cloudconfig

Cloud-config, often referred to as cloud-config, is a YAML-based configuration format used by cloud-init to provision cloud instances during their first boot. It provides a portable way to describe the initial state of a machine, including user accounts, installed packages, file content, and service configuration. Cloud-config is widely supported by major cloud platforms such as AWS, Google Cloud, Microsoft Azure, OpenStack, and various private clouds.

A cloud-config document is typically supplied as user-data and commonly starts with a directive such as '#cloud-config'. The content is written in YAML and may include sections such as users, ssh_authorized_keys, package_update, package_upgrade, packages, write_files, runcmd, and bootcmd. The users section can define login names, home directories, and sudo privileges; ssh_authorized_keys adds public keys for authentication. The packages and package_update keys drive package installation and updates, while write_files enables creation or modification of files on the instance. The runcmd and bootcmd sections specify commands to run during provisioning or early in boot, respectively. Networking can also be configured, depending on cloud-init version and provider.

During boot, cloud-init reads the provided cloud-config data from a suitable data source (for example a cloud metadata service, an attached NoCloud ISO, or a vendor-specific source) and executes the configured modules. The goal is to produce a consistent, automated initial setup that persists through the instance’s first boot.

Cloud-config is part of the cloud-init project and is periodically updated. Some keys may vary in availability across Linux distributions and cloud-init versions, so validation against the target environment is recommended.