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>

driver/kubernetes/factory.go

@@ -0,0 +1,146 @@
+package kubernetes
+
+import (
+	"context"
+	"strconv"
+	"strings"
+
+	"github.com/docker/buildx/driver"
+	"github.com/docker/buildx/driver/bkimage"
+	"github.com/docker/buildx/driver/kubernetes/manifest"
+	"github.com/docker/buildx/driver/kubernetes/podchooser"
+	dockerclient "github.com/docker/docker/client"
+	"github.com/pkg/errors"
+	"k8s.io/client-go/kubernetes"
+)
+
+const prioritySupported = 30
+const priorityUnsupported = 70
+
+func init() {
+	driver.Register(&factory{})
+}
+
+type factory struct {
+}
+
+func (*factory) Name() string {
+	return DriverName
+}
+
+func (*factory) Usage() string {
+	return DriverName
+}
+
+func (*factory) Priority(ctx context.Context, api dockerclient.APIClient) int {
+	if api == nil {
+		return priorityUnsupported
+	}
+	return prioritySupported
+}
+
+func (f *factory) New(ctx context.Context, cfg driver.InitConfig) (driver.Driver, error) {
+	if cfg.KubeClientConfig == nil {
+		return nil, errors.Errorf("%s driver requires kubernetes API access", DriverName)
+	}
+	deploymentName, err := buildxNameToDeploymentName(cfg.Name)
+	if err != nil {
+		return nil, err
+	}
+	namespace, _, err := cfg.KubeClientConfig.Namespace()
+	if err != nil {
+		return nil, errors.Wrap(err, "cannot determine Kubernetes namespace, specify manually")
+	}
+	restClientConfig, err := cfg.KubeClientConfig.ClientConfig()
+	if err != nil {
+		return nil, err
+	}
+	clientset, err := kubernetes.NewForConfig(restClientConfig)
+	if err != nil {
+		return nil, err
+	}
+	d := &Driver{
+		factory:    f,
+		InitConfig: cfg,
+		clientset:  clientset,
+	}
+	deploymentOpt := &manifest.DeploymentOpt{
+		Name:          deploymentName,
+		Image:         bkimage.DefaultImage,
+		Replicas:      1,
+		BuildkitFlags: cfg.BuildkitFlags,
+		Rootless:      false,
+	}
+	loadbalance := LoadbalanceSticky
+	imageOverride := ""
+	for k, v := range cfg.DriverOpts {
+		switch k {
+		case "image":
+			imageOverride = v
+		case "namespace":
+			namespace = v
+		case "replicas":
+			deploymentOpt.Replicas, err = strconv.Atoi(v)
+			if err != nil {
+				return nil, err
+			}
+		case "rootless":
+			deploymentOpt.Rootless, err = strconv.ParseBool(v)
+			if err != nil {
+				return nil, err
+			}
+			deploymentOpt.Image = bkimage.DefaultRootlessImage
+		case "loadbalance":
+			switch v {
+			case LoadbalanceSticky:
+			case LoadbalanceRandom:
+			default:
+				return nil, errors.Errorf("invalid loadbalance %q", v)
+			}
+			loadbalance = v
+		default:
+			return nil, errors.Errorf("invalid driver option %s for driver %s", k, DriverName)
+		}
+	}
+	if imageOverride != "" {
+		deploymentOpt.Image = imageOverride
+	}
+	d.deployment, err = manifest.NewDeployment(deploymentOpt)
+	if err != nil {
+		return nil, err
+	}
+	d.minReplicas = deploymentOpt.Replicas