v4 (Windows, isolated)	Notifications and expiration background processing
Azure Service Bus	Event-driven messaging between API and Functions
Azure SQL	Database with Entra-ID-only authentication
Azure Storage	Functions runtime state and distributed timer locks
Azure Managed Identity	Passwordless auth across all Azure services

Observability & DevOps

Technology	Purpose
Application Insights	Telemetry, live metrics, log stream
New Relic APM	Distributed tracing, error inbox, performance dashboards
OpenTelemetry (OTLP/HTTP)	Vendor-neutral instrumentation for Linux App Service
GitHub Actions	4 CI/CD pipelines (Infrastructure + 3 app deployments)
Bicep	Infrastructure as Code
OIDC Workload Identity Federation	Passwordless GitHub → Azure authentication

Libraries

Library	Purpose
Polly v8 / Microsoft.Extensions.Http.Resilience	HTTP retry + circuit breaker
Bogus	Flight seed data generation
Mailtrap API	Email delivery (sandbox)

📁 Project Structure

flight-booking-system/
├── src/
│   ├── FBS.API/                          # ASP.NET Core Web API (Linux App Service)
│   │   ├── Controllers/                  # FlightsController, ReservationsController
│   │   ├── DTOs/                         # Request DTOs
│   │   ├── Middlewares/                  # GlobalExceptionHandler (ValidationProblemDetails)
│   │   └── Program.cs                    # App bootstrap, OpenTelemetry setup
│   │
│   ├── FBS.Application/                  # Use cases (no framework dependencies)
│   │   ├── Commands/                     # CreateReservation, ConfirmReservation,
│   │   │                                 # CancelReservation, ExpireReservation
│   │   ├── Queries/                      # GetAvailableFlights, GetFlightByNumber,
│   │   │                                 # GetReservation
│   │   └── Common/
│   │       ├── Behaviors/                # ValidationBehavior, TransactionBehavior,
│   │       │                             # LoggingBehavior
│   │       └── Result/                   # Result<T>, ErrorType
│   │
│   ├── FBS.Domain/                       # Pure business logic, no dependencies
│   │   ├── Flight/                       # Flight aggregate, Seat, Value Objects,
│   │   │                                 # SeatReservedEvent, SeatReleasedEvent
│   │   ├── Reservation/                  # Reservation aggregate, Value Objects,
│   │   │                                 # ReservationCreated/Confirmed/Cancelled/ExpiredEvent
│   │   ├── Common/
│   │   │   ├── Base/                     # AggregateRoot<T>, Entity<T>, DomainEventBase
│   │   │   ├── Rules/                    # Business rule classes + IBusinessRule
│   │   │   └── Specifications/           # Specification<T>, ExpiredReservationsSpecification
│   │   ├── Repositories/                 # IFlightRepository, IReservationRepository, IUnitOfWork
│   │   └── SharedKernel/                 # Email, PhoneNumber, Airport value objects
│   │
│   ├── FBS.Infrastructure/               # EF Core, repositories, external services
│   │   ├── Persistence/                  # ApplicationDbContext, EF configs, migrations
│   │   ├── EventDispatcher/              # IDomainEventDispatcher, post-save dispatch
│   │   ├── Events/                       # ServiceBusEventPublisher, EventMapper, DTOs
│   │   ├── BackgroundJobs/               # ExpireReservationsJob (used by Azure Function)
│   │   └── Seed/                         # FlightDataSeeder (Bogus)
│   │
│   ├── FBS.Function.Notifications/       # Azure Function — Service Bus trigger
│   │   ├── Functions/                    # ProcessReservationEventFunction
│   │   │                                 # Complete/Abandon/DeadLetter settlement
│   │   ├── Notification/                 # NotificationService
│   │   ├── Email/                        # MailtrapApiEmailService, options
│   │   └── Templates/                    # EmailTemplates (HTML)
│   │
│   └── FBS.Function.ExpiredReservations/ # Azure Function — Timer trigger
│       └── Functions/                    # ExpireReservationsFunction (every 2 min)
│
├── infra/                                # Bicep Infrastructure as Code
│   ├── main.bicep
│   ├── main.bicepparam
│   └── modules/                          # app-insights, api-app, function-app,
│                                         # service-bus, sql, storage
│
├── .github/workflows/
│   ├── 01-infrastructure.yml             # Bicep deploy (on infra/** changes)
│   ├── 02-deploy-api.yml                 # Build + deploy FBS.API
│   ├── 03-deploy-notifications.yml       # Build + zip-deploy FBS.Function.Notifications
│   └── 04-deploy-expire.yml              # Build + zip-deploy FBS.Function.ExpiredReservations
│
├── postman/
│   ├── FBS-API.postman_collection.json   # 26 test cases with pre-request scripts
│   ├── FBS-Local.postman_environment.json
│   └── FBS-AzureDev.postman_environment.json
│
└── scripts/
    └── setup-rbac.ps1                    # One-time RBAC role assignment script

