CQRS Pattern on Azure

This repository implements the CQRS (Command Query Responsibility Segregation) Pattern using Azure services, including Azure Functions, Azure Cosmos DB, and Azure Event Hubs. The CQRS Pattern separates read and write operations for a data store, optimizing them independently for performance and scalability.

🏗️ Architectural Overview

The CQRS Pattern architecture consists of the following components:

App Service API: Acts as the main entry point for both command and query operations.
Command Handler Function: Handles data insertion (command) operations and publishes events to Azure Event Hubs.
Update Processor Function: Listens to events from Azure Event Hubs and updates the Command DB.
Query Handler Function: Handles data retrieval (query) operations by accessing the Query DB.
Azure Event Hubs: Serves as the event streaming platform for processing events.
Azure Cosmos DB: Used for both command (write) and query (read) operations.

📊 Architectural Diagram

graph TD
    Client["Client"] -->|Insert Data| CommandHandler["Command Handler (Azure Function)"]
    CommandHandler -->|Insert| CommandDB["Command DB (Azure Cosmos DB)"]
    CommandHandler -->|Publish Event| EventHub["Azure Event Hubs"]
    EventHub -->|Trigger| UpdateProcessor["Update Processor (Azure Function)"]
    UpdateProcessor -->|Update Data| CommandDB
    UpdateProcessor -->|Update Data| QueryDB["Query DB (Azure Cosmos DB)"]
    Client -->|Query Data| QueryHandler["Query Handler (Azure Function)"]
    QueryHandler -->|Read| QueryDB

    subgraph Monitoring
        AppInsights["Application Insights"]
    end

    CommandHandler -->|Logs & Telemetry| AppInsights
    UpdateProcessor -->|Logs & Telemetry| AppInsights
    QueryHandler -->|Logs & Telemetry| AppInsights
    apiAppService["App Service API"] -->|Logs & Telemetry| AppInsights
    Client -->|Send Requests| apiAppService
    apiAppService -->|Insert Data / Query Data| CommandHandler
    apiAppService -->|Insert Data / Query Data| QueryHandler

📂 Repository Structure

/cqrs-pattern
│
├── README.md                                # Root README with architecture overview and getting started
├── LICENSE                                  # MIT License
│
├── infrastructure
│   ├── README.md                            # README for Infrastructure deployment
│   ├── azure-resources.bicep                # Bicep template for all Azure resources
│   └── .github/workflows/deploy-bicep.yml   # GitHub Action to deploy Azure resources
│
├── app-service-api
│   ├── README.md                            # README for App Service API
│   ├── Program.cs                           # C# code for App Service API
│   ├── appsettings.json                     # App settings for API configuration
│   └── .github/workflows/deploy-api.yml     # GitHub Action to deploy App Service API
│
├── command-handler
│   ├── README.md                            # README for Command Handler Function
│   ├── CommandHandler.cs                    # C# code for Command Handler Function
│   └── .github/workflows/deploy-command-handler.yml # GitHub Action to deploy Command Handler Function
│
├── update-processor
│   ├── README.md                            # README for Update Processor Function
│   ├── UpdateProcessor.cs                   # C# code for Update Processor Function
│   └── .github/workflows/deploy-update-processor.yml # GitHub Action to deploy Update Processor Function
│
├── query-handler
│   ├── README.md                            # README for Query Handler Function
│   ├── QueryHandler.cs                      # C# code for Query Handler Function
│   └── .github/workflows/deploy-query-handler.yml # GitHub Action to deploy Query Handler Function

🚀 Getting Started

Step 1: Deploy the Infrastructure

Navigate to the infrastructure folder.
Follow the instructions in the Infrastructure README to deploy the required Azure resources using the Bicep template and GitHub Actions.

Step 2: Deploy the Azure Functions and App Service API

Deploy the Command Handler Function:
- Navigate to the command-handler folder.
- Follow the instructions in the Command Handler Function README to deploy the function using GitHub Actions.
Deploy the Update Processor Function:
- Navigate to the update-processor folder.
- Follow the instructions in the Update Processor Function README to deploy the function using GitHub Actions.
Deploy the Query Handler Function:
- Navigate to the query-handler folder.
- Follow the instructions in the Query Handler Function README to deploy the function using GitHub Actions.
Deploy the App Service API:
- Navigate to the app-service-api folder.
- Follow the instructions in the App Service API README to deploy the API using GitHub Actions.
📊 Monitoring and Logging with Application Insights

This repository uses Azure Application Insights to monitor and collect telemetry data from all the Azure Functions and the App Service API. Application Insights helps to:

Track request rates, response times, and failure rates.
Monitor the performance of each service.
Diagnose failures and exceptions.
Gain insights into the usage patterns and overall health of the system.

How to View Application Insights Data

Go to the Azure Portal.
Navigate to Application Insights and select the cqrsAppInsights resource.
Use the available tools to explore logs, requests, failures, dependencies, and custom metrics.

By using Application Insights, you can maintain visibility into the operational status and performance of your CQRS architecture on Azure.

💡 How It Works

Insert Data:
- The Command Handler Function handles data insert operations and publishes events to Azure Event Hubs.
- The Update Processor Function listens to these events and updates the Command DB.
Query Data:
- The Query Handler Function handles data retrieval (query) operations from the Query DB.

📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

🙌 Contributing

Contributions are welcome! Please open an issue or submit a pull request for any improvements or suggestions.

error505/CQRS-Pattern-Azure