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cloudinit/Documentation/cloud-config.md
Brian Waldon a594e053f5 chore(doc): clean up formatting
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Customize with Cloud-Config

CoreOS allows you to configure networking, create users, launch systemd units on startup and more. We've designed our implementation to allow the same cloud-config file to work across all of our supported platforms.

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. An example file containing all available options can be found at the bottom of this page.

CoreOS Parameters

coreos.etcd

The coreos.etcd.* options are translated to a partial systemd unit acting as an etcd configuration file. We can use the templating feature of coreos-cloudinit to automate etcd configuration with the $private_ipv4 and $public_ipv4 fields. For example, the following cloud-config document...

#cloud-config

coreos:
    etcd:
        name: node001
        discovery: https://discovery.etcd.io/3445fa65423d8b04df07f59fb40218f8
        addr: $public_ipv4:4001
        peer-addr: $private_ipv4:7001

...will generate a systemd unit drop-in like this:

[Service]
Environment="ETCD_NAME=node001"
Environment="ETCD_DISCOVERY=https://discovery.etcd.io/3445fa65423d8b04df07f59fb40218f8"
Environment="ETCD_ADDR=203.0.113.29:4001"
Environment="ETCD_PEER_ADDR=192.0.2.13:7001"

For more information about the available configuration options, see the etcd documentation. Note that hyphens in the coreos.etcd.* keys are mapped to underscores.

coreos.oem

These fields are borrowed from the os-release spec and repurposed as a way for coreos-cloudinit to know about the OEM partition on this machine:

  • id: Lowercase string identifying the OEM
  • name: Human-friendly string representing the OEM
  • version-id: Lowercase string identifying the version of the OEM
  • home-url: Link to the homepage of the provider or OEM
  • bug-report-url: Link to a place to file bug reports about this OEM

coreos-cloudinit renders these fields to /etc/oem-release. If no id field is provided, coreos-cloudinit will ignore this section.

For example, the following cloud-config document...

#cloud-config
coreos:
  oem:
    id: rackspace
    name: Rackspace Cloud Servers
    version-id: 168.0.0
    home-url: https://www.rackspace.com/cloud/servers/
    bug-report-url: https://github.com/coreos/coreos-overlay

...would be rendered to the following /etc/oem-release:

ID="rackspace"
NAME="Rackspace Cloud Servers"
VERSION_ID="168.0.0"
HOME_URL="https://www.rackspace.com/cloud/servers/"
BUG_REPORT_URL="https://github.com/coreos/coreos-overlay"

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. Required.
  • runtime: Boolean indicating whether or not to persist the unit across reboots. This is analagous to the --runtime argument to systemd enable. Default value is false.
  • content: Plaintext string representing entire unit file. If no value is provided, the unit is assumed to exist already.
  • command: Command to execute on unit: start, stop, reload, restart, try-restart, reload-or-restart, reload-or-try-restart. Default value is restart.

NOTE: The command field is ignored for all network, netdev, and link units. The systemd-networkd.service unit will be restarted in their place.

Examples

Write a unit to disk, automatically starting it.

#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

Start the builtin etcd and fleet services:

# cloud-config

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

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.

#cloud-config

ssh_authorized_keys:
  - ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC0g+ZTxC7weoIJLUafOgrm+h...

hostname

The provided value will be used to set the system's hostname. This is the local part of a fully-qualified domain name (i.e. foo in foo.example.com).

#cloud-config

hostname: coreos1

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 creation.
  • 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
  • coreos-ssh-import-github: Authorize SSH keys from Github user
  • coreos-ssh-import-url: Authorize SSH keys imported from a url endpoint.
  • 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.
#cloud-config

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

Generating a password hash

If you choose to use a password instead of an SSH key, generating a safe hash is extremely important to the security of your system. Simplified hashes like md5crypt are trivial to crack on modern GPU hardware. Here are a few ways to generate secure hashes:

# On Debian/Ubuntu (via the package "whois")
mkpasswd --method=SHA-512 --rounds=4096

# OpenSSL (note: this will only make md5crypt.  While better than plantext it should not be considered fully secure)
openssl passwd -1

# Python (change password and salt values)
python -c "import crypt, getpass, pwd; print crypt.crypt('password', '\$6\$SALT\$')"

# 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.

Retrieving ssh authorized keys from a GitHub user

Using the field coreos-ssh-import-github you can make coreos-cloudinit to add the public ssh keys from a GitHub user as authorized keys to a server.

#cloud-config

users:
  - name: elroy
    coreos-ssh-import-github: elroy

Retrieving ssh authorized keys from an http endpoint

coreos-cloudinit can also pull public SSH keys from any http endpoint that matches GitHub's API response format. For example, if you have an installation of GitHub Enterprise, you can provide a complete url with an authentication token:

#cloud-config

users:
  - name: elroy
    coreos-ssh-import-url: https://token:<OAUTH-TOKEN>@github-enterprise.example.com/users/elroy/keys

You can also provide any url which response matches that json format for public keys:

#cloud-config

users:
  - name: elroy
    coreos-ssh-import-url: https://example.com/public-keys

write_files

Inject an arbitrary set of files to the local filesystem. Provide a list of objects with the following attributes:

  • path: Absolute location on disk where contents should be written
  • content: Data to write at the provided path
  • permissions: String representing file permissions in octal notation (i.e. '0644')
  • owner: User and group that should own the file written to disk. This is equivalent to the <user>:<group> argument to chown <user>:<group> <path>.