🔌 API Endpoints

Flights

Method	Endpoint	Description	Response
`GET`	`/api/flights/search?departureAirport=BCN&arrivalAirport=ATL&date=2026-04-08`	Search flights by route and date	`200 FlightSummaryDto[]`
`GET`	`/api/flights/{flightNumber}`	Get flight details with full seat map	`200 FlightDetailsDto` / `404`

Reservations

Method	Endpoint	Description	Response
`POST`	`/api/reservations/create`	Create a new Pending reservation	`201 CreateReservationResponse`
`GET`	`/api/reservations/get/{id}`	Get reservation details	`200 ReservationDetailsDto` / `404`
`PUT`	`/api/reservations/confirm/{id}`	Confirm a Pending reservation	`204` / `409`
`DELETE`	`/api/reservations/cancel/{id}`	Cancel a Pending reservation	`204` / `409`

Example: Create Reservation

POST /api/reservations/create

{
  "flightNumber": "AA387",
  "seatNumber": "5C",
  "firstName": "John",
  "lastName": "Doe",
  "email": "john.doe@example.com",
  "phone": "+380971234567"
}

201 Created:

{
  "reservationId": "3fa85f64-5717-4562-b3fc-2c963f66afa6",
  "flightId": "fb29e71f-5219-4dc9-8b8b-daf709de2afb",
  "flightNumber": "AA387",
  "seatNumber": "5C",
  "passengerName": "John Doe",
  "status": "Pending",
  "createdAt": "2026-04-08T10:00:00Z",
  "expiresAt": "2026-04-08T10:10:00Z"
}

🎯 Domain Model

Aggregates

Flight

Flight (AggregateRoot) → owns Seat collection
Value Objects: FlightId, FlightNumber, SeatNumber, Airport
Domain Events: SeatReservedEvent, SeatReleasedEvent
Business Rules: seat must be available to reserve; seat must be reserved to release

Reservation

Reservation (AggregateRoot)
Value Objects: ReservationId, PassengerInfo, Email, PhoneNumber
States: Pending → Confirmed | Cancelled | Expired
Domain Events: ReservationCreatedEvent, ReservationConfirmedEvent, ReservationCancelledEvent, ReservationExpiredEvent
Business Rules:
- ReservationMustBePendingToConfirmRule
- ReservationMustNotBeExpiredToConfirmRule
- CannotCancelNonPendingReservationRule (Pending only; Confirmed/Expired/Cancelled → 409)
- OnlyPendingReservationsCanExpireRule

Event Flow

FBS.API
  └─► CreateReservationCommandHandler
        ├─► Flight.ReserveSeat()  → SeatReservedEvent (internal)
        ├─► Reservation.Create()  → ReservationCreatedEvent
        └─► UnitOfWork.SaveChanges()
              └─► DomainEventDispatcher
                    └─► ServiceBusEventPublisher
                          └─► Service Bus Queue: reservation-events
                                └─► FBS.Function.Notifications
                                      └─► MailtrapApiEmailService

🚀 Getting Started

Prerequisites

.NET 10 SDK
SQL Server (LocalDB is sufficient for local development)
Azure Functions Core Tools v4 (for running Functions locally)
Azurite (local Azure Storage emulator)
Azure CLI (az login for Managed Identity local development)

Local Setup

1. Clone the repository

git clone https://github.com/komenday/flight-booking-system.git
cd flight-booking-system

2. Configure appsettings.Development.json in FBS.API

{
  "ConnectionStrings": {
    "DefaultConnection": "Server=(localdb)\\mssqllocaldb;Database=FBS_Dev;Trusted_Connection=True;"
  }
}

3. Apply migrations and seed data

cd src/FBS.Infrastructure
dotnet ef database update --startup-project ../FBS.API

Migrations run automatically on startup. Seed data (15 random flights) is inserted if the Flights table is empty.

4. Run the API

cd src/FBS.API
dotnet run

Swagger UI: http://localhost:5000/swagger

5. Run Functions locally (optional)

Start Azurite, then in separate terminals:

cd src/FBS.Function.Notifications
func start

cd src/FBS.Function.ExpiredReservations
func start

Database Migrations

# Add a new migration
dotnet ef migrations add MigrationName \
  --project src/FBS.Infrastructure \
  --startup-project src/FBS.API

# Apply migrations
dotnet ef database update \
  --project src/FBS.Infrastructure \
  --startup-project src/FBS.API

⚙️ Configuration

FBS.API — `appsettings.json`

{
  "ConnectionStrings": {
    "DefaultConnection": ""
  },
  "ServiceBus": {
    "FullyQualifiedNamespace": "fbs-servicebus-dev.servicebus.windows.net",
    "QueueName": "reservation-events",
    "TimeoutSeconds": 30,
    "MaxRetryAttempts": 3
  },
  "EventPublisher": {
    "BaseUrl": "",
    "RetryCount": 3,
    "TimeoutSeconds": 30
  },
  "NewRelic": {
    "LicenseKey": "",
    "ServiceName": "FBS-API",
    "OtlpEndpoint": "https://otlp.eu01.nr-data.net:4318"
  }
}

