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Azure Functions Proxies: URL Rewriting and API Composition

Introduction

Azure Functions Proxies are a powerful feature that allows you to define proxies to control the behavior of HTTP requests and responses to and from your Azure Functions. You can use them for URL rewriting, request/response transformation, and API composition. Here are the steps to use Azure Functions Proxies in an ASP.NET Core application:

Create an Azure Functions Project

Start by creating an Azure Functions project in Visual Studio or using the Azure Functions Core Tools.

Define Your Azure Function

Define one or more Azure Functions that you want to expose via proxies. You can use the following code as an example.

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

Author: Sardar Mudassar Ali Khan
public static class AzureFunction
{
    [FunctionName("AzureFunction")]
    public static async Task<IActionResult> Run(
        [HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = "myfunction")] HttpRequest req,
        ILogger log)
    {
        // Your function logic here
        log.LogInformation("C# HTTP trigger function processed a request.");
        return new OkObjectResult("Hello from MyFunction!");
    }
}

Configure Azure Functions Proxies

In your proxies.json file, you can configure URL rewriting, request/response transformation, and API composition. Here's an example proxies.json configuration that demonstrates these capabilities.

Author: Sardar Mudassar Ali Khan
{
  "$schema": "http://json.schemastore.org/proxies",
  "proxies": {
    "rewriteExample": {
      "matchCondition": {
        "route": "/api/{*restOfPath}"
      },
      "responseOverrides": {
        "response.statusCode": 200,
        "response.headers.content-type": "application/json"
      },
      "backendUri": "https://backend.azurewebsites.net/{restOfPath}",
      "methods": ["GET", "POST"]
    },
    "transformExample": {
      "matchCondition": {
        "methods": ["GET"],
        "route": "/api/data"
      },
      "backendUri": "https://dataapi.azurewebsites.net/api",
      "requestTransforms": [
        {
          "set": {
            "body": {
              "key1": "value1",
              "key2": "value2"
            }
          }
        }
      ],
      "responseTransforms": [
        {
          "set": {
            "body": {
              "transformedKey": "$.originalKey"
            }
          }
        }
      ]
    }
  }
}

In this example

  • rewriteExample rewrites requests to /api/{*restOfPath} and forwards them to a different backend.
  • transformExample transforms the request and response for requests to /api/data before forwarding them to another backend.

Deploy Your Azure Functions

Deploy your Azure Functions to Azure using your preferred deployment method, such as Azure DevOps, GitHub Actions, or the Azure portal.

Test the Proxies

  1. After deploying your Azure Functions, you can test the proxies by sending HTTP requests to the proxy endpoints defined in your proxies.json file. Ensure that the requests and responses match your configured rules.
  2. Azure Functions Proxies provide powerful capabilities for controlling the behavior of your APIs. You can use them to route requests, rewrite URLs, and transform data as needed for your application.


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