new driver: kubernetes

Tested with `kind` and GKE.

Note: "nodes" shown in `docker buildx ls` are unrelated to Kubernetes "nodes".
Probably buildx should come up with an alternative term.

Usage:

  $ kind create cluster
  $ export KUBECONFIG="$(kind get kubeconfig-path --name="kind")"

  $ docker buildx create --driver kubernetes --driver-opt replicas=3 --use
  $ docker buildx build -t foo --load .

`--load` loads the image into the local Docker.

Driver opts:

  - `image=IMAGE` - Sets the container image to be used for running buildkit.
  - `namespace=NS` - Sets the Kubernetes namespace. Defaults to the current namespace.
  - `replicas=N` - Sets the number of `Pod` replicas. Defaults to 1.
  - `rootless=(true|false)` - Run the container as a non-root user without `securityContext.privileged`. Defaults to false.
  - `loadbalance=(sticky|random)` - Load-balancing strategy. If set to "sticky", the pod is chosen using the hash of the context path. Defaults to "sticky"

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

vendor/k8s.io/apimachinery/pkg/api/meta/lazy.go

@@ -0,0 +1,104 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package meta
+
+import (
+	"sync"
+
+	"k8s.io/apimachinery/pkg/runtime/schema"
+)
+
+// lazyObject defers loading the mapper and typer until necessary.
+type lazyObject struct {
+	loader func() (RESTMapper, error)
+
+	lock   sync.Mutex
+	loaded bool
+	err    error
+	mapper RESTMapper
+}
+
+// NewLazyObjectLoader handles unrecoverable errors when creating a RESTMapper / ObjectTyper by
+// returning those initialization errors when the interface methods are invoked. This defers the
+// initialization and any server calls until a client actually needs to perform the action.
+func NewLazyRESTMapperLoader(fn func() (RESTMapper, error)) RESTMapper {
+	obj := &lazyObject{loader: fn}
+	return obj
+}
+
+// init lazily loads the mapper and typer, returning an error if initialization has failed.
+func (o *lazyObject) init() error {
+	o.lock.Lock()
+	defer o.lock.Unlock()
+	if o.loaded {
+		return o.err
+	}
+	o.mapper, o.err = o.loader()
+	o.loaded = true
+	return o.err
+}
+
+var _ RESTMapper = &lazyObject{}
+
+func (o *lazyObject) KindFor(resource schema.GroupVersionResource) (schema.GroupVersionKind, error) {
+	if err := o.init(); err != nil {
+		return schema.GroupVersionKind{}, err
+	}
+	return o.mapper.KindFor(resource)
+}
+
+func (o *lazyObject) KindsFor(resource schema.GroupVersionResource) ([]schema.GroupVersionKind, error) {
+	if err := o.init(); err != nil {
+		return []schema.GroupVersionKind{}, err
+	}
+	return o.mapper.KindsFor(resource)
+}
+
+func (o *lazyObject) ResourceFor(input schema.GroupVersionResource) (schema.GroupVersionResource, error) {
+	if err := o.init(); err != nil {
+		return schema.GroupVersionResource{}, err
+	}
+	return o.mapper.ResourceFor(input)
+}
+
+func (o *lazyObject) ResourcesFor(input schema.GroupVersionResource) ([]schema.GroupVersionResource, error) {
+	if err := o.init(); err != nil {
+		return []schema.GroupVersionResource{}, err
+	}
+	return o.mapper.ResourcesFor(input)
+}
+
+func (o *lazyObject) RESTMapping(gk schema.GroupKind, versions ...string) (*RESTMapping, error) {
+	if err := o.init(); err != nil {
+		return nil, err
+	}
+	return o.mapper.RESTMapping(gk, versions...)
+}
+
+func (o *lazyObject) RESTMappings(gk schema.GroupKind, versions ...string) ([]*RESTMapping, error) {
+	if err := o.init(); err != nil {
+		return nil, err
+	}
+	return o.mapper.RESTMappings(gk, versions...)
+}
+
+func (o *lazyObject) ResourceSingularizer(resource string) (singular string, err error) {
+	if err := o.init(); err != nil {
+		return "", err
+	}
+	return o.mapper.ResourceSingularizer(resource)
+}