Domain (TXT)
Differentiate between domain and domain name server and components of DNS
Domain could be a piece of string that helps to spot a specific web sit
DNS (Domain Name System) could be a server that translates the domain to the corresponding ip address to supply the specified webpage
Add custom domain to azure
The unverified domain is added. The contoso.com page appears showing your DNS information. Save this information. You need it later to create a TXT record to configure DNS.
After you add your custom domain name to Azure AD, you must return to your domain registrar and add the Azure AD DNS information from your copied TXT file.
Go back to your domain registrar and create a new TXT record for your domain based on your copied DNS information. Set the time to live (TTL) to 3600 seconds (60 minutes), and then save the record.
https://learn.microsoft.com/en-us/azure/active-directory/fundamentals/add-custom-domain
Tutorial: Host your domain in Azure DNS | Microsoft Learn
DNS Zone (A)
A DNS zone contains the DNS entries for a domain. To start hosting your domain in Azure DNS, you create a DNS zone for that domain name.
You can configure Azure DNS to resolve host names in your public domain. For example, if you purchased the contoso.xyz domain name from a domain name registrar, you can configure Azure DNS to host the contoso.xyz domain and resolve www.contoso.xyz to the IP address of your web server or web app.
You create DNS entries or records for your domain inside the DNS zone. Create a new address record or ‘A’ record to resolve a host name to an IPv4 address.
Since this quickstart is just for quick testing purposes, there’s no need to configure the Azure DNS name servers at a domain name registrar.
With a real production domain, you’ll want anyone on the Internet to resolve the host name to connect to your web server or app. You’ll visit your domain name registrar to replace the name server records with the Azure DNS name servers. For more information, see Tutorial: Host your domain in Azure DNS.
https://learn.microsoft.com/en-us/azure/dns/dns-getstarted-portal
Private DNS (A ++)
Azure Private DNS provides a reliable and secure DNS service for your virtual network. Azure Private DNS manages and resolves domain names in the virtual network without the need to configure a custom DNS solution.
By using private DNS zones, you can use your own custom domain name instead of the Azure-provided names during deployment
You can also enable autoregistration on a virtual network link. When you enable autoregistration on a virtual network link, the DNS records for the virtual machines in that virtual network are registered in the private zone.
When autoregistration gets enabled, Azure DNS will update the zone record whenever a virtual machine gets created, changes its’ IP address, or gets deleted.
Use all common DNS records types. Azure DNS supports A, AAAA, CNAME, MX, PTR, SOA, SRV, and TXT records.
What is Azure Private DNS? | Microsoft Learn
Map an existing custom DNS name to Azure App Service (CNAME)
CNAME record. You can map a subdomain to the app’s IP address directly with an A record, but it’s possible for the IP address to change. The CNAME maps to the app’s default hostname instead, which is less susceptible to change.
For TLS/SSL certificate, select App Service Managed Certificate if your app is in Basic tier or higher. If you want to remain in Shared tier, or if you want to use your own certificate, select Add certificate later.