Bringing your own private DNS

Review this documentation if you are planning to use a private endpoint for Azure Postgres with your own private DNS.

Requirements and limitations

The following limitations apply when using your own private DNS:

Only Azure’s private DNS zone is supported. Using an on-prem DNS is not supported.
Private endpoints can only be used with a single customer-provided resource group. They cannot be used with CDP-created multiple resource groups. When creating an environment from the UI, the “Create Private Endpoints” option is disabled if you select the option for CDP to create multiple resource groups. If using CDP CLI, a validation error appears if this option is used with CDP creating multiple resource groups.
You can only use private endpoints with your own private DNS zone if you specify an existing VNet for the environment. If you chose CDP to create your network and enable private endpoints, then CDP is going to manage the private DNS zone for you.
The private DNS zone provided to CDP must have the name “privatelink.postgres.database.azure.com“. Furthermore, it must be in a subscription that is accessible to the service principal used by the CDP app-based credential; That is, the subscription where the private DNS zone is created must be in the same tenant where the service principal is located.

Prerequisites

When bringing your own private DNS, you should meet the following prerequisites:

Disable private endpoint network policies

Only subnets that have private endpoint network policies turned off are eligible for private endpoint creation, because network security groups (NSG) are not supported for private endpoints.

You can use the following Azure CLI command to disable private endpoint network policies for a certain subnet:

az network vnet subnet update \
  --name <subnet-name> \
  --resource-group <resource-group-name> \
  --vnet-name <vnet-name> \
  --disable-private-endpoint-network-policies true

For example:

az network vnet subnet update \
  --name default-2 \
  --resource-group my-cdp-rg \
  --vnet-name my-azure-vnet \
  --disable-private-endpoint-network-policies true

Create a private DNS zone and link it to your VNet

If you choose to provide your own Azure private DNS zone then you should:

Create a private DNS zone with the name “privatelink.postgres.database.azure.com“ in any subscription accessible to the service principal used by the CDP app-based credential; That is, the subscription where the private DNS zone is created must be in the same tenant where the service principal is located.
To create a private DNS zone, you can use the following Azure CLI command:
```
az network private-dns zone create \    
    --name privatelink.postgres.database.azure.com \
    --resource-group <YOUR_DNS_RESOURCE_GROUP> \
    --subscription <YOUR_SUBSCRIPTION_FOR_DNS>
```

Link it to the VNet that you are planning to use for the CDP environment.

You can do this using the following Azure CLI command:

az network private-dns link vnet create \
    --name <DESIRED_LINK_NAME> \
    --resource-group <YOUR_VNET_RESOURCE_GROUP> \
    --zone-name privatelink.postgres.database.azure.com \
    --virtual-network <YOUR_VNET_RESOURCE_ID> \
    --subscription <YOUR_VNET_SUBSCRIPTION>

Ensure that CDP has adequate permissions

Ensure that the role that you are using for the Azure credential has the permissions mentioned in Role definition 2: Allows CDP to access and use only a single existing resource group and create private endpoints.

Additionally, if your DNS zone is outside of the single resource group that you are planning to provide to CDP, the following additional permissions are required for the service principal to be able to discover, validate, and use the DNS zone (add and remove A records). These additional permissions need to be included in a separate role definition and assigned separately.

The placeholders in bold must be replaced with actual values:

{SUBSCRIPTION-ID} - The ID of the subscription where the DNS zone is located.
{RESOURCE-GROUP-NAME} - The name of the resource group where the DNS zone is located.

{
    "Name": "Cloudera Management Console Azure Operator for Using Private DNS Zones",
    "IsCustom": true,
    "Description": "Can list, validate and use private DNS zones",
    "Actions": [
      "Microsoft.Network/privateEndpoints/privateDnsZoneGroups/read",
      "Microsoft.Network/privateEndpoints/privateDnsZoneGroups/write",
      "Microsoft.Network/privateDnsZones/join/action",
      "Microsoft.Network/privateDnsZones/read",
      "Microsoft.Network/privateDnsZones/virtualNetworkLinks/read"
    ],
    "NotActions": [],
    "DataActions": [
    ],
    "NotDataActions": [],
    "AssignableScopes": [
      "/subscriptions/{SUBSCRIPTION-ID}/resourcegroups/{RESOURCE-GROUP-NAME}"
    ]
  }