AWS Lambda Cannot Access RDS via JDBC - amazon-web-services

Question

I have a test Lambda function setup using Java 8
So far I have
given the Lambda function an execution role AWSLambdaVPCAccessExecutionRole
attached the Lambda function to the only VPC I have on my account and selected all subnets within the VPC so that it may access the
my RDS instance in this case is open to the public, and I am able to access it via my Laptop (i.e. the Lambda code actually runs on remote hosts not inside the VPC)
security group assigned to the Lambda is the most permissive possible (i.e all traffic on all CIDR block)
However, I am still unable to access my RDS instance when running the Lambda function on AWS (but the same code works on my laptop, when run from a main() function)
Sample Code
public class Application implements RequestHandler<Object, Boolean> {
private Logger logger = Logger.getLogger(Application.class);
public Boolean handleRequest(Object object, Context context) {
try {
Class.forName("com.mysql.jdbc.Driver");
logger.info("Calling DriverManager.getConnection()");
Connection con = DriverManager.getConnection(
"jdbc:mysql://...endpoint...defaultdb",
"awsops",
"..."
);
Statement stmt = con.createStatement();
logger.info("Test Started!");
ResultSet result = stmt.executeQuery("SELECT\n" +
" last_name, COUNT(*)\n" +
"FROM\n" +
" users\n" +
"GROUP BY\n" +
" last_name\n" +
"HAVING COUNT(*) > 1");
if (result.next()) {
logger.info(result.getString("last_name"));
}
return true;
} catch (Exception e) {
logger.info(e.getLocalizedMessage());
}
return false;
}
}
Can you please help me understand what I could be doing wrong?
The CloudWatch logs shows that the function hangs at DriverManager.getConnection()

Answer 1

It turns out my RDS was launched with an automatically created security group that literally just whitelisted my personal IP address ... so it feels like I was able to connect to it from 'anywhere'
I had to update the security group of my RDS instance to allow traffic from the subnets where the Lambda's virtual network interface could be coming from