RDS Postgres, can connect from local but not from EC2

Okay this is a little weird, I have set up an RDS Postgres instance that I'm able to connect from pgAdmin and psql-commandline running locally, but not able to connect from command-line psql or webserver (flask) from the EC2 instance.

I'm guessing it has to do something with outbound connections from EC2 but my security group setting allows all outbound.

FYI: I have setup flask using elasticbeanstalk if that makes any difference.