Application Proxy - page can't be found

Iron Contributor

I created an Application Proxy and it works as expected. I go to and it takes me to my app on the internal webserver.


However, I want to use a custom domain to get to the app. I changed the external url to and uploaded the certificate.


The next step says to change the CNAME record to have point to . However, as soon as I change the external url no longer works. I get the message:


"This page can’t be found

No webpage was found for the web address:"


Is this expected behaviour? I don't dare change the CNAME to point to somewhere I can't get to anymore.


Am I missing something?

4 Replies

@John Twohig Did you figure it out? I'm having this exact problem

@John Twohig 


How's your DNS handling?



I just went ahead and changed the CNAME record and it worked. I guess that is the expected behaviour. 


Maybe what I should have done is added a test CNAME record first and, after that worked, change the production CNAME record.

Hi @John
Yes, this behavior is expected. When you change the external URL of your application in Azure AD Application Proxy to use a custom domain, the original * URL will no longer be available. Azure AD Application Proxy updates its configuration to use the custom domain you specified, and the previous URL becomes inactive.

Here's what you should do:

1- Verify that you have changed the external URL in the Azure portal to use your custom domain (
2- Make sure you have uploaded the SSL certificate for your custom domain to the Azure AD Application Proxy settings.
3- Update the CNAME record in your DNS provider to point your custom domain ( to the original Azure AD Application Proxy domain ( This step is necessary to route traffic from your custom domain to the Application Proxy service.
4- Allow some time for the DNS changes to propagate. This can take up to 48 hours, but it usually happens much faster.
5- Test your custom domain ( to ensure that it routes correctly to your internal application.

It's important to note that once you've made these changes, you should use the custom domain ( to access your application instead of the original URL.

In summary, the behavior you're experiencing is expected, and you should proceed with updating your CNAME record as instructed. Once the DNS change propagates, you'll be able to access your application using the custom domain.