How to redirect multiple subdomains to the same running express app - node.js

Question

I'm building a SaaS app in NodeJS and using the Express framework. The individual members of the website has a url with a custom subdomain to login.
For example, a company called ABC Corp may login at abc.example.com and another company called Sony may login at sony.example.com
Any idea how I can redirect/route multiple subdomains to the same app instance?

Answer 1

You can use the express-subdomain package. Assuming you have a routes folder, containing abc.js and sony.js files that respectively export login routes for the abc and sony subdomains, you could have the following in index.js or whatever file from which your express server is listening.
const subdomain = require('express-subdomain');
const express = require('express');
const app = express();
const abcRoutes = require('./routes/abc');
const sonyRoutes = require('./routes/sony');
const port = process.env.PORT || 3000;
// use the subdomain middleware
app.use(subdomain('abc', abcRoutes));
app.use(subdomain('sony', sonyRoutes));
// a simple get route on the top-level domain
app.get('/', (req, res) => {
res.send('Welcome to the Home Page!');
});
// add any other needed routes
module.exports = app.listen(port, () => {
console.log('Server listening on port ' + port);
});
Your server will then be live and working as expected
http://example.com/ --> Welcome to the Home Page!
http://abc.example.com/login --> (Your login page for abc)
http://sony.example.com/login --> (Your login page for sony)
To tests subdomains locally you need to add them to your /etc/hosts file. (it requires sudo permissions)
127.0.0.1 localhost
127.0.0.1 example.com
127.0.0.1 abc.example.com
127.0.0.1 sony.example.com
The equivalent for /etc/hosts file on windows is at %systemroot%\system32\drivers\etc
For better details on setting up localhost domains locally check here
You can do more with the subdomain package. It accepts wildcards and you can use it to check API keys if you need such a feature.
Checkout the documentation for the express-subdomain package at https://npmjs.com/package/express-subdomain

Answer 2

You can actually handle that particular route or a wide range then go for Reg Exp (which allows you to do this app.get(new RegExp('(your|string)\/here'), function…) which you want to redirect and then follow the redirecting action something like below code is doing:
response.writeHead(302, {
'Location': 'yourpath/page.html'
//add other headers here...
});
response.end();
Update 1 : [as per the comments and other updates]
Then you try to handle all requests with the following app:
express()
.use(express.vhost('abc.example.com', require('/path/to/loginApp').app))
.use(express.vhost('sony.example.com', require('/path/to/loginApp').app))
.listen(80)
where /path/to/loginApp can be absolute paths or relative paths.
I hope this solves your problem.
Update 2:
Actually when a request comes in the request event is raised on a HTTP Server. So basically it is handled by express, express.vhost is a middle-ware function which raises the request event on another instance of a HTTP Server, that is how it works.
Below is the code:
function vhost(req, res, next){
if (!req.headers.host) return next();
var host = req.headers.host.split(':')[0];
if (req.subdomains = regexp.exec(host)) {
req.subdomains = req.subdomains[0].split('.').slice(0, -1);
server.emit('request', req, res);
} else {
next();
}
};