How to create dynamic subdomains for each user using node express?

Question

On signup, I want to give user his profile and application at username.example.com I have already created wild-card dns at my domain provider website.

How can I do that?

Answer 1

If using Node.js with Express.js, then:

router.get('/', function (req, res) { 
    var domain = req.get('host').match(/\w+/); // e.g., host: "subdomain.website.com"
    if (domain)
       var subdomain = domain[0]; // Use "subdomain"
    ...
});

Answer 2

I got here because I wanted to do exactly what OP asked:

On signup, I want to give user his profile and application at username.example.com

The previous answers are ways to handle incoming requests from the already provisioned subdomains. However, the answers led me to thinking what I want is actually really straightforward - here goes:

// Creating the subdomain

app.post('/signup', (req, res) => {
  const { username } = req.body;

  //... do some validations / verifications
  // e.g. uniqueness check etc

  res.redirect(`https://${username}.${req.hostname}`);
})

// Handling requests from the subdomains: 2 steps
// Step 1: forward the request to other internal routes e.g. with patterns like `/subdomain/:subdomain_name/whatever-path`

app.use((req, res, next) {

  // if subdomains
  if (req.subdomains.length) {

    // this is trivial, you should filtering out things like `www`, `app` or anything that your app already uses.

    const subdomain = req.subdomains.join('.');

    // forward to internal url by reconstructing req.url

    req.url = `/subdomains/${subdomain}${req.url}`
  }
  return next()
});

// Handling requests from the subdomains: 2 steps
// Step 2: Have router setup for handling such routes
// you must have created the subdomainRoutes somewhere else

app.use('/subdomains/:subdomain', subdomainRoutes)

Hope it helps.