Do I need to update domain IP after service plan upgrade

Question

Do I need to update domain IP after service plan upgrade

JG 20

Hi

I’ve just upgraded my App Service Plan from S3 to P3V2

When I now look at the custom domains section on my web apps the IP address has changed. However everything still works as it did previously

do I need to update my DNS records to point to the new IP or will the old IP continue to work

VenkateshDodda-MSFT 25,111 Reputation points Microsoft Employee Moderator

2023-02-22T09:47:45.09+00:00

@JG I have updated my answer with more information. Request you to take a look and let me know if you have any further questions.

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VenkateshDodda-MSFT 25,111 Reputation points Microsoft Employee Moderator

2023-02-22T09:47:45.09+00:00

@JG I have updated my answer with more information. Request you to take a look and let me know if you have any further questions.

Answer 1

TP 125.8K Volunteer Moderator

Hi,

Yes, if your Inbound IP address changes and you have an DNS A record for your custom domain you need to update the record with the new address. If you are using only CNAME then no change is needed.

The Inbound IP address shouldn't change when you switch to different SKU as you describe. Typically it would change if you update the TLS/SSL binding (e.g. switch from/to IP binding). Please see article below for more information:

https://learn.microsoft.com/en-us/azure/app-service/overview-inbound-outbound-ips#when-inbound-ip-changes

If the above is helpful please click Accept Answer.

Thanks.

-TP

JG 20 Reputation points

2023-02-22T07:40:58.1133333+00:00

Hummm I’m very confused as the IP address listed in the custom domains is definitely different since upgrading Service Plan.

I have www records as CNAME records but root DNS is A record pointing to domain.

I have access to some of the DNS for sites but others are managed by someone else. I’ve amended IP on one site to new IP and it seems that both IP are working….

Is it possible for both IP to be working?

and should I be updating all A Records to the new IP.
TP 125.8K Reputation points Volunteer Moderator

2023-02-22T08:01:20.82+00:00

@JG Yes, you should update all A records to the new IP. You should not rely on the old IP continuing to work just because it works now. It may be that the service has an underlying implementation detail of the "gateway/load balancer" component that keeps previous inbound forwarding/balancing rules in place for a certain amount of time after IP change to keep sites from breaking immediately. Or some other implementation detail that happens to mean previous IP address works.

Key thing is, don't depend on undocumented behavior if you can help it.

In my experience the Inbound IP doesn't change solely from SKU change, however, just because that has been my experience I'm not suggesting what you experienced is impossible. To confirm, I just did quick test where I created new app service plan with custom domain and switched back and forth between various Free/Basic/Standard/Premium SKUs and the Inbound IP didn't change. It did change if I updated the binding to IP from SNI.

-TP
JG 20 Reputation points

2023-02-22T11:18:25.9133333+00:00

Thank you TP. Very helpful. As I don't control DNS, I just wanted to ensure I wasn't making a change that I shouldn't be. I mean it makes total sense to change the IP to the new one, just confuses me slightly that it still works.

Answer 2

VenkateshDodda-MSFT 25,111 Microsoft Employee Moderator

@JG

Thank you for reaching out to Microsoft Q&A.

If your custom domain is having CName recording pointing to the root URL of the web app i.e., (https://<app.name>.azurewebsites.net) then there is no need to update your DNS records since CName record is resolving to the Hostname of the webapp instead to particular IP.

Update:

App service Inbound public Ip won't be changed when you scale up your app service plan from standard to Premium SKU. your App inbound IP Might be changed due IP SSL based certificate got bind to the custom domain of your web app.

As mentioned here in this documentation. By default, your app uses a shared public IP address. when you bind a certificate with IP SSL based app service will create a new dedicated Ip address for your app. If you mapped A record to your app then you need update your domain registry with the new dedicated Ip address.

Your app's Custom domain page is updated with the new, dedicated IP address. Copy this IP address, then remap the A record to this new IP address.
If you have an SNI SSL binding to <app-name>.azurewebsites.net, remap any CNAME mapping to point to sni.<app-name>.azurewebsites.net instead (add the sni prefix).

Feel free to reach back to me if you have any further question on this.

Thanks,

Venkatesh.

JG 20 Reputation points

2023-02-22T11:16:52.4+00:00

Thank you Venkatesh, I will update the IPs on the sites.

I just find it strange that whilst the IP has changed the sites continue to function. It this expected behaviour based on the underlying implementation? Can you explain this for my future reference.
VenkateshDodda-MSFT 25,111 Reputation points Microsoft Employee Moderator

2023-02-23T06:30:26.01+00:00

@JG Thanks for your response, I didnt understood your question Could you please elobrate it more
JG 20 Reputation points

2023-02-23T11:38:48.16+00:00

At the moment I have an old IP pointing to my site, yet it still works. I have updated to the new IP and works, so both are working. Is there a grace period before the old IP address will no longer work?
VenkateshDodda-MSFT 25,111 Reputation points Microsoft Employee Moderator

2023-02-28T05:46:16.2766667+00:00

@JG Thanks for your follow-up question, Apologize for the delay in my response. It is recommended to update/remap the dns records when you add the IP SSL based certificate for the webapp.

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Do I need to update domain IP after service plan upgrade

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