在Google App Engine（弹性环境）中部署GO代码时出现Mysql连接问题

I am facing Mysql Connection issue , while migrating my code from Standard Environment to the Flexible Environment ( Google App Engine) .

I have even tried following : https://cloud.google.com/appengine/docs/flexible/go/using-cloud-sql

Stackoverflow link : Connecting to CloudSQL from App Engine (Second Generation CloudSQL) GO

But still not able to solve the issue . My case is :

I have even tried deploying the code given in above stackoverflow link (with my Cloud Sql) to test if it works . But in every case I am getting an error saying :

dial unix /cloudsql/butter-142812:us-central1:test: connect: no such file or directory

Where for me dbInstanceName  = butter-142812:us-central1:test

But everytime I am hitting the same problem . Can you please point out if I am missing something ?

I trying to deploy my app on Flexible Environment .