Developing Asynchronous Serverless Functions with ASP.NET Core Azure Functions
Tags: aspnet, aspdotnet, azure, azurefunctions
Published: 2023-09-05 06:57:12

**Azure **Functions allow you to run event-driven serverless code without managing infrastructure. Functions can be triggered by HTTP requests, schedules, database changes, file uploads, and more.

**ASP.NET Core** provides a streamlined way to build Azure Functions using C# and .NET. In this post, we'll look at how to develop asynchronous Azure Functions with ASP.NET Core.

Benefits of Serverless Functions
Some key benefits of using serverless functions:

- No infrastructure to manage - Azure handles resource provisioning and scaling
- Pay per execution pricing - Consume only the resources you need
- Event-driven scale - Functions scale seamlessly based on demand
- Faster development - No need to manage threading, connections, etc.

## Creating an ASP.NET Core Azure Function

Let's walk through creating a basic HTTP triggered function using the Azure Functions template in Visual Studio:

- Create a new Azure Functions project
- Select HTTP trigger template
- Modify Run method:

```csharp
public static async Task<IActionResult> Run(HttpRequest req)
{
  return new OkObjectResult("Hello World!"); 
}
```
This will return "Hello World!" when the function URL is accessed.

## Making Asynchronous Functions

To make our function asynchronous, we can use the async and await keywords:

```csharp
public static async Task<IActionResult> Run(HttpRequest req)  
{
  await Task.Delay(1000);
  return new OkObjectResult("Hello World!");
}
```
This delays the response by 1 second to simulate latency.

The Run method signature returns a Task, allowing it to run asynchronously.

## Accessing the Request and Response

We can access details about the HTTP request via the HttpRequest parameter:

```csharp
var name = req.Query["name"];

return new OkObjectResult($"Hello {name}!");
```
This reads the name query parameter and personalizes the response.

We can also construct the HTTP response by returning an IActionResult or setting HttpResponse.

## Function Triggers and Bindings

Functions can be triggered by timers, queues, other Azure services, and more. We can access the trigger payload via parameter binding:

```csharp
public static async Task Run(
  [QueueTrigger("messagequeue")] string message, 
  ILogger log)
{
  log.LogInformation(message);
}
```
This queue-triggered function processes queue messages.

Input and output bindings streamline accessing services like Blob Storage from the function.

## Dependency Injection

ASP.NET Core Dependency Injection allows injecting services into functions:

```csharp
public class MyFunction 
{
  private readonly ILogger<MyFunction> logger;

  public MyFunction(ILogger<MyFunction> logger)
  {
    this.logger = logger;
  }

  public async Task Run(...) {
    logger.LogInformation("Function processed request");
  }
}
```
The function class can now access the logger service via DI.

## Some key points:

- ASP.NET Core is a great fit for writing Azure Functions with .NET
- Support for async/await provides efficient asynchronous code
- Triggers and bindings simplify connecting to other services
- Built-in features like DI enable loosely coupled functions
With Azure Functions and ASP.NET Core, you can quickly build scalable event-driven apps without managing servers. Learn about the [Common Architectures in ASP.NET Core](https://positiwise.com/blog/common-architectures-in-asp-net-core) in detail.