Ensuring DNS Prefix Reuse for Migration from Application Gateway to VM Proxy

Question

Ensuring DNS Prefix Reuse for Migration from Application Gateway to VM Proxy

Leszek Jaskierny 0

Due to the end of TLS 1.1 support on Azure Application Gateway, several of our IoT devices can no longer connect to their API endpoints. We need to deploy a simple VM acting as a proxy, but it must use the exact same DNS name as our current Application Gateway (xxx.westeurope.cloudapp.azure.com). Losing this DNS prefix would permanently disconnect remote devices that cannot be updated. Could you advise how to safely reuse this DNS label on the VM (e.g., coordinated release/reassignment), and whether Microsoft Support can assist to ensure a seamless migration without risk of losing the prefix?

Leszek Jaskierny 0 Reputation points

2025-11-22T06:29:18.11+00:00

how can I reach to Microsoft Support directly.
Leszek Jaskierny 0 Reputation points

2025-11-22T06:34:17.6666667+00:00

I know already the process provided in the answer. My only concern is how I can make sure I won't loose my subdomain during the migration.
Adam Zachary 2,025 Reputation points

2025-11-24T00:22:05.7233333+00:00

I’ve done this before, and the key thing to understand is that the cloudapp.azure.com DNS prefix is tied to the public IP resource, not the Application Gateway itself. That means you can reuse the exact same DNS name, but only if you keep the same public IP.

The safe way to do this is simple. Do not delete the Public IP that your Application Gateway is using. Instead, detach it from the Application Gateway, then attach that same Public IP to the VM or the NIC or load-balancer you’re using for the proxy. As long as the Public IP resource stays intact, the DNS label xxx.westeurope.cloudapp.azure.com remains yours.

You do not need coordinated release or Microsoft Support unless someone accidentally deletes the Public IP. If that happens, the DNS name becomes globally available again, and it’s not guaranteed you can get it back.

So the safe migration path is to keep the original Public IP, stop the Application Gateway, detach the IP, and then attach that IP to your VM. That guarantees the DNS name stays exactly the same and your IoT devices continue to work.
Thanmayi Godithi 2,215 Reputation points Microsoft External Staff Moderator

2025-11-27T05:01:09.95+00:00

Hi @Leszek Jaskierny,

Just checking in to see if you had a chance to see the previous response posted by me.

Please "Upvote" if the information helped you. This will help us and others in the community as well.

If you have any further questions do let us know.

Regards,

Thanmayi

1 answer

Your answer

Leszek Jaskierny 0 Reputation points

2025-11-22T06:29:18.11+00:00

how can I reach to Microsoft Support directly.
Leszek Jaskierny 0 Reputation points

2025-11-22T06:34:17.6666667+00:00

I know already the process provided in the answer. My only concern is how I can make sure I won't loose my subdomain during the migration.
Adam Zachary 2,025 Reputation points

2025-11-24T00:22:05.7233333+00:00

I’ve done this before, and the key thing to understand is that the cloudapp.azure.com DNS prefix is tied to the public IP resource, not the Application Gateway itself. That means you can reuse the exact same DNS name, but only if you keep the same public IP.

The safe way to do this is simple. Do not delete the Public IP that your Application Gateway is using. Instead, detach it from the Application Gateway, then attach that same Public IP to the VM or the NIC or load-balancer you’re using for the proxy. As long as the Public IP resource stays intact, the DNS label xxx.westeurope.cloudapp.azure.com remains yours.

You do not need coordinated release or Microsoft Support unless someone accidentally deletes the Public IP. If that happens, the DNS name becomes globally available again, and it’s not guaranteed you can get it back.

So the safe migration path is to keep the original Public IP, stop the Application Gateway, detach the IP, and then attach that IP to your VM. That guarantees the DNS name stays exactly the same and your IoT devices continue to work.
Thanmayi Godithi 2,215 Reputation points Microsoft External Staff Moderator

2025-11-27T05:01:09.95+00:00

Hi @Leszek Jaskierny,

Just checking in to see if you had a chance to see the previous response posted by me.

Please "Upvote" if the information helped you. This will help us and others in the community as well.

If you have any further questions do let us know.

Regards,

Thanmayi

Answer 1

Hi @Leszek Jaskierny,

Can you confirm whether the Public IP address assigned to the Application Gateway is configured as Static or Dynamic?”

The DNS name you want to reuse (e.g., xxx.westeurope.cloudapp.azure.com) is tied directly to the Public IP resource, not the Application Gateway itself.

If the Public IP is Static, we can safely detach it from the Gateway and reattach it to the VM, keeping the same DNS name without risk.
If the Public IP is Dynamic, the IP (and its DNS label) is released as soon as the Gateway is removed or reconfigured, which means the DNS prefix could be lost or taken by someone else.

Refer: https://learn.microsoft.com/en-us/azure/virtual-network/ip-services/virtual-network-public-ip-address#create-a-public-ip-address

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Kindly let us know if the above helps or you need further assistance on this issue.

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".

Thanks,

Thanmayi

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Ensuring DNS Prefix Reuse for Migration from Application Gateway to VM Proxy

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