A subset of the official cloud-config spec is implemented by coreos-cloudinit. Additionally, several CoreOS-specific options have been implemented to support interacting with unit files, bootstrapping etcd clusters, and more. All supported cloud-config parameters are documented here.

The following is an example cloud-config document:

#cloud-config

coreos:
    units:
      - name: etcd.service
        command: start

users:
  - name: core
    passwd: $1$allJZawX$00S5T756I5PGdQga5qhqv1

write_files:
  - path: /etc/resolv.conf
    content: |
        nameserver 192.0.2.2
        nameserver 192.0.2.3

Executing a Script

coreos-cloudinit supports executing user-data as a script instead of parsing it as a cloud-config document. Make sure the first line of your user-data is a shebang and coreos-cloudinit will attempt to execute it:

#!/bin/bash

echo 'Hello, world!'

user-data Field Substitution

coreos-cloudinit will replace the following set of tokens in your user-data with system-generated values.

Token	Description
$public_ipv4	Public IPv4 address of machine
$private_ipv4	Private IPv4 address of machine

These values are determined by CoreOS based on the given provider on which your machine is running. Read more about provider-specific functionality in the CoreOS OEM documentation.

For example, submitting the following user-data...

#cloud-config
coreos:
    etcd:
        addr: $public_ipv4:4001
        peer-addr: $private_ipv4:7001

...will result in this cloud-config document being executed:

#cloud-config
coreos:
    etcd:
        addr: 203.0.113.29:4001
        peer-addr: 192.0.2.13:7001