Cloud-init
External
- https://cloudinit.readthedocs.io/en/latest/
- http://cloudinit.readthedocs.org/en/latest/topics/examples.html
- https://wiki.archlinux.org/index.php/Cloud-init
- http://stackoverflow.com/questions/23411408/how-do-i-set-up-cloud-init-on-custom-amis-in-aws-centos
Internal
Overview
Cloud-init is an industry standard method for cross-platform cloud instance initialization. It is supported across all major cloud providers.
Cloud instances are initialized from a disk image and instance data. Instance data consists of:
- Cloud metadata
- User data
- Vendor data
Cloud-init identifies during boot the cloud the instance is running, reads any provided cloud metadata from the cloud and initializes the system accordingly - sets up network, storage, SSH access, etc. Cloud-init then parses and processes user data, if available and vendor data, if available.
The cloud-init runtime is written in python.
Installation
yum install cloud-init
Configuration
cloud-init configuration is maintained in a YAML-format file:
/etc/cloud/cloud.cfg
Additional files from /etc/cloud/cloud.cfg.d are read in lexical order.
Example
users:
- default
disable_root: 1
ssh_pwauth: 0
mount_default_fields: [~, ~, 'auto', 'defaults,nofail', '0', '2']
resize_rootfs_tmp: /dev
ssh_deletekeys: 0
ssh_genkeytypes: ~
syslog_fix_perms: ~
cloud_init_modules:
- migrator
- bootcmd
- write-files
- growpart
- resizefs
- rsyslog
- users-groups
- ssh
cloud_config_modules:
- mounts
- locale
- set-passwords
- yum-add-repo
- package-update-upgrade-install
- timezone
- puppet
- chef
- salt-minion
- mcollective
- disable-ec2-metadata
- runcmd
cloud_final_modules:
- rightscale_userdata
- scripts-per-once
- scripts-per-boot
- scripts-per-instance
- scripts-user
- ssh-authkey-fingerprints
- keys-to-console
- phone-home
- final-message
system_info:
default_user:
name: ec2-user
lock_passwd: true
gecos: Cloud User
groups: [wheel, adm, systemd-journal]
sudo: ["ALL=(ALL) NOPASSWD:ALL"]
shell: /bin/bash
distro: rhel
paths:
cloud_dir: /var/lib/cloud
templates_dir: /etc/cloud/templates
ssh_svcname: sshd
# vim:syntax=yaml
Concepts
Cloud Dir
The "cloud_dir" is configured in /etc/cloud/cloud.cfg. It is /var/lib/cloud by default.
.
├── data
│ ├── instance-id
│ ├── previous-datasource
│ ├── previous-hostname
│ ├── previous-instance-id
│ ├── result.json
│ ├── set-hostname
│ └── status.json
├── handlers
├── instance -> /var/lib/cloud/instances/i-03e84d220850fa423
├── instances
│ ├── i-021c7fbfb1924dac1
│ │ └── ...
│ └── i-03e84d220850fa423
│ ├── boot-finished
│ ├── cloud-config.txt
│ ├── datasource
│ ├── handlers
│ ├── obj.pkl
│ ├── scripts
│ ├── sem
│ │ ├── config_amazonlinux_repo_https
│ │ ├── config_disk_setup
│ │ ├── config_keys_to_console
│ │ ├── config_locale
│ │ ├── config_mounts
│ │ ├── config_package_update_upgrade_install
│ │ ├── config_phone_home
│ │ ├── config_power_state_change
│ │ ├── config_resolv_conf
│ │ ├── config_rsyslog
│ │ ├── config_runcmd
│ │ ├── config_scripts_per_instance
│ │ ├── config_scripts_user
│ │ ├── config_set_hostname
│ │ ├── config_set_passwords
│ │ ├── config_ssh
│ │ ├── config_ssh_authkey_fingerprints
│ │ ├── config_timezone
│ │ ├── config_users_groups
│ │ ├── config_write_files
│ │ ├── config_write_metadata
│ │ ├── config_yum_add_repo
│ │ ├── config_yum_configure
│ │ └── consume_data
│ ├── user-data.txt
│ ├── user-data.txt.i
│ ├── vendor-data.txt
│ └── vendor-data.txt.i
├── scripts
│ ├── per-boot
│ │ └── 050-someprogram-start.sh
│ ├── per-instance
│ ├── per-once
│ └── vendor
├── seed
└── sem
└── config_scripts_per_once.once
scripts/per-boot
This is where logic that must be executed on each boot goes.
Setting hostname
Done by the following modules, that work with systemd-hostnamed:
... cloud_init_modules: ... - set_hostname - update_hostname - update_etc_hosts ...