How do I add an A record to https://venio.acme.com into Azure DNS?

You would create an A record in Azure DNS by following these steps:

1. Open the Azure portal: Sign in to the Azure portal.

2. Navigate to the DNS zone: In the left menu, click on "All resources", find and select your DNS zone for 'acme.com'.

3. Open the DNS zone: Once in the DNS zone, click on the "Record set" button at the top of the page.

4. Configure the new record set:

   • In the "Name" field, enter 'venio'. This is because you're adding a record for 'venio.acme.com'. If you were adding a record for 'acme.com', you would leave this field blank.
   • In the "Type" dropdown, select "A". This is for an A record, which associates a domain or subdomain with an IPv4 address.
   • In the "TTL" field, enter the time-to-live value. This is how long, in seconds, the record can be cached by DNS resolvers. A common value is 3600, which equals one hour.
   • In the "TTL unit" dropdown, select the unit for the TTL. If you followed the suggestion above, you would select "Seconds".
   • In the "IP address" field, enter the public IPv4 address of the server you want to direct traffic to.

5. Save the record set: Click the "OK" button to create the record set.

Yes, if you want your domain or subdomain to be accessible over the internet, the IP address in the A record must be a public IP address.

Private IP addresses (such as those in the 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16 ranges) are not routable over the internet. They are typically used for internal network communication within a private network such as a home, office, or enterprise environment.

If you use a private IP address in an A record and attempt to access the domain or subdomain over the internet, the DNS lookup will return the private IP address, but the connection will fail because the IP address is not accessible over the internet.

So if your IIS server is hosted on a network with a private IP address and you want it to be accessible over the internet, you would typically use a router or firewall with Network Address Translation (NAT), or a similar method, to map a public IP address to the server's private IP address. In the A record, you would use the public IP address.

If your router or firewall is already forwarding port 443 to a different server with the same public IP, you have a few options.

1. Use a different port: You can configure the new server to use a different port (e.g., 8443), and then set up the router or firewall to forward traffic on that port to the new server. Note that users will need to specify the port in the URL when accessing the server (e.g., https://venio.acme.com:8443).

2. Use a reverse proxy: You can set up a reverse proxy on the web server that is currently receiving the port 443 traffic. The reverse proxy can inspect incoming requests and forward them to the appropriate server based on the hostname (e.g., acme.com goes to one server, venio.acme.com goes to another). Nginx and Apache with mod_proxy can both be used as reverse proxies.

3. Use a second public IP address: If your internet service provider (ISP) can provide you with a second public IP address, you can configure the router or firewall to forward port 443 traffic from the second public IP address to the new server.

Remember, regardless of the method you choose, you'll need to ensure that your DNS records are correctly configured to point to the right place (the public IP address of the router or firewall, or the second public IP address), and that the server is configured to accept traffic for the correct hostname.

It's important to note that DNS changes can take some time to propagate. This means that after you add the A record, it might take up to 48 hours (though often much less) for the change to be reflected across the entire internet.

Also, ensure that your server is configured to accept traffic for 'venio.acme.com', and that any firewalls are correctly configured to allow incoming traffic on the ports you're using (typically 80 for HTTP and 443 for HTTPS).