"cap ec2onrails:setup" requres password

I am running cap ec2onrails:setup to deploy my rails app. But I don't know why it asks for a password. Through the process of setting up an instance in EC2 I never encountered setting up admin password. Here is what's happening:

$ cap ec2onrails:setup
  * executing `ec2onrails:setup'
  * executing `ec2onrails:server:update_hostname'
  * executing "sudo -p 'sudo password: ' /usr/local/ec2onrails/bin/update_hostname"
    servers: ["ec2-50-16-15-138.compute-1.amazonaws.co开发者_如何学Cm"]
Password: 
connection failed for: admin@ec2-50-16-15-138.compute-1.amazonaws.com (Net::SSH::AuthenticationFailed: admin)

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Add the keypair you used to boot this instance to ssh and then run the same setup again

ssh-add <filename>