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🧭 Microservices Gateway with Ocelot and Swagger (.NET 9)

This solution demonstrates a simple API Gateway built with Ocelot that routes traffic to two downstream microservices:

• AuthService — handles authentication and issues JWT tokens.
• DataService — exposes example data endpoints.

The gateway also aggregates both services’ Swagger documentation using SwaggerForOcelot, providing a unified API explorer at a single URL.

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🚀 Tech Stack

Component	Purpose
.NET 9	Framework for all services
Ocelot	API Gateway / Reverse Proxy
MMLib.SwaggerForOcelot	Aggregates Swagger from downstream services
Swashbuckle.AspNetCore	Swagger UI for microservices
JWT Bearer Auth	Token-based authentication (AuthService)

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🏗️ Architecture Overview

┌─────────────────────────────┐
│        API Gateway          │
│ (Ocelot + SwaggerForOcelot) │
│       Port: 5123            │
└───────┬───────────┬─────────┘
        │           │
        ▼           ▼
┌─────────────────────────────┐    ┌─────────────────────────────┐
│        AuthService          │    │         DataService          │
│  Issues JWT tokens          │    │  Returns product data        │
│  Port: 5138                 │    │  Port: 5146                 │
└─────────────────────────────┘    └─────────────────────────────┘

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📂 Project Structure

MicroservicesOcelotDemo/
│
├── ApiGateway/
│   ├── Program.cs
│   ├── ocelot.json
│
├── AuthService/
│   ├── Program.cs
│
├── DataService/
│   ├── Program.cs
│
└── TestClient/
    └── Program.cs

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⚙️ Setup Instructions

1️⃣ Clone the Repository

git clone https://github.com/YOUR_USERNAME/MicroservicesOcelotDemo.git
cd MicroservicesOcelotDemo

2️⃣ Restore Dependencies

dotnet restore

3️⃣ Run Each Service in Separate Terminals

# Auth Service (port 5138)
cd AuthService
dotnet run --urls http://localhost:5138

# Data Service (port 5146)
cd DataService
dotnet run --urls http://localhost:5146

# API Gateway (port 5123)
cd ApiGateway
dotnet run --urls http://localhost:5123

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🌐 Access Points

URL	Description
http://localhost:5123/swagger	Aggregated Swagger (Auth + Data)
http://localhost:5123/auth/token	Token issuing endpoint (public)
http://localhost:5123/data/products	Data endpoint (example)
http://localhost:5138/swagger	AuthService Swagger
http://localhost:5146/swagger	DataService Swagger

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🧭 Gateway Routing Summary

Gateway Path	Forwards To	Description
/auth/*	http://localhost:5138/*	Auth endpoints
/data/*	http://localhost:5146/*	Data endpoints
/swagger	Aggregated docs	SwaggerForOcelot UI

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🧪 Testing

✅ Get a Token

curl -X POST http://localhost:5123/auth/token \
  -H "Content-Type: application/json" \
  -d '{ "username": "demo", "password": "demo" }'

✅ Access Protected Data

curl http://localhost:5123/data/products \
  -H "Authorization: Bearer YOUR_JWT_TOKEN"

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🧩 Key Configuration Files

ApiGateway/ocelot.json

{
  "Routes": [
    {
      "UpstreamPathTemplate": "/auth/{everything}",
      "UpstreamHttpMethod": [ "Get", "Post", "Put", "Delete", "Options" ],
      "DownstreamPathTemplate": "/{everything}",
      "DownstreamScheme": "http",
      "DownstreamHostAndPorts": [ { "Host": "localhost", "Port": 5138 } ]
    },
    {
      "UpstreamPathTemplate": "/data/{everything}",
      "UpstreamHttpMethod": [ "Get", "Post", "Put", "Delete", "Options" ],
      "DownstreamPathTemplate": "/{everything}",
      "DownstreamScheme": "http",
      "DownstreamHostAndPorts": [ { "Host": "localhost", "Port": 5146 } ]
    }
  ],
  "SwaggerEndPoints": [
    {
      "Key": "auth",
      "TransformByOcelotConfig": true,
      "Config": [
        { "Name": "Auth Service", "Version": "v1", "Url": "http://localhost:5138/swagger/v1/swagger.json" }
      ]
    },
    {
      "Key": "data",
      "TransformByOcelotConfig": true,
      "Config": [
        { "Name": "Data Service", "Version": "v1", "Url": "http://localhost:5146/swagger/v1/swagger.json" }
      ]
    }
  ],
  "GlobalConfiguration": { "BaseUrl": "http://localhost:5123" }
}

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💡 Notes

• The gateway is configured purely as a reverse proxy — no authentication required.
• Both microservices have independent Swagger UIs.
• The gateway’s Swagger aggregates both under /swagger.
• You can later enable JWT validation or rate limiting if needed.

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📦 NuGet Packages

Project	Package	Purpose
ApiGateway	Ocelot	Reverse proxy / API Gateway
ApiGateway	MMLib.SwaggerForOcelot.AspNetCore	Aggregates Swagger docs
AuthService	Swashbuckle.AspNetCore	Swagger UI
DataService	Swashbuckle.AspNetCore	Swagger UI
AuthService / DataService	Microsoft.AspNetCore.Authentication.JwtBearer	JWT auth

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📜 License

This project is licensed under the MIT License. Feel free to use, modify, and share.

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👤 Author

Spyros Ponaris 💼 LinkedIn