LeaveFlow — Vacation Management System

A production-ready, microservices-based Vacation Management System built with .NET 10, React + TypeScript, and PostgreSQL. Designed with Clean Architecture, CQRS, and role-based access control.

This project was developed based on a Full-Stack technical assessment that required building an internal Vacation Management System with role-based permissions, vacation overlap validation, and proper business rule enforcement.

While the original exercise focused on delivering a functional full-stack solution, this implementation expands the scope into a production-oriented architecture, applying microservices, Clean Architecture, CQRS, JWT authentication, Docker, and enterprise-level best practices.

---

Architecture

┌──────────────┐
│ Frontend │ React + TypeScript + Vite
│ (port 3000) │
└──────┬───────┘
│
┌──────▼───────┐
│ API Gateway │ YARP Reverse Proxy
│ (port 5000) │
└──┬───┬───┬───┘
│ │ │
┌──▼┐ ┌▼──┐ ┌▼────────┐
│ID │ │EMP│ │VACATION │ Microservices
│5101│ │5102│ │5103 │ ASP.NET Core
└──┬┘ └─┬─┘ └──┬──────┘
│ │ │
┌──▼────▼──────▼───┐
│ PostgreSQL │ 3 isolated databases
│ (port 5432) │
└──────────────────┘

Each service follows Clean Architecture:

Service/
├── Domain/ # Entities, interfaces, business rules
├── Application/ # CQRS commands/queries, validators, mapping
├── Infrastructure/ # EF Core, repositories, persistence
└── API/ # Controllers, middleware, configuration

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Tech Stack

Component	Technology
Backend	.NET 10, ASP.NET Core Web API
Frontend	React 19, TypeScript, Vite
Database	PostgreSQL 16
ORM	Entity Framework Core 10
Gateway	YARP Reverse Proxy
Auth	JWT Bearer Tokens
CQRS	MediatR 12
Validation	FluentValidation
Mapping	AutoMapper
Logging	Serilog
Docs	Swagger / OpenAPI
Containers	Docker + Docker Compose
State Mgmt	Zustand

---

Microservices

Service	Port	Responsibility
API Gateway	5000	Routes requests to downstream services
Identity Service	5101	Authentication, JWT token generation
Employee Service	5102	Employee CRUD, role management
Vacation Service	5103	Vacation requests, overlap validation, approvals

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Business Rules

• Roles: Admin, Manager, Collaborator
• Admin: Full access — manages all employees and vacation requests
• Manager: Approves/rejects requests for their team
• Collaborator: Can only view/create their own vacation requests
• Overlap Rule: No two employees can have overlapping vacation dates (validated at domain + database level)
• Statuses: Pending → Approved / Rejected / Cancelled

---

Quick Start with Docker

# Clone the repository
git clone https://github.com/Remisu/LeaveFlow.git
cd LeaveFlow
# Start all services
docker-compose up --build
# Access the application# Frontend: http://localhost:3000# Gateway: http://localhost:5000# Identity: http://localhost:5101/swagger# Employee: http://localhost:5102/swagger# Vacation: http://localhost:5103/swagger

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Running Without Docker

Prerequisites

• .NET 10 SDK
• Node.js 20+
• PostgreSQL 16+

1. Create Databases

CREATEDATABASEleaveflow_identity;
CREATEDATABASEleaveflow_employee;
CREATEDATABASEleaveflow_vacation;

2. Start Backend Services

# Terminal 1 — Identity Servicecd src/Services/Identity/LeaveFlow.Identity.API
dotnet run --urls=http://localhost:5101
# Terminal 2 — Employee Servicecd src/Services/Employee/LeaveFlow.Employee.API
dotnet run --urls=http://localhost:5102
# Terminal 3 — Vacation Servicecd src/Services/Vacation/LeaveFlow.Vacation.API
dotnet run --urls=http://localhost:5103
# Terminal 4 — API Gatewaycd src/ApiGateway/LeaveFlow.ApiGateway
dotnet run --urls=http://localhost:5000

