Status: Experimental
We are developing a plugin system to kubebuilder, so that we can generate operators that follow other patterns.
While plugins remain experimental, you must pass the KUBEBUILDER_ENABLE_PLUGINS=1
environment variable to enable plugin functionality. (Any non-empty
value will work!)
When you specify KUBEBUILDER_ENABLE_PLUGINS=1, a flag --pattern will become
available for resource generation. Specifying --pattern=addon will change
resource code generation to generate code that follows the addon pattern, as
being developed in the
cluster-addons
subproject.
The pattern=addon plugin is intended to serve both as an example of a plugin,
and as a real-world use case for driving development of the plugin system. We
don't intend for the plugin system to become an emacs competitor, but it must be
sufficiently flexible to support the various patterns of operators that
kubebuilder will generate.
We intend for plugins to be packaged in a separate binary, which will be
executed by the kubebuilder main binary. Data will be piped to the binary via
stdin, and returned over stdout. The serialization format will likely either be
yaml or json (to be determined!).
While we are developing this functionality though, we are developing it using an
in-process golang interface named Plugin, defined in
pkg/plugin/scaffold/scaffold.go. The interface is a
simple single-method interface that is intended to mirror the data-in / data-out
approach that will be used when executing a plugin in a separate binary. When
we have more stability of the plugin, we intend to replace the in-process
implementation with a implementation that execs a plugin in a separate binary.
The approach being prototyped is that we pass a model of the full state of the
generation world to the Plugin, which returns the full state of the generation
world after making appropriate changes. We are starting to define a model
package which includes a Universe comprising the various Files that are
being generated, along with the inputs like the Boilerplate and the Resource
we are currently generating. A plugin can change the Contents of Files, or
add/remove Files entirely.