add tutorial on custom domain migration (#2647)

Author: thisisjofrank

deploy/images/dns_config.png

@@ -175,3 +175,10 @@ organization for use with other applications.
 
 This removes the custom domain from your organization and deletes all domain
 assignments across all applications.
+
+## Migrating a custom domain from Deploy Classic top Deno Deploy
+
+If you have previously set up a custom domain on Deploy Classic and want to
+migrate it to Deno Deploy, we've created a
+[step-by-step tutorial](/examples/migrate_custom_domain_tutorial/) to guide you
+through the process.

deploy/reference/domains.md

@@ -405,6 +405,11 @@ export const sidebar = [
         href: "/examples/deploy_command_tutorial/",
         type: "tutorial",
       },
+      {
+        title: "Migrating a custom domain to Deno Deploy",
+        href: "/examples/migrate_custom_domain_tutorial/",
+        type: "tutorial",
+      },
       {
         title: "AWS Lambda",
         href: "/examples/aws_lambda_tutorial/",

examples/_data.ts

@@ -0,0 +1,45 @@
+---
+title: "Migrating a custom domain from Deploy Classic to Deno Deploy"
+description: "Learn how to migrate your custom domain from Deploy Classic to Deno Deploy"
+url: /examples/migrate_custom_domain_tutorial/
+---
+
+If you have previously set up a custom domain on Deploy Classic and want to
+migrate it to Deno Deploy, follow these steps:
+
+## Add your domain to Deno Deploy
+
+1. Visit the [Deno Deploy dashboard](https://dash.deno.com) and navigate to the
+   project you want to associate with your custom domain.
+
+2. Click the **"Settings"** tab.
+
+3. Under "Production Domains", click **"+ Add Domain"**.
+
+4. Enter your custom domain (e.g., `test.mywebsite.com`), select whether you
+   want just the base url or base and wildcard, then click **"Save"**.
+
+This will kick off DNS record configuration, which may take a few minutes.
+
+You will be presented with DNS records that you need to add to your DNS
+provider.
+
+## Provision a TLS certificate
+
+In your DNS provider's settings, update your domain's DNS records to include the
+provided `_acme-challenge` CNAME record. This is necessary for Deno Deploy to
+verify your domain and provision a TLS certificate.
+
+![DNS Records modal](/deploy/images/dns_config.png)
+
+Once the DNS records are picked up, provision a new TLS certificate by clicking
+the **"Verify DNS and provision certificate"** button.
+
+## Update DNS records
+
+In your DNS provider's settings, remove any existing CNAME/A/AAAA records for
+your domain and replace them with the CNAME or ANAME records provided by Deno
+Deploy.
+
+This may take some time due to DNS propagation delays. Allow up to 48 hours for
+the changes to take effect before removing the domain from Deploy Classic.