3. Start Frontend

cd src/Frontend/leaveflow-ui
npm install
npm run dev

Open http://localhost:3000

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Default Credentials

Role	Email	Password
Admin	admin@leaveflow.com	Admin@123
Manager	manager@leaveflow.com	Manager@123
Collaborator	john@leaveflow.com	Collab@123
Collaborator	alice@leaveflow.com	Collab@123

---

API Documentation

Each service exposes Swagger UI:

• Identity: http://localhost:5101/swagger
• Employee: http://localhost:5102/swagger
• Vacation: http://localhost:5103/swagger

Key Endpoints

POST /api/auth/login — Authenticate and get JWT token
GET /api/employees — List employees (paginated)
POST /api/employees — Create employee (Admin only)
PUT /api/employees/{id} — Update employee (Admin only)
DELETE /api/employees/{id} — Delete employee (Admin only)
GET /api/vacations — List vacation requests (paginated)
POST /api/vacations — Create vacation request
PUT /api/vacations/{id} — Update vacation request
POST /api/vacations/{id}/review — Approve/reject (Manager/Admin)
POST /api/vacations/{id}/cancel — Cancel own request
GET /api/vacations/calendar — Calendar view data

---

Testing the Overlap Rule

1. Login as john@leaveflow.com
2. Create a vacation request for July 1–5
3. Login as alice@leaveflow.com
4. Try to create a vacation request for July 3–7
5. You should receive a 409 Conflict response:

{
"statusCode": 409,
"message": "The requested vacation dates overlap with an existing approved or pending vacation request."
}

The overlap check validates:

• At the domain layer via VacationRequest.OverlapsWith()
• At the database layer via HasOverlappingVacationAsync()
• At the service layer in command handlers before persisting

---

Views and UI

Page	Description
Login	Clean authentication form with credential hints
Dashboard	Statistics cards showing request counts
Employees	Admin-only CRUD table with pagination
Vacations	Request list with create/cancel actions
Approvals	Pending requests with approve/reject workflow
Calendar	Monthly view with color-coded vacation blocks

---

Project Structure

LeaveFlow/
├── docker-compose.yml
├── Directory.Build.props
├── LeaveFlow.sln
├── README.md
├── scripts/
│ └── init-databases.sql
├── src/
│ ├── ApiGateway/
│ │ └── LeaveFlow.ApiGateway/
│ ├── BuildingBlocks/
│ │ └── LeaveFlow.Shared/ # DTOs, Enums, Exceptions
│ ├── Services/
│ │ ├── Identity/
│ │ │ ├── LeaveFlow.Identity.Domain/
│ │ │ ├── LeaveFlow.Identity.Application/
│ │ │ ├── LeaveFlow.Identity.Infrastructure/
│ │ │ └── LeaveFlow.Identity.API/
│ │ ├── Employee/
│ │ │ ├── LeaveFlow.Employee.Domain/
│ │ │ ├── LeaveFlow.Employee.Application/
│ │ │ ├── LeaveFlow.Employee.Infrastructure/
│ │ │ └── LeaveFlow.Employee.API/
│ │ └── Vacation/
│ │ ├── LeaveFlow.Vacation.Domain/
│ │ ├── LeaveFlow.Vacation.Application/
│ │ ├── LeaveFlow.Vacation.Infrastructure/
│ │ └── LeaveFlow.Vacation.API/
│ └── Frontend/
│ └── leaveflow-ui/ # React + TypeScript + Vite

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Future Improvements

• Email notifications for request status changes
• Vacation balance / annual allowance tracking
• Team calendar with manager-level filtering
• RabbitMQ / Azure Service Bus for inter-service messaging
• Redis caching layer
• Rate limiting on the API Gateway
• Health checks and readiness probes
• Unit and integration test projects
• CI/CD pipeline (GitHub Actions)
• Kubernetes deployment manifests
• Audit trail / event sourcing

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License

This project is open source and available under the MIT License.