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Use Dev Proxy with .NET Azure Functions

If you build Azure Functions using .NET and want to use Dev Proxy, follow the general guidance for using Dev Proxy with .NET applications.

Important

To prevent Azure Functions from failing on startup, start Dev Proxy without registering it as a system proxy either by using the --as-system-proxy false option or by configuring asSystemProxy to false in the devproxyrc.json file. If you register Dev Proxy as a system proxy, Azure Functions fails on startup with an error message similar to:

Grpc.Core.RpcException: 'Status(StatusCode="Internal", Detail="Error starting gRPC call. HttpRequestException: Requesting HTTP version 2.0 with version policy RequestVersionOrHigher while unable to establish HTTP/2 connection.", DebugException="System.Net.Http.HttpRequestException: Requesting HTTP version 2.0 with version policy RequestVersionOrHigher while unable to establish HTTP/2 connection.")'

To be able to easily switch between using Dev Proxy in development and not using it in production, you can best configure the proxy in your Azure Functions app using environment variables. Change the local.settings.json file to include the HTTPS_PROXY environment variable.

{
  "IsEncrypted": false,
  "Values": {
    "HTTPS_PROXY": "http://127.0.0.1:8000"
  }
}

HttpClient in .NET automatically picks up the HTTPS_PROXY environment variable and uses it to configure the proxy for outgoing HTTP requests.

using Microsoft.Azure.Functions.Worker;
using Microsoft.Extensions.Logging;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;

namespace dotnet_azure_fn;

public class MyFn(ILogger<MyFn> logger, IHttpClientFactory httpClientFactory)
{
    private readonly ILogger<MyFn> _logger = logger;
    private readonly HttpClient _httpClient = httpClientFactory.CreateClient();

    [Function("MyFn")]
    public async Task<IActionResult> Run([HttpTrigger(AuthorizationLevel.Anonymous, "get", "post")] HttpRequest req)
    {
        _logger.LogInformation("C# HTTP trigger function processed a request.");

        var result = await _httpClient.GetAsync("https://jsonplaceholder.typicode.com/posts");
        if (result.IsSuccessStatusCode)
        {
            return new OkObjectResult(await result.Content.ReadAsStringAsync());
        }
        else
        {
            _logger.LogError("HTTP request failed.");
            return new StatusCodeResult(StatusCodes.Status500InternalServerError);
        }
    }
}