Next JS 9: Proxy middleware with Express

local-server.js

// local-server.js
const express = require('express');
const next = require('next');
const { createProxyMiddleware } = require('http-proxy-middleware');

const conf = require('./next.config');

const dev = process.env.NODE_ENV !== 'production';
const port = parseInt(process.env.PORT, 10) || 3000;

const app = next({ dev, conf });
const handler = app.getRequestHandler();

const devProxy = {
  [`/${process.env.API_PATH}`]: {
    target: process.env.BACKEND_API,
    pathRewrite: {
      [`^/${process.env.API_PATH}`] : '',
    },
    changeOrigin: true,
  }
};

app.prepare().then(() => {
  const server = express();

  // Set up the proxy.
  if (dev && devProxy) {
    Object.keys(devProxy).forEach(context => {
      server.use(createProxyMiddleware(context, devProxy[context]))
    })
  }

  server.all('*', (req, res) => handler(req, res))

  server.listen(port, (err) => {
    if (err) throw err
    console.info(`🚀 Ready on http://localhost:${port}`);
  })
})

next.config

// next.config
module.exports = {
  api: {
    externalResolver: true,
  },
}