Develop an Azure Functions trigger to process a change feed

Azure Functions provides a serverless compute platform that allows you to easily run your code in response to various events. One of the supported triggers is the Azure Cosmos DB Change Feed, which enables you to process changes to your Cosmos DB data in real-time. In this article, we will explore how to develop an Azure Functions trigger to process a change feed using the Designing and Implementing Native Applications Using Microsoft Azure Cosmos DB exam guide as a reference.

Prerequisites

Before we begin, make sure you have a basic understanding of Azure Functions and Azure Cosmos DB. If you’re not familiar with these technologies, you can refer to the official Microsoft documentation for more information.

Creating an Azure Function with a Cosmos DB Trigger

To get started, let’s create an Azure Function with a Cosmos DB trigger:

1. In the Azure Portal, navigate to the Azure Cosmos DB account that you want to use and go to the “Data Explorer” tab.
2. Select the desired container and click on the “Settings” tab.
3. In the “Change Feed” section, enable the change feed and copy the “Host” and “Key” values.

Next, create a new Azure Function in your preferred development environment. You can use Visual Studio, Visual Studio Code, or the Azure portal’s built-in code editor. Choose the appropriate language for your function (C#, JavaScript, etc.) and create a new function with a Cosmos DB trigger.

Implementing the Function Code

Once you have created the Azure Function, you need to specify the input binding for the Cosmos DB trigger in the function code. This binding allows the function to receive the change feed data as input. Here’s an example in C#:

#r “Microsoft.Azure.Documents.Client”
#r “Newtonsoft.Json”

using System.Collections.Generic;
using Microsoft.Azure.Documents;
using Newtonsoft.Json;

public static void Run(IReadOnlyList documents, TraceWriter log)
{
foreach (var document in documents)
{
// Process the change feed document
log.Info($”Document ID: {document.Id}”);
log.Info($”Document content: {document.ToString()}”);
}
}

In the example above, the `Run` function is triggered whenever a change occurs in the Cosmos DB container specified in the binding. The function receives a list of `Document` objects representing the changed documents. You can customize the processing logic inside the `foreach` loop as per your requirements.

Don’t forget to add the necessary package references for the `Microsoft.Azure.Documents.Client` and `Newtonsoft.Json` libraries. You can either use the `#r` directives as shown in the example or include the NuGet packages in your project file.

Deploying and Monitoring the Azure Function

Once you have implemented the function code, you can publish and deploy your Azure Function to your Azure subscription, following the instructions provided in the official documentation.

With the Azure Function deployed, it will automatically start processing the change feed whenever a change occurs in the specified Cosmos DB container. You can monitor the function’s execution logs to see the processing results and troubleshoot any issues that may arise.

Conclusion

Azure Functions provides a convenient way to process change feed events in Azure Cosmos DB. By following the steps outlined in this article, you can develop an Azure Functions trigger to process a change feed and incorporate it into your application workflows. Make sure to refer to the official Microsoft documentation for more advanced scenarios and capabilities of Azure Functions and Azure Cosmos DB.