Is it possible to do a DNS Zone Transfer to Google Cloud DNS on Google Cloud Platform?
I can see references to Zone Transfers in the documentation (eg. https://cloud.google.com/dns/zones/) and elsewhere on the web, but cannot find any further information on it.
If it is possible, how do you do it?
TL;DR: You will need to EXPORT your current zone using a third party service or the tools provider by your service provider in BIND or YAML format and then IMPORT the zone to Google Cloud DNS.
On (https://cloud.google.com/dns/docs/migrating) you can find the detailed instructions on how to perform this procedure.
The export process heavily depends on your service provider. For example, if you are using GoDady you need to follow the instructions on (https://www.godaddy.com/help/export-my-domains-zone-file-records-4166).
It seems that AFXR/IFXR zone transfers are not supported on the Google Cloud Platform, at least currently at the time of posting.
https://stackoverflow.com/a/47123907/140872
The best way is to import in BIND format, as explained in Armando Cuevas's answer.