Amazon AWS - PHP with MySQL

I am working on an Android App with basic user signup/login. Currently I have got it working on my localhost with WAMP Server running.

I wanted to take it a step further by taking Amazon RDS (MySQL) instance and hosting my php files on some server (probably EC2 Instance) and allowing the Android App to make a HTTP Request to the php file, which inturn connects to the MySQL instance.

So far I have created a MySQL Instance and an EC2 instance (with LAMP setup). I am unable to connect to the MySQL instance from the EC2 instance ( I ssh into the EC2 via Putty, and tried to connect to MySQL instance using this command mysql -h myinstance.123456789012.us-east-1.rds.amazonaws.com -P 3306 -u mymasteruser -p).

I think it is due to the VPC security groups setup, which I am unable to configure for the MySQL Instance.

The EC2 & RDS instance are in Singapore region. Here is a snapshot of the VPC I have:

Any suggestions or links to some resources to sort this out would be highly appreciated.