CORS error when accessing NodeJS express api in Docker container

Question

I have NodeJS api and NextJS application in Separate docker containers when I'm in host machine its working fine, but when I'm running inside docker containers its giving CORS error.

My express config in API

app.use(cors({
    credentials: true,
    origin: 'http://localhost:3000/' // Allowing front-end running port 3000
}));

app.use(cookieParser());
app.use(bodyParser.json());
app.use(urlencoded({ extended: true }));
app.use(json());
app.enable("trust proxy");
app.use(methodOverride());

In front-end APP NextJS axios config

const axiosInstance = axios.create({ baseURL: 'http://localhost:4000/', withCredentials: true });

Its woking fine when im running API from host machine, with same configuration its giving CORS error in Docker.

Answer 1

As i can see your API configuration seems correct, but in your NextJS create pages/api/whatever.js and call your API from handler

import axios from 'axios';
axios.defaults.withCredentials = true;

export default async function handler(req, res){
   try {
     const response = axios.post('http://localhost:4000/<your_login_api_URL>', req.body)
   }catch(error) {
     // handle error here
   }

}

this will work and its safer way to mask your back end API calls from front end.