Azure private DNS behaviour with Azure Site recovery

Deepankar Pal 20

Hi All,

I have a private DNS zone setup in my primary region with auto registration enabled for linked Virtual Network. I have linked VNets from primary and Secondary region. In the event of a VM failover through Azure Site recovery, will the auto registered A record in the private DNS be updated automatically or do I need to manually update it ?

Thanks in advance

Deepankar

GitaraniSharma-MSFT 49,641 Reputation points Microsoft Employee

2023-09-28T10:33:27.3433333+00:00

Hello @Deepankar Pal ,

Welcome to Microsoft Q&A Platform. Thank you for reaching out & hope you are doing well.

Please allow me some time to check on this and get back to you. Will keep you posted.

Regards,

Gita
GitaraniSharma-MSFT 49,641 Reputation points Microsoft Employee

2023-10-04T15:18:14.65+00:00

Hello @Deepankar Pal ,

Apologies for the delay in response.

I discussed this scenario with Azure DNS Product Group team and below is their response:

If a VM instance has an auto registered record, and you delete the VM, the record will be deleted automatically (What is auto registration feature in Azure DNS private zones? | Microsoft Learn). For any other updates, you would have to do this manually.

For azure site recovery specifically, I believe Private DNS only supports private endpoint scenarios listed here (Enable replication for private endpoints in Azure Site Recovery - Azure Site Recovery | Microsoft Learn).

However, since I'm not from the site recovery team, I may need to understand how the VM failover actually happens.

Because as mentioned in the Azure Private DNS FAQ,

What causes the automatically registered virtual machine DNS records in a private zone be created or deleted? When you start a virtual machine within a linked virtual network with autoregistration enabled, DNS records are automatically created for that virtual machine. When you stop a virtual machine and it is deallocated, the autoregistered DNS records are removed.

So, if both Primary and Secondary region Vnets are linked to Private DNS zone with auto registration enabled, and the primary VM stops, the existing DNS record will be automatically deleted and when a new VM is created in the secondary region, a new DNS record should be auto created.

But if I read through the Azure VMs failover to a secondary region using Azure Site recovery document, it says:

Select Shut down machine before beginning failover if you want Site Recovery to try to shut down the source VMs before starting failover. Shutdown helps to ensure no data loss. Failover continues even if shutdown fails. After the failover, the Azure VM created in the target region appears in Virtual Machines.

So, the only thing which could lead to an issue is the failure of primary region VM's shutdown process. If the shutdown fails, then the existing record will not be auto deleted and a new record will not be created. In such a case, you will have to do a manual update.

Regards,

Gita

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Azure private DNS behaviour with Azure Site recovery

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