azurerm_dns_cname_record

resource:
  azurerm_resource_group:
    test:
      name: acceptanceTestResourceGroup1
      location: 'West US'
  azurerm_dns_zone:
    test:
      name: mydomain.com
      resource_group_name: '${azurerm_resource_group.test.name}'
  azurerm_dns_cname_record:
    test:
      name: test
      zone_name: '${azurerm_dns_zone.test.name}'
      resource_group_name: '${azurerm_resource_group.test.name}'
      ttl: 300
      records:
        - contoso.com

resource "azurerm_resource_group" "test" {
   name = "acceptanceTestResourceGroup1"
   location = "West US"
}
resource "azurerm_dns_zone" "test" {
   name = "mydomain.com"
   resource_group_name = "${azurerm_resource_group.test.name}"
}

resource "azurerm_dns_cname_record" "test" {
   name = "test"
   zone_name = "${azurerm_dns_zone.test.name}"
   resource_group_name = "${azurerm_resource_group.test.name}"
   ttl = "300"
   records = ["contoso.com"]
}