MQTT Broker - Clean Architecture

Overview

Mqtt-Broker is an MQTT broker built on top of MQTTnet with a focus on IoT device management and Clean Architecture. It provides:

• Per-device subscriptions (event/{chipId})
• One-to-one and group event delivery
• Modular event handling strategies
• Database as source-of-truth for devices and groups
• Seamless .NET integration with DI, middleware, and REST APIs

---

Architecture

Main Layers

• Presentation: Controllers, middleware, REST endpoints.
• Application: Use cases, application services, AutoMapper profiles.
• Domain: Core business entities and logic.
• Infrastructure: MQTT, Redis, logging, etc.
• Persistence: Repositories, data contexts, UnitOfWork.
• Shared: DTOs, requests/responses, enums, utilities.
• Extensions: Configuration and service wiring helpers.

---

MQTT Event Flow

1. Client Connection: MQTT service connects to the broker and subscribes to event/{chipId} for managed devices.
2. Device Registration: Device sends a Status event on connection. Backend registers or updates the device in the database.
3. Individual Event Delivery: Backend publishes to event/{chipId}.
4. Group Event Delivery: Backend queries DB for group members and publishes individually. Redis serves as cache/helper.

---

Event Strategies

• StatusStrategy: Handles device registration and status updates.
• TelemetryStrategy: Processes telemetry data from devices.
• ErrorUpdateFirmwareDeviceStrategy: Logs errors during firmware updates.

---

Message Structures

MqttRequest – from device to backend:

{
  "Device": { "ChipId": "CHIP-12345", "Name": "Sensor-01", "FirmwareVersion": "1.2.3" },
  "Timestamp": "2025-12-03T12:00:00Z",
  "Details": { "temperature": 22.4 }
}

MqttResponse – from backend to device:

{
  "EventType": "UPDATE_FIRMWARE",
  "Timestamp": "2025-12-03T12:05:00Z",
  "Details": { "version": "2.0.0", "url": "https://example.com/firmware.bin" }
}

---

Device DTO

DeviceDto fields:

• Id, ChipId, ChipType, Name, Code, MacAddress, FirmwareVersion, Status, GroupName, GroupDescription, Description, ErrMessage

These structures support device status updates (MqttRequest) and backend commands/events (MqttResponse).

---

Redis Configuration (Development)

Two Redis instances recommended:

• redis-aof – persistent (appendonly yes)
• redis-noaof – in-memory (appendonly no)

Docker Run Example:

docker run -d --name redis-aof -p 6379:6379 redis:7 redis-server --appendonly yes
docker run -d --name redis-noaof -p 6380:6380 redis:7 redis-server --appendonly no

Docker Compose Example:

version: '3.8'
services:
  redis-aof:
    image: redis:7
    command: ["redis-server", "--appendonly", "yes"]
    ports: ["6379:6379"]

  redis-noaof:
    image: redis:7
    command: ["redis-server", "--appendonly", "no"]
    ports: ["6380:6380"]

---

Running the Project (Windows / PowerShell)

dotnet restore "Mqtt-Broker.sln"
dotnet build "Mqtt-Broker.sln" -c Debug
# Start Redis instances
docker-compose -f docker-compose.redis.yml up -d
# Run application
dotnet run --project "Mqtt-Broker\Mqtt-Broker.csproj" -c Debug

---

MQTT Topics & Event Routing

• Device topic: event/{chipId}
• Group topic: Optional group/{groupId}
• Event type mapping: Last segment of topic → MqttEventType (case-insensitive)

Registered Event Types:

• Status → /status
• Telemetry → /telemetry
• ErrorUpdateFirmwareDevice → /ErrorUpdateFirmwareDevice

Status Event Flow:

1. Device subscribes to event/{chipId}
2. Publishes Status message → backend maps topic segment → routes to StatusStrategy
3. StatusStrategy creates/updates device in DB and marks as online

---

Microcontroller Notes (ESP32/ESP8266)

• Use MQTTOTA as reference for OTA updates.
• Device subscribes to event/{chipId} and optionally group/{groupName}.
• Sends Status events to register in backend.
• Handles incoming MqttResponse<TDetails> messages for firmware updates, commands, etc.

---

API Keys, Middleware & Responses

• API keys for MQTT endpoints in appsettings.json

• Middleware handles:

  • Exception handling
  • Logging
  • CORS
  • API key validation
  • Standard response wrapper (BaseResponse)

BaseResponse:

• Message – string
• StatusCode – HTTP status
• Details – optional payload
• Pagination – optional metadata

---

Security Notes

• Keep API keys secret; rotate regularly
• Production: prefer OAuth2/JWT over static keys

---

Contact / Development

• Email: chinausto@gmail.com
• Main project file: Mqtt-Broker/Mqtt-Broker.csproj
• Config: appsettings.json / appsettings.Development.json

---