cloudinit/Documentation/cloud-config.md

Customize CoreOS with Cloud-Config

CoreOS allows you to configure machine parameters, launch systemd units on startup and more. Only a subset of cloud-config functionality is implemented. A set of custom parameters were added to the cloud-config format that are specific to CoreOS.

Supported cloud-config Parameters

ssh_authorized_keys

Provided public SSH keys will be authorized for the core user.

The keys will be named "coreos-cloudinit" by default. Override this with the --ssh-key-name flag when calling coreos-cloudinit.

users

Add or modify users with the users directive by providing a list of user objects, each consisting of the following fields. Each field is optional and of type string unless otherwise noted. All but the passwd and ssh-authorized-keys fields will be ignored if the user already exists.

• name: Required. Login name of user
• gecos: GECOS comment of user
• passwd: Hash of the password to use for this user
• homedir: User's home directory. Defaults to /home/
• no-create-home: Boolean. Skip home directory createion.
• primary-group: Default group for the user. Defaults to a new group created named after the user.
• groups: Add user to these additional groups
• no-user-group: Boolean. Skip default group creation.
• ssh-authorized-keys: List of public SSH keys to authorize for this user
• system: Create the user as a system user. No home directory will be created.
• no-log-init: Boolean. Skip initialization of lastlog and faillog databases.

The following fields are not yet implemented:

• inactive: Deactivate the user upon creation
• lock-passwd: Boolean. Disable password login for user
• sudo: Entry to add to /etc/sudoers for user. By default, no sudo access is authorized.
• selinux-user: Corresponding SELinux user
• ssh-import-id: Import SSH keys by ID from Launchpad.

Generating a password hash

Generating a safe hash is important to the security of your system. Currently with updated tools like oclhashcat simplified hashes like md5crypt are trivial to crack on modern GPU hardware. You can generate a "safer" hash (read: not safe, never publish your hashes publicly) via:

On Debian/Ubuntu (via the package "whois")

mkpasswd --method=SHA-512 --rounds=4096

With OpenSSL (note: this will only make md5crypt. While better than plantext it should not be considered fully secure)

openssl passwd -1

With Python (change password and salt values)

python -c "import crypt, getpass, pwd; print crypt.crypt('password', '\$6\$SALT\$')"

With Perl (change password and salt values)

perl -e 'print crypt("password","\$6\$SALT\$") . "\n"'

Using a higher number of rounds will help create more secure passwords, but given enough time, password hashes can be reversed. On most RPM based distributions there is a tool called mkpasswd available in the expect package, but this does not handle "rounds" nor advanced hashing algorithms.

Custom cloud-config Parameters

coreos.etcd.discovery_url

The value of coreos.etcd.discovery_url will be used to discover the instance's etcd peers using the etcd discovery protocol. Usage of the public discovery service is encouraged.

coreos.units

Arbitrary systemd units may be provided in the coreos.units attribute. coreos.units is a list of objects with the following fields:

• name: string representing unit's name
• runtime: boolean indicating whether or not to persist the unit across reboots. This is analagous to the --runtime flag to systemd enable.
• content: plaintext string representing entire unit file

See docker example below.

user-data Script

Simply set your user-data to a script where the first line is a shebang:

#!/bin/bash

echo 'Hello, world!'

Examples

Inject an SSH key, bootstrap etcd, and start fleet

#cloud-config

coreos:
	etcd:
		discovery_url: https://discovery.etcd.io/827c73219eeb2fa5530027c37bf18877
    fleet:
        autostart: yes
ssh_authorized_keys:
  - ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC0g+ZTxC7weoIJLUafOgrm+h...

Start a docker container on boot

#cloud-config

coreos:
    units:
      - name: docker-redis.service
        content: |
          [Unit]
          Description=Redis container
          Author=Me
          After=docker.service

          [Service]
          Restart=always
          ExecStart=/usr/bin/docker start -a redis_server
          ExecStop=/usr/bin/docker stop -t 2 redis_server
          
          [Install]
          WantedBy=local.target

Add a user

#cloud-config

users:
  - name: elroy
	passwd: $6$5s2u6/jR$un0AvWnqilcgaNB3Mkxd5yYv6mTlWfOoCYHZmfi3LDKVltj.E8XNKEcwWm...
	groups:
	  - staff
	  - docker
	ssh-authorized-keys:
	  - ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC0g+ZTxC7weoIJLUafOgrm+h...