Impossible to `az network vnet update --dns-servers` if you haven't first set a Custom DNS server from the portal.

Hello all, I have recently tried to az network vent update --dns-servers a vnet that was using the default Azure DNS Servers. Upon doing so, the following stacktrace appears:

Dir: /home/tj/git/Movere.Dev.Builder [master] 
Usr: tj - Tue 24,  1:10PM > az network vnet update --name mov-dev-we-vnet --resource-group movere-dev-we --dns-servers 172.17.32.4 8.8.8.8
'NoneType' object has no attribute 'dns_servers'
Traceback (most recent call last):
  File "/usr/bin/azure-cli/lib/python3.6/site-packages/azure/cli/main.py", line 36, in main
    cmd_result = APPLICATION.execute(args)
  File "/usr/bin/azure-cli/lib/python3.6/site-packages/azure/cli/core/application.py", line 212, in execute
    result = expanded_arg.func(params)
  File "/usr/bin/azure-cli/lib/python3.6/site-packages/azure/cli/core/commands/__init__.py", line 377, in __call__
    return self.handler(*args, **kwargs)
  File "/usr/bin/azure-cli/lib/python3.6/site-packages/azure/cli/core/commands/arm.py", line 450, in handler
    raise ex
  File "/usr/bin/azure-cli/lib/python3.6/site-packages/azure/cli/core/commands/arm.py", line 405, in handler
    instance = custom_function(instance, **custom_func_args)
  File "/usr/bin/azure-cli/lib/python3.6/site-packages/azure/cli/command_modules/network/custom.py", line 1672, in update_vnet
    instance.dhcp_options.dns_servers = dns_servers
AttributeError: 'NoneType' object has no attribute 'dns_servers'

However, executing that command once you have set any arbitrary custom DNS server from the portal will succeed. This seems like a bug, but may not be based on the verb az network UPDATE. But I’m not sure.

If this is not the supported method to specify a DNS server for a vnet from the command line for the first time, please advise on how this should correctly be done.

[tjprescott]

Ah, @zimmertr thanks for that! I suspect after you run your deployments, if you show your VNET, you’ll see dhcpOptions: null. When the VNET is created using VNET create, you’d see:

dhcpOptions: {
   dnsServers: []
}

Which is why I couldn’t reproduce. I’ll get this fix into the next release (mid-November)

[jjindrich]

In powershell is not working az network vnet update -g myrg -n myvnet --dns-servers ‘’