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Use Dev Proxy with JavaScript Azure Functions

If you build Azure Functions using JavaScript and want to use Dev Proxy, follow the general guidance for using Dev Proxy with Node.js 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. Additionally, disable certificate validation to allow the Azure Functions app to trust the self-signed certificate used by Dev Proxy.

{
  "IsEncrypted": false,
  "Values": {
    "FUNCTIONS_WORKER_RUNTIME": "node",
    "AzureWebJobsFeatureFlags": "EnableWorkerIndexing",
    "AzureWebJobsStorage": "UseDevelopmentStorage=true",
    "HTTPS_PROXY": "http://127.0.0.1:8000",
    "NODE_TLS_REJECT_UNAUTHORIZED": "0"
  }
}

In your Azure Functions app, use the process.env object to read the environment variables and configure the proxy for your HTTP requests.

import { app, HttpRequest, HttpResponseInit, InvocationContext } from "@azure/functions";
import fetch from 'node-fetch';
import { HttpsProxyAgent } from 'https-proxy-agent';

export async function MyFnHttpTrigger(request: HttpRequest, context: InvocationContext): Promise<HttpResponseInit> {
    const options = process.env.HTTPS_PROXY ? { agent: new HttpsProxyAgent(process.env.HTTPS_PROXY) } : {};
    const resp = await fetch('https://jsonplaceholder.typicode.com/posts', options);
    const data = await resp.json();
    return {
      status: 200,
      jsonBody: data
    };
};

app.http('MyFnHttpTrigger', {
    methods: ['GET', 'POST'],
    authLevel: 'anonymous',
    handler: MyFnHttpTrigger
});