无法列出书籍:错误1046:未选择数据库

1) I'm working through the bookshelf tutorial using Golang and Cloud SQL (MySQL).

Link to Tutorial:

https://cloud.google.com/go/getting-started/using-cloud-sql

2) I'm been able to deploy to app engine successfully.

3) I'm able to add, edit, delete books successfully in the cloud.

THE PROBLEM:

After a certain amount of time has elapsed, I get the following error message in the browser:

"could not list books: Error 1046: No database selected"

The problem goes away when I redeploy using the following command:

$ aedeploy gcloud preview app deploy app.yaml

QUESTION:

Any idea why this could be happening: Initial success followed by Error 1046 after a certain amount of time has elapsed?