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adding_resources.md

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Adding resources

Resources live under pkg/apis/<group>/<version>/<resource>_types.go. It is recommended to use apiserver-boot to create new groups, versions, and resources.

Creating a resource with apiserver-boot

Provide your domain + the api group and version + the resource Kind. The resource name will be the pluralized lowercased kind.

apiserver-boot create group version resource --group <group> --version <version> --kind <Kind>

Add --with-status-subresource=false option, if your resource is stateless.

Anatomy of a resource

A resource has a go struct which defines the Kind schema, and is annotated with comment directives used by the code generator to wire the storage and REST endpoints.

Example:

var _ resource.Object = &Foo{}
var _ resourcestrategy.Validater = &Foo{}

// +genclient=true
// +k8s:deepcopy-gen:interfaces=k8s.io/apimachinery/pkg/runtime.Object

// +k8s:openapi-gen=true
// Foo defines some thing
type Foo struct {
	metav1.TypeMeta   `json:",inline"`
	metav1.ObjectMeta `json:"metadata,omitempty"`

    // spec defines the desired state of Foo
	Spec   FooSpec   `json:"spec,omitempty"`

    // status records the observed state of Foo
	Status FooStatus `json:"status,omitempty"`
}

// FooSpec defines the desired state of Foo
type FooSpec struct {
    // some_spec_field defines some desired state about Foo
	SomeSpecField int `json:"some_spec_field,omitempty"`
}

var _ resource.ObjectWithStatusSubResource = &Foo{}
var _ resource.StatusSubResource = &FooStatus{}

// FooStatus records the observed state of Foo
type FooStatus struct {
	// some_status_field records some observed state about Foo
	SomeStatusField int `json:"some_status_field,omitempty"`
}

Breakdown of example

var _ resource.Object = &Foo{}

This line ensures the resource implements resource.Object from apiserver-runtime so that it can be served in the apiserver.

var _ resourcestrategy.Validater = &Foo{}

This tells the apiserver-runtime the resource has a custom validation function which is called before we writing the resource into storage.

type Foo struct {...}

This block defines the resource schema

metav1.TypeMeta   `json:",inline"`
metav1.ObjectMeta `json:"metadata,omitempty"`

These define metadata common to most resources - such as the name, group/version/kind, annotations, and labels.

// spec defines the desired state of Foo
Spec   FooSpec   `json:"spec,omitempty"`

This field defines the desired state of Foo that the controller loops will work towards.

// status records the observed state of Foo
Status FooStatus `json:"status,omitempty"`

This field records the state of Foo observed by the controller loops for clients to read.

// FooSpec defines the desired state of Foo
type FooSpec struct {
    // some_spec_field defines some desired state about Foo
	SomeSpecField int `json:"some_spec_field,omitempty"`
}

// FooStatus records the observed state of Foo
type FooStatus struct {
	// some_status_field records some observed state about Foo
	SomeStatusField int `json:"some_status_field,omitempty"`
}

These structures define the schema for the desired and observed state.

var _ resource.ObjectWithStatusSubResource = &Foo{}
var _ resource.StatusSubResource = &FooStatus{}

These lines ensure that the resource its status subresource, and defines the behaviod of the status subresource.

Controller

The controller reuses the kubebuilder's scaffolding, read this doc for more detailed information.