Azure Functions custom handler example

This is a simple example of an Azure Functions custom handler written in C#. Of course, Azure Functions supports C# quite nicely out-of-the-box, so typically there's no need for this if you're targeting C#. However, there are scenarios where you might want to leverage the Azure Functions host model (elastic scale, triggers and bindings, consumption-based pricing, etc.) but use a different programming model than functions-as-a-service.

Custom handlers run as a standalone HTTP endpoint adjacent to the Functions runtime, and invoked by the Functions runtime in response to Functions input:

This sample implements the handler as a standard ASP.NET Core Web API app. The Functions runtime and Web API app are baked into a single Docker image which runs equally well on your laptop or in the cloud.

Pre-requisites

• Docker Desktop

• Powershell

• Postman or some other API testing tool

Build and run

• clone the repo

• open a Powershell prompt in the FunctionHost folder

• execute the build-and-run.ps1 script, which will:

  • delete any existing 'bin' and 'obj' folders
  • copy all source from WebApplication1 to 'FunctionHost/src'
  • build a Docker image to host the Functions runtime and your custom ASP.NET endpoint (invoked by the Functions runtime) using this Dockerfile
  • start up a container using the image built in the last step

• to interact with the Functions app, use Postman or a similar tool to issue an HTTP GET:

http://localhost:5002/api/test/some-value