On Beanstalk configuration, edit the Instance by select key pair that you've create from EC2 console. Click save and wait until EB recreate the new instance.
Then navigate to EC2 console and find instance ID. If you don't know which instance then follow this http://docs.aws.amazon.com/elasticbeanstalk/latest/dg/using-features.ec2connect.html
Copy the Public DNS of the Instance and on your terminal;
$ ssh -i [yourkey.pem] ec2-user@[your-public-dns]
Once successfully login to your instance. You're logs are locate at /var/app/support/logs/ (production.log, passenger.log)
If you need to see the deployment logs. It's locate at /var/log/eb-tools.log, /var/log/cfn-init.log