is it possible to access Google Cloud SQL from Google Compute Engine using the private network?
It appears that Google Cloud SQL sees the public network IP for the Google Compute Engine instance.
And, the web console doesn't allow entering the instance private address.
No it is not possible to access Google Cloud SQL instances via a private IP address.
This this page confirms this, it says Note: You must use the external (public) IP address of the GCE instance ...when configuring Authorized IP Addresses to your cloud sql instance from your GCE instance.
This is now available via private services access and VPC Network Peering.
The announcement:
Details:
You can't access cloud sql from a private IP address but you can whitelist NAT instance's Public IP in order to access cloudsql from private server.
来源：https://stackoverflow.com/questions/22891702/accessing-google-cloud-sql-from-google-compute-engine-using-private-network