Internally, cloud-init builds a single configuration that is then referenced throughout the life of cloud-init. The configuration is built from multiple sources such that if a key is defined in multiple sources, the higher priority source overwrites the lower priority source.
From lowest priority to highest, configuration sources are:
Hardcoded config: Config that lives within the source of cloud-init and cannot be changed.
Configuration directory: Anything defined in
Runtime config: Anything defined in
Kernel command line: On the kernel command line, anything found between
end_ccwill be interpreted as cloud-config user data.
These four sources make up the base configuration.
Vendor and User Data#
Added to the base configuration are:
These get fetched from the datasource and are defined at instance launch.
While much of what is defined in the base configuration can be overridden by vendor data and user data, base configuration sources do not conform to #cloud-config
Network configuration happens independently from other cloud-init configuration. See network configuration documentation for more information.
Pass user data to the cloud provider. Every platform supporting cloud-init will provide a method of supplying user data. If you’re unsure how to do this, reference the documentation provided by the cloud platform you’re on. Additionally, there may be related cloud-init documentation in the datasource section.
Once an instance has been initialized, the user data may not be edited. It is sourced directly from the cloud, so even if you find a local file that contains user data, it will likely be overwritten next boot.
Modify the base config. This often involves submitting a PR to modify
the base cloud.cfg template, which is used to customize
/etc/cloud/cloud.cfg per distro. Additionally, a file can be added to
/etc/cloud/cloud.cfg.d to override a piece of the base configuration.
Pass vendor data. This is the preferred method for clouds to provide their own customization. In some cases, it may make sense to modify the base config in the same manner as distro providers on cloud-supported images.