Alpha Coder
How to configure wildcard subdomains

Some web apps, especially those for the enterprise, give every organization, team or user their own subdomain such as team-name.awesomeapp.com or org-name.beta.awesomeapp.com. These subdomains are variable, meaning that they are not predefined and can contain any valid domain name characters.

To configure wildcard subdomains, all you need to do is add a “match all” CNAME record for your domain. The way a given subdomain is handled is totally up to your application. All web browsers and servers provide a medium for accessing a web app’s url for a given request, so you can fetch the subdomain and proceed with your business logic. Often, the subdomain would be a unique id for something e.g an organization, so your can use it to get the organization’s details for instance.

Here’s a sample application that displays avatars from Adorable Avatars based on the subdomain you use.

Visit some-random-name.wildcard-subdomains.alphacoder.xyz where some-random-name can be anything you like and watch the avatars change!

To use wildcard subdomains, go to your domain registrar and create a “match all” CNAME record

If you want subdomains like some-random-name.alphacoder.xyz, feel free to skip the .wildcard-subdomains so that you have only * in the host field.

The web page has just a few lines of code

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Wildcard subdomains</title>
</head>
<body>

  <h1 id="subdomain"></h1>
  <img id="avatar">

  <script>
    var subdomain = window.location.hostname.split('.')[0];
    document.getElementById('subdomain').textContent = subdomain;
    var avatarSrc = 'https://api.adorable.io/avatars/285/' + subdomain + '.png';
    document.getElementById('avatar').src = avatarSrc;
  </script>
</body>
</html>

The most important part of the code is line 12, which gets the subdomain from the hostname (window.location.hostname.split('.')[0]).

In development, you can use lvh.me (e.g some-random-name.lvh.me:8080) to test your application instead of 127.0.0.1. some-random-name.localhost also works on browsers I’ve tested.


Last modified on 2019-04-02

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