cloud-config.yaml example for install coreos to disk....$ coreos-install -d /dev/sda -C stable -c cloud-config.yaml

cloud-config.example.yaml

#cloud-config

hostname: yourcorename

coreos:
  etcd:
    addr: $public_ipv4:4001
    peer-addr: $private_ipv4:7001
  units:
    - name: etcd.service
      command: start
    - name: fleet.service
      command: start
    - name: dhcp.network
      content: |
        [Match]
        Name=enp3s0

        [Network]
        DHCP=yes
users:
  - name: core
    passwd: # password hash, https://coreos.com/os/docs/latest/cloud-config.html
    groups:
      - sudo
      - docker
    ssh-authorized-keys:
      - ssh-rsa # your id_rsa.pub content