Building a Serverless API with Azure Functions

Introduction to Serverless APIs

Serverless computing, powered by Azure Functions, revolutionizes how we build and deploy APIs. It allows you to write and deploy code without managing infrastructure. Your code runs in response to events, and you only pay for the compute time you consume.

This tutorial will guide you through the essential steps of creating a basic serverless API using Azure Functions. We'll cover:

Setting up your development environment.
Creating your first Azure Function HTTP trigger.
Handling requests and responses.
Deploying your function to Azure.

Step 1: Setting Up Your Development Environment

Before you begin, ensure you have the following installed:

.NET SDK (version 6.0 or later)
Azure Functions Core Tools. You can install it globally using npm: npm install -g azure-functions-core-tools@4 --unsafe-perm true
Visual Studio Code with the Azure Functions extension is recommended for a seamless experience.

You can verify your installation by running:

func --version

Step 2: Creating Your First Azure Function

Let's create a new Azure Functions project.

Open your terminal or command prompt.
Navigate to the directory where you want to create your project.

Run the following command to create a new function app project:

func init MyServerlessApi --worker-runtime dotnet --language csharp

Navigate into the newly created project directory:
```
cd MyServerlessApi
```

Create a new HTTP-triggered function:

func new --template "Http trigger" --name HelloHttp

This command creates a new function named HelloHttp with an HTTP trigger. Open the project in your preferred IDE to explore the generated files.

Step 3: Understanding the Function Code

Open the HelloHttp.cs file. It will look something like this:


using System.IO;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.Http;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using Newtonsoft.Json;

namespace MyServerlessApi
{
    public static class HelloHttp
    {
        [FunctionName("HelloHttp")]
        public static async Task Run(
            [HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)] HttpRequest req,
            ILogger log)
        {
            log.LogInformation("C# HTTP trigger function processed a request.");

            string name = req.Query["name"];

            string requestBody = await new StreamReader(req.Body).ReadToEndAsync();
            dynamic data = JsonConvert.DeserializeObject(requestBody);
            name = name ?? data?.name;

            string responseMessage = string.IsNullOrEmpty(name)
                ? "This HTTP triggered function executed successfully. Pass a name in the query string or in the request body for a personalized response."
                : $"Hello, {name}!";

            return new OkObjectResult(responseMessage);
        }
    }
}

Key components:

[FunctionName("HelloHttp")]: Identifies the function name.
[HttpTrigger(...)]: Defines the trigger type and allowed HTTP methods (GET, POST). AuthorizationLevel.Anonymous means no API key is required.
HttpRequest req: Represents the incoming HTTP request.
ILogger log: Used for logging.
IActionResult: The return type, representing the HTTP response.

Step 4: Running Your Function Locally

To test your function without deploying, run the following command in your project's root directory:

func start

This will start a local Azure Functions host. You'll see output indicating the URL where your function is accessible, typically something like:

Http Functions:
HelloHttp - [GET,POST] http://localhost:7071/api/HelloHttp

Open your browser or use a tool like curl to send requests:

curl http://localhost:7071/api/HelloHttp?name=World

You should receive a response: Hello, World!

Step 5: Deploying to Azure

Deploying your function to Azure is straightforward with the Azure Functions Core Tools.

Ensure you are logged into your Azure account:
```
az login
```
Deploy your function app:
```
func azure functionapp publish YourFunctionAppName
```
Replace YourFunctionAppName with a unique name for your function app in Azure.

Once deployed, you can find the function's URL in the Azure portal or in the deployment output. You can then test it using tools like Postman or by navigating to the URL in your browser.

Next Steps

Congratulations! You've built and deployed your first serverless API. From here, you can explore:

Different Triggers: Explore Timer triggers, Queue triggers, and more.
Data Access: Learn to connect to Azure Cosmos DB, SQL Database, and other services.
Input and Output Bindings: Simplify integrations with other Azure services.
Monitoring and Logging: Use Application Insights to track performance and troubleshoot issues.