ERROR initializing ubuntu user: subprocess encountered error code 255 (Permission denied (publickey).)

default: manual
environments:
  manual:
     type: manual
     bootstrap-host: deploy.example.com
     bootstrap-user: training

ssh deploy.example.com -l ubuntu

manual:
    type: manual
    # bootstrap-host holds the host name of the machine where the
    # bootstrap machine agent will be started.
    bootstrap-host: somehost.example.com

    # bootstrap-user specifies the user to authenticate as when
    # connecting to the bootstrap machine. It defaults to
    # the current user.
    # bootstrap-user: joebloggs

ssh deploy.example.com -l training

bootstrap-user: ubuntu