How to Build Serverless APIs with Azure Functions in Azure Portal

Azure Functions is a serverless compute service that allows us to run event-driven code without having to manage infrastructure. It enables developers to focus on business logic while Azure handles scaling, maintenance, and security. This article walks you through creating and deploying a serverless API using Azure Functions in the Azure Portal.

Why Use Azure Functions for APIs?

• Scalability: Automatically scales based on demand.
• Cost-Effective: Pay only for execution time.
• Easy Integration: It works seamlessly with other Azure services.
• Event-Driven: Trigger functions from HTTP requests, messages, or database changes.

Prerequisites

Before you begin, ensure you have,

• An Azure Subscription
• Azure Portal access to create and manage resources.
• Basic knowledge of C# or JavaScript (optional but helpful).

Step 1. Create an Azure Function App.

• Sign in to the Azure Portal.
• Click Create a resource and search for Function App.
  
• Click Create and fill in the required details.
  • Subscription: Select your Azure subscription.
  • Resource Group: Create a new one or use an existing one.
  • Function App name: Enter a unique name.
  • Runtime Stack: Choose .NET, Node.js, Python, or Java.
  • Region: Select a region close to your users.
• Click Review + Create, then Create.
  

Step 2. Create a Serverless API with HTTP Trigger.

• Navigate to your Function App in the Azure Portal.
• Click Functions in the left menu and then + Create.
• Select HTTP trigger as the function template.
• Provide a function name and choose the Authorization level:
  • Anonymous: No authentication required.
  • Function: Requires a function key.
  • Admin: Requires an admin key.
• Click Create.
  

Step 3. Write and Test the Function.

• Open your newly created function and click Code + Test.
• Modify the default code (C# example)

  using System.IO;
  using Microsoft.AspNetCore.Mvc;
  using Microsoft.Azure.WebJobs;
  using Microsoft.Azure.WebJobs.Extensions.Http;
  using Microsoft.AspNetCore.Http;
  using Newtonsoft.Json;
  using System.Threading.Tasks;
  
  public static class MyFunction
  {
      [FunctionName("MyFunction")]
      public static async Task<IActionResult> Run(
          [HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)] HttpRequest req)
      {
          string name = req.Query["name"];
  
          string requestBody = await new StreamReader(req.Body).ReadToEndAsync();
          dynamic data = JsonConvert.DeserializeObject(requestBody);
          name = name ?? data?.name;
  
          return name != null
              ? new OkObjectResult($"Hello, {name}!")
              : new BadRequestObjectResult("Please pass a name in the query string or in the request body.");
      }
  }
  

• Click Test/Run, enter a query parameter (?name=Azure), and check the response.

Step 4. Deploy and Expose the API.

• Click Get Function URL and copy the generated URL.
• Test the API using Postman or a browser.
• https://<function-app-name>.azurewebsites.net/api/MyFunction?name=Azure
• (Optional) Secure the API using Azure API Management or Azure Active Directory (AAD).

Step 5. Monitor and Scale.

• Navigate to Monitor in the function app to check logs and analytics.
• Enable Application Insights for detailed telemetry.
• Set scaling options based on usage patterns.

Conclusion

Azure Functions provide a fast, scalable, and cost-efficient way to build APIs without managing servers. By following this guide, you have successfully created and deployed a serverless API using Azure Functions. Explore additional triggers like Azure Storage, Service Bus, and Event Grid to expand your API capabilities.