# 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][cloud-config] 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. [cloud-config]: http://cloudinit.readthedocs.org/en/latest/topics/format.html#cloud-config-data ## 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][etcd-config]. Note that hyphens in the coreos.etcd.* keys are mapped to underscores. [etcd-config]: https://github.com/coreos/etcd/blob/master/Documentation/configuration.md ### 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 - **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. ### 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 `:` argument to `chown : `.