Cloudflare DNS can be used as an alternative DNS to Google Cloud DNS. Here are the steps how to enable Cloudflare DNS.
As a first step you will need to sign up to Cloudflare or you can use an existing account. Signing up for Cloudflare is easy and takes less than 5 minutes to configure.
Once you sign up you'll be guided through an easy setup wizard where you need to add domain name of your Google Cloud Project. Please note that Cloudflare DNS can only be enabled for root level domains, so you would add "example.com" not "subdomain.example.com."
For Cloudflare and Google Cloud Project to work together, you will need to update the DNS records on Cloudflare to point to your Google Cloud Instances.
First, find the external IP address for your instance:
Then enter that IP address for the A record of the subdomain that you want this instance to power:
Make sure that the subdomain is "orange clouded" and that you have updated the nameservers at your registrar to use Cloudflare's nameservers, and traffic will flow through Cloudflare to your Google Cloud instance!