Cloud-init is a tool that allows users to customize the configuration and behavior of cloud instances during the boot process. Cloud-init can process different kinds of data that are passed to the instance via user-data, which is a mechanism provided by various cloud providers to inject data into the instance. Among the kinds of data that cloud-init can process directly from user-data are:
Shell scripts to execute: Cloud-init can execute user-data that is formatted as a shell script, starting with the #!/bin/sh or #!/bin/bash shebang. The script can contain any commands that are valid in the shell environment of the instance. The script is executed as the root user during the boot process12.
Lists of URLs to import: Cloud-init can import user-data that is formatted as a list of URLs, separated by newlines. The URLs can point to any valid data source that cloud-init supports, such as shell scripts, cloud-config files, or include files. The URLs are fetched and processed by cloud-init in the order they appear in the list13.
cloud-config declarations in YAML: Cloud-init can process user-data that is formatted as a cloud-config file, which is a YAML document that contains declarations for various cloud-init modules. The cloud-config file can specify various aspects of the instance configuration, such as hostname, users, packages, commands, services, and more. The cloud-config file must start with the #cloud-config header14.
The other kinds of data listed in the question are not directly processed by cloud-init from user-data. They are either not supported, not recommended, or require additional steps to be processed. These kinds of data are:
ISO images to boot from: Cloud-init does not support booting from ISO images that are passed as user-data. ISO images are typically used to install an operating system on a physical or virtual machine, not to customize an existing cloud instance. To boot from an ISO image, the user would need to attach it as a secondary disk to the instance and configure the boot order accordingly5.
Base64-encoded binary files to execute: Cloud-init does not recommend passing binary files as user-data, as they may not be compatible with the instance’s architecture or operating system. Base64-encoding does not change this fact, as it only converts the binary data into ASCII characters. To execute a binary file, the user would need to decode it and make it executable on the instance6.
References:
User-Data Formats — cloud-init 22.1 documentation
User-Data Scripts
Include File
Cloud Config
How to Boot From ISO Image File Directly in Windows
How to run a binary file as a command in the terminal?.
