Hi @Himanshu Sekhar Mohanty
Thanks for the question and using MS Q&A platform.
In Azure portal, validate the custom domain after creating a DNS zone in Azure Private DNS, and add CNAME record for your custom domain. This CNAME record should be mapped to the Azure App Service hostname.
Regarding your specific issue with multi-period domain names, you are correct that Azure may misinterpret the structure of the domain name. One workaround for this is to use a subdomain that does not contain multiple periods. For example, instead of using my-pr3.eu.azure.dev.com, you could use my-pr3.azure.dev.com or my-pr3.eu.azuredev.com.
If you still want to use the original domain name with multiple periods, you can try using a TXT record to validate the domain instead of a CNAME record. To do this, you would need to add a TXT record to the DNS zone that contains a verification code provided by Azure. Once the TXT record is added, you can validate the custom domain in the Azure portal.
references:
https://learn.microsoft.com/en-us/azure/dns/dns-web-sites-custom-domain#create-the-cname-record
https://learn.microsoft.com/en-us/azure/dns/private-dns-getstarted-portal
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