I have hosted my website in Microsoft Azure. I have purchased the domain from register.com.
I have used a Linux VM for my project deployment.
Suppose my website name is example.com. I have created a sub domain for it called app.example.com
It was working fine but its not working when i created a DNS Zone resource in my azure account & updated those nameserver name in my register.com site.
According to your description, we can follow those steps to setup Azure DNS zone and your domain name:
1. Add record set via azure portal, point to your Azure VM:
2.Add NS record to register.com, like this:
Host: web.jasonye.com
Record type: NS record
Value: ns1-01.azure-dns.com
After a few mins, we can use nslookup to verify name resoution is working or not:
nslookup -type=SOA jasonye.com
The following is an example response from the preceding command:
C:\Users>nslookup -type=SOA jasonye.com
Server: UnKnown
Address: 2404:f801:10:12e:fe::2
Non-authoritative answer:
jasonye.com
primary name server = ns1-01.azure-dns.com
responsible mail addr = azuredns-hostmaster.microsoft.com
serial = 1
refresh = 3600 (1 hour)
retry = 300 (5 mins)
expire = 2419200 (28 days)
default TTL = 300 (5 mins)
ns1-01.azure-dns.com internet address = 40.90.4.1
After that, we can access this web via IE:
More information about Azure DNS zone, please check this link.
Each registrar has their own DNS management tools to change the name server records for a domain. In the registrar's DNS management page, edit the NS records and replace the NS records with the ones Azure DNS created.
来源：https://stackoverflow.com/questions/43603048/subdomain-not-working-after-changing-the-nameservers