FBS.Function.Notifications — `local.settings.json`

{
  "IsEncrypted": false,
  "Values": {
    "AzureWebJobsStorage": "UseDevelopmentStorage=true",
    "FUNCTIONS_WORKER_RUNTIME": "dotnet-isolated",
    "ServiceBusConnection__fullyQualifiedNamespace": "fbs-servicebus-dev.servicebus.windows.net",
    "MailtrapApi__ApiToken": "YOUR_TOKEN",
    "MailtrapApi__InboxId": "YOUR_INBOX_ID",
    "MailtrapApi__FromEmail": "noreply@flightbooking.com",
    "MailtrapApi__FromName": "Flight Booking System"
  }
}

FBS.Function.ExpiredReservations — `local.settings.json`

{
  "IsEncrypted": false,
  "Values": {
    "AzureWebJobsStorage": "UseDevelopmentStorage=true",
    "FUNCTIONS_WORKER_RUNTIME": "dotnet-isolated",
    "ServiceBus__FullyQualifiedNamespace": "fbs-servicebus-dev.servicebus.windows.net",
    "ServiceBus__QueueName": "reservation-events",
    "EventPublisher__BaseUrl": "https://placeholder.local",
    "EventPublisher__RetryCount": "3",
    "EventPublisher__TimeoutSeconds": "30"
  },
  "ConnectionStrings": {
    "DefaultConnection": "Server=(localdb)\\mssqllocaldb;Database=FBS_Dev;Trusted_Connection=True;"
  }
}

🔄 CI/CD

Four GitHub Actions workflows with OIDC Workload Identity Federation (no client secrets):

Workflow	Trigger	What it does
`01-infrastructure.yml`	Push to `infra/**` or manual	Deploys Bicep — validates then applies Incremental
`02-deploy-api.yml`	Push to `src/FBS.API/**` or shared layers	Build → Publish → Configure App Settings → Deploy → Health check
`03-deploy-notifications.yml`	Push to `src/FBS.Function.Notifications/**`	Build → Publish → Zip → Configure App Settings → Zip Deploy
`04-deploy-expire.yml`	Push to `src/FBS.Function.ExpiredReservations/**`	Build → Publish → Zip → Configure App Settings → Zip Deploy

Required GitHub Secrets

Secret	Used in
`AZURE_CLIENT_ID`	All workflows (OIDC)
`AZURE_TENANT_ID`	All workflows (OIDC)
`AZURE_SUBSCRIPTION_ID`	All workflows (OIDC)
`SQL_CONNECTION_STRING`	`02`, `04`
`MAILTRAP_API_TOKEN`	`03`
`MAILTRAP_INBOX_ID`	`03`
`NEW_RELIC_LICENSE_KEY`	`02`, `03`, `04`

📊 Monitoring

Application Insights

Shared across all three applications. Filter by cloud_RoleName in Log Analytics:

traces
| where cloud_RoleName == "fbs-dev"
| order by timestamp desc

New Relic APM

FBS.API (Linux) — OpenTelemetry OTLP integration:

Distributed traces for all HTTP requests and outbound HttpClient calls
Configurable via NewRelic:* app settings
Skips /health endpoint to reduce noise

FBS.Function.Notifications / FBS.Function.ExpiredReservations (Windows) — Native New Relic .NET Agent via NewRelic.Agent NuGet package:

Auto-instruments Service Bus message processing, HTTP, async workflows
Configured via NEW_RELIC_* environment variables + CORECLR_* profiler settings

All three services appear under APM & Services in New Relic UI.

📄 License

This project is licensed under the MIT License.

🔗 Links

Repository: github.com/komenday/flight-booking-system
Live API: fbs-dev.azurewebsites.net/swagger

Name		Name	Last commit message	Last commit date
Latest commit History 31 Commits
.github/workflows		.github/workflows
infra		infra
postman		postman
scripts		scripts
src		src
.gitignore		.gitignore
Directory.Build.props		Directory.Build.props
FBS.sln		FBS.sln
README.md		README.md

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✈️ Flight Booking System (FBS)

📋 Table of Contents

🔍 Overview

Core Features

🏗️ Architecture

Clean Architecture Layers

Key Patterns

☁️ Azure Infrastructure

Managed Identity RBAC

🛠️ Technologies

Core

Azure & Cloud

Observability & DevOps

Libraries

📁 Project Structure

🔌 API Endpoints

Flights

Reservations

Example: Create Reservation

🎯 Domain Model

Aggregates

Event Flow

🚀 Getting Started

Prerequisites

Local Setup

Database Migrations

⚙️ Configuration

FBS.API — appsettings.json

FBS.Function.Notifications — local.settings.json

FBS.Function.ExpiredReservations — local.settings.json

🔄 CI/CD

Required GitHub Secrets

📊 Monitoring

Application Insights

New Relic APM

📄 License

🔗 Links

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FBS.API — `appsettings.json`

FBS.Function.Notifications — `local.settings.json`

FBS.Function.ExpiredReservations — `local.settings.json`

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