Hi Folks,
My 2 cents on this…
Here is the example of the Proxy DNS configuration :
set interface ethernet1/2.1 proxy dns
set dns host dns1 <snipped>
set dns host dns2 <snipped>
set dns proxy
set dns proxy enable
set dns server-select domain <snipped> outgoing-interface ethernet0/0 primary-server <x> secondary-server <snipped> tertiary-server <snipped> failover
https://kb.juniper.net/InfoCenter/index?page=content&id=KB4200