Cloud Sql

[Elavarasan Thiru]

What is Fail over in Cloud SQL? and What happens to the SQL server during fail-over? and After fail-over of master how the master recovers from failover

[Carlos (Cloud Platform Support)]

I believe most of your questions are answered on [1] and [2]. The event is triggered by an outage in the zone and existing connections are closed. Nevertheless your application can reconnect in the new zone using the same IP. 

This discussion provides additional insight (check Jay Zhu's comments) on how the failover is experienced in your side, which is basically seeing the master being moved to a healthy zone.