How to create subdomains in Route 53 and make www and the bare domain lead to the same site

A domain is good for much more than one website. You can have app.midominio.com on one machine, intranet.midominio.com on another and clientes.midominio.com on an external service, without buying anything else: they are subdomains, and in Route 53 each one is a single line. And then there is the eternal question of www: making both ways of writing your domain lead to the same website. This guide solves both and clears up a common misunderstanding: DNS says where each name goes, but it does not redirect; the server does that.

Step by step

1. Open your domain's zone

   Route 53 console, Hosted zones, click your domain. You will see the records it already has: the root A record, perhaps the www one, the MX records for email. Each new subdomain will be one more record in this list.

2. Create a subdomain pointing to a machine of yours

   Create record. Name: just the front part (app; Route 53 adds the domain). Type A. Value: the machine's static IP. TTL 300. Create. Within a few minutes app.midominio.com reaches that machine; the machine's web server has to know how to answer for that name (a "virtual host" or "server block"), otherwise it will show the default website.

3. Create a subdomain pointing to an external service

   Your helpdesk, shop or newsletter provider tells you something like "create a CNAME from clientes to midominio.proveedor.com". So do exactly that: Create record, name clientes, type CNAME, value the name they gave you (without http:// and without a trailing slash). If the provider is an AWS service (CloudFront, a load balancer), use type A with the Alias toggle on and pick it from the dropdown.

4. Decide what to do with www

   First, both names must reach your server: the root with an A record to the IP, and www with another A record to the same IP (or a CNAME to midominio.com). That is as far as DNS goes. Second, choose which one is the "official" name (nowadays usually without www) and have the other one redirect to it, so that Google does not see two identical websites and the padlock works on both.

5. Do the redirect on the server

   This is not done in Route 53. On the machine, the web server has to answer www.midominio.com with a permanent redirect (code 301) to midominio.com. In Apache, in the site's block:

   RewriteEngine On
   RewriteCond %{HTTP_HOST} ^www\.midominio\.com$ [NC]
   RewriteRule ^(.*)$ https://midominio.com/$1 [R=301,L]

   In Nginx it is a server block for www with a return 301. If you use the Bitnami blueprints on Lightsail, the bncert-tool asks exactly this when setting up the certificate and configures it for you. The HTTPS certificate must cover both names.

6. Check and raise the TTL

   Open all four combinations (with and without www, with http and https): all of them must end up at https://midominio.com with the padlock. Open the new subdomain. Once everything has been stable for a few days, raise the TTL of the records to 3600 or more: fewer queries and faster answers.

What can go wrong