在 express 应用中配置代理中间件

Question

My application consists of a frontend server (React, serve as static) and backend server (Express). I found that whenever I am sending requests with custom headers, a preflight request will be sent. This increases the latency of my application. I would like to avoid those preflight requests.

For example,

frontend: example.web.com

backend: example.api.com

One approach found is to setup proxy middleware in my backend so that the requests will be sent from backend server to backend server instead of frontend (browser) to backend.

const proxy = require('http-proxy-middleware');
const express = require('express');
const cors = require('cors');

const app = express();
app.use(cors({
    origin: "*",
    methods: "GET,HEAD,PUT,PATCH,POST,DELETE",
    allowedHeaders: "authorization",
}));
let options = {
    target: 'http://localhost:5001/',
    changeOrigin: true,
    logLevel: 'debug',
    onError: function onError(err, req, res) {
        console.log('Something went wrong with the proxy middleware.', err)
        res.end();
    }
};
app.use("/", proxy(options), indexRouter);

What I expected to avoid preflight requests when sending not "simple" requests. I knew that proxy middleware approach can avoid preflight requests, but I do not know the right way to configure in my Express application.

Answer 1

http-proxy-middleware will send you the responses it gets from the target api server. it does not move on to the next middleware, though.

app.use("/", proxy(options)) means any request to your server will be proxied to the target api: a request to yourserver.com/items will be proxied to targetapi.com/items . If you want to be able to have your own routes, either use a prefix for the middleware ( app.use("/api", proxy(options)) ) or mount those other middlewares before the proxy.