When it comes to establish the DR for Oracle AI Database@Azure, the process is simple and expects to provision a DR Oracle AI Database@Azure Exadata cluster or Autonomous Database Serverless in a cross-zone or cross-region type of configuration.

We will not discuss about specifics of Database configuration for DR, instead we will talk about a hot subject when it comes to DR, the DNS part and most specific when our customers uses the default DNS.

Let’s do a recap of DR networking typologies:

Exadata Database Service cross-zones DR

Exadata Database Service cross-regions DR

Autonomous Database Serverless cross-zones DR

Autonomous Database Serverless cross-regions DR

Like we mentioned, in each of the case the default DNS will be used.

To use the default DNS configuration, custom DNS must not be checked. The single field that can be modified is the field containing the Hostname prefix, the other two: Host Domain Name and Host and domain URL are not editable and are automatically completed by the system:

Now, we have arrived at the most interesting part. The Host domain name above will define the OCI DNS private zone name. Using the default DNS, the private zone will be also replicated to Microsoft Azure VNET where the delegated subnet is configured.

In case of a DR type of configuration, we need to make sure the DNS zone name for Active and DR is unique. This will simplify the on-premises or Azure DNS servers in creating DNS conditional forwarding rules in a unique way, each one for the DNS private zone of Active and DR.

How actually the Host domain name is formed? At the end, that will provide the DNS private zone name.

The rule used to automatically configure the Host domain name and finally to provide the DNS private zone name is:

oci+first_11_chars_of_delegated_subnet_name.oci+first_11_chars_of_vnet_name.oraclevcn.com

With this information in our pocket, let’s have an example:

  • VNET name: odb-multicloud-production-vnet
  • Subnet name: odb-multicloud-production-subnet
  • Host domain name: ociodbmulticlo.ociodbmulticlo.oraclevcn.com
  • DNS private zone name: ociodbmulticlo.ociodbmulticlo.oraclevcn.com

Is there any possibility for Active and DR to end up with the same DNS private zone name even if the VNETs and delegated subnets have different name? Let’s find out.

Active site:

  • VNET name: odb-multicloud-production-vnet
  • Subnet name: odb-multicloud-production-subnet
  • Host domain name: ociodbmulticlo.ociodbmulticlo.oraclevcn.com
  • DNS private zone name: ociodbmulticlo.ociodbmulticlo.oraclevcn.com

DR site:

  • VNET name: odb-multicloud-production-DR-vnet
  • Subnet name: odb-multicloud-production-DR-subnet
  • Host domain name: ociodbmulticlo.ociodbmulticlo.oraclevcn.com
  • DNS private zone name: ociodbmulticlo.ociodbmulticlo.oraclevcn.com

As we can see, even if the VNET name and subnet name are different, we can end up with the same DNS private zone name for Active and DR sites. This is not something we want. We can make the DNS private zone name unique only if we have a difference in the first 11 characters between Active and DR on either the VNET name or subnet name.

I hope this information will help designing the default DNS for Active/DR Oracle AI Database@Azure.