Creating Custom Triggers for Azure Functions with Azure Event Hubs and Azure Service Bus

Azure Functions is a serverless compute service that allows you to run your code on-demand without having to manage infrastructure. With Azure Functions, you can build scalable, event-driven applications that can respond to changes in real-time. One way to achieve this is by creating custom triggers that respond to events from Azure Event Hubs and Azure Service Bus. In this tutorial, we'll show you how to create custom triggers for Azure Functions using these two services.

Prerequisites

Before we get started, you'll need to have the following:

1. An Azure account

2. Visual Studio Code

3. Azure Functions extension for Visual Studio Code

Creating an Azure Event Hub 

The first step is to create an Azure Event Hub. In the Azure portal, select "Create a resource" and search for "Event Hubs". Choose "Event Hubs" and follow the prompts to create a new Event Hub.

Once your Event Hub is created, you can send events to it using any compatible client library. In this tutorial, we'll use the Azure Functions extension for Visual Studio Code to create a custom trigger that responds to events from our Event Hub.

Creating an Azure Service Bus

The next step is to create an Azure Service Bus. In the Azure portal, select "Create a resource" and search for "Service Bus". Choose "Service Bus" and follow the prompts to create a new Service Bus.

Once your Service Bus is created, you can send messages to it using any compatible client library. We'll use the Azure Functions extension for Visual Studio Code to create a custom trigger that responds to messages from our Service Bus.

Creating Custom Triggers for Azure Functions

Now that our Event Hub and Service Bus are set up, we can create custom triggers for Azure Functions that respond to events and messages from these services.

To create a custom trigger for Azure Functions, you'll need to define a function that takes in the event or message as input. This function can then process the event or message and perform any necessary actions.

Custom Trigger for Azure Event Hubs

Here's an example of a custom trigger for Azure Event Hubs:

module.exports = async function(context, eventHubMessages) {

    context.log(`Event hub trigger function called for message array: ${eventHubMessages}`);

    eventHubMessages.forEach(message => {

        // Process message here

    });

};

This function takes in the eventHubMessages array as input and processes each message in the array. You can add your own processing logic to this function, such as sending notifications or updating a database.

To connect this function to your Event Hub, you'll need to add a new function to your Azure Functions app using the Event Hub trigger template. Follow the prompts to specify the Event Hub connection string and configure the function.

Custom Trigger for Azure Service Bus

Here's an example of a custom trigger for Azure Service Bus:

module.exports = async function(context, mySbMsg) {

    context.log(`Service bus trigger function called for message: ${mySbMsg}`);

    // Process message here

};

This function takes in the mySbMsg object as input and processes the message. You can add your own processing logic to this function, such as sending notifications or updating a database.

To connect this function to your Service Bus, you'll need to add a new function to your Azure Functions app using the Service Bus trigger template. Follow the prompts to specify the Service Bus connection string and configure the function.

Building a Serverless Web App with Azure Functions and Azure Cosmos DB

 Server less computing has revolutionized the way we build and deploy web applications. With server less, you can focus on writing code without worrying about managing infrastructure, and pay only for the compute resources you use. In this tutorial, we'll show you how to build a server less web app with Azure Functions and Azure Cosmos DB that provides scalable and cost-effective data storage and processing.

Prerequisites

Before we get started, you'll need to have the following:

1. An Azure account
2. Visual Studio Code
3. Azure Functions extension for Visual Studio Code
4. Azure Cosmos DB extension for Visual Studio Code

Creating the Azure Functions App

The first step is to create an Azure Functions app. In Visual Studio Code, select the Azure Functions extension and choose "Create New Project". Follow the prompts to choose your programming language and runtime.

Once your project is created, you can create a new function by selecting the "Create Function" button in the Azure Functions Explorer. Choose the HTTP trigger template to create a function that responds to HTTP requests.

In this example, we'll create a function that retrieves data from Azure Cosmos DB. We'll use the Cosmos DB extension for Visual Studio Code to connect to our database and retrieve data.

Creating the Azure Cosmos DB Account

Next, we'll create an Azure Cosmos DB account to store our data. In the Azure portal, select "Create a resource" and search for "Cosmos DB". Choose "Azure Cosmos DB" and follow the prompts to create a new account.

Once your account is created, select "Add Collection" to create a new container for your data. Choose a partition key and throughput level, and select "Create". You can now add data to your container through the Azure portal or through your Azure Functions app.

Connecting the Azure Functions App to Azure Cosmos DB

To connect your Azure Functions app to Azure Cosmos DB, you'll need to add the Cosmos DB extension to your project. In Visual Studio Code, select the Extensions icon and search for "Azure Cosmos DB". Install the extension and reload Visual Studio Code.

Next, open your function code and add the following code to your function:

const { CosmosClient } = require("@azure/cosmos");

module.exports = async function (context, req) {
    const endpoint = process.env["CosmosDBEndpoint"];
    const key = process.env["CosmosDBKey"];
    const client = new CosmosClient({ endpoint, key });
    
    const database = client.database("mydatabase");
    const container = database.container("mycontainer");
    
    const querySpec = {
        query: "SELECT * FROM c"
    };
    
    const { resources } = await container.items.query(querySpec).fetchAll();
    
    context.res = {
        body: resources
    };
}

This code connects to your Azure Cosmos DB account and retrieves all data from the specified container. Replace "mydatabase" and "mycontainer" with your database and container names.

Finally, add your Azure Cosmos DB account endpoint and key to your function's Application Settings. In the Azure Functions Explorer, select your function and choose "Application Settings". Add the following settings:

CosmosDBEndpoint: Your Azure Cosmos DB account endpoint
CosmosDBKey: Your Azure Cosmos DB account key

Conclusion

we learned how to build a serverless web app with Azure Functions and Azure Cosmos DB. We created an Azure Functions app and a new function that retrieves data from Azure Cosmos DB using the Cosmos DB extension for Visual Studio Code.

We also created an Azure Cosmos DB account and added a new container to store our data. Finally, we connected our Azure Functions app to Azure Cosmos DB by adding the necessary code and application settings. By using Azure Functions and Azure Cosmos DB together, you can build scalable and cost-effective web applications that handle data storage and processing without managing infrastructure.

You can extend this example to include more complex queries, data manipulation, and other functions that respond to HTTP requests or other triggers. 

 If you're new to serverless computing or Azure Functions, be sure to check out the documentation and resources available from Microsoft. With the right tools and knowledge, you can quickly build and deploy serverless web applications that are flexible, scalable, and cost-effective.