Error connecting from GAppEngine servlet to GoogleCloud MySQL only at first try

Question

Description:

Greetings, I have a Google App Engine standard web service deployed from Eclipse Oxygen that consists of a servlet connecting to a MySQL database with the same project id in the Google Cloud using hibernate. It is a simple event managing website where you (as an invitee) enter your email and a given code (don't worry about security at least here, please) and you confirm or cancel your assistance to a given event.

Error:

The error is the following, at localhost, the tested project will perform correctly on every connection and transference of data. But as soon as I deploy it, when I test it from the user side, on the first try (wether you confirm, cancel or enter invalid data) it will fail to connect to the database. If you redo the operation, it will work.

Information to take into account:

• I did not use the JDBC GoogleDriver (as I couldn't find a way to make it work [ClassNotFoundException...]). I use "com.mysql.jdbc.Driver".
• The database allows the IP 0.0.0.0/0 (everyone) to connect to it (I know, security issues).
• The servlet access the database with root + password (more security issues...).
• When the user confirms/cancels the servlet will ask the Business class instance to retrieve the user data to check if it pairs it's invitation code.

Notice:

I have no idea how is this happening. Please, ask me for the details you need, and I will edit this question with them, because I don't know where to start. I'm pretty sure this first-try-only pattern must be easily identifiable to anyone who had experienced this . Thank you very much.

Answer 1

When thing is running correctly on localhost then obviously Google Cloud has specific issue. Google Cloud's 0.0.0.0/0 is not really "whole earth". You have to add subnet from which you'll connect. That much I know.

Better you can test on some PaaS like Bluemix. Bluemix has own big Q&A - developer.ibm.com/answers/ plus StackOverflow.

Of course you can use VPS as other option than PaaS. Essentially you need to run an application NOT fight with some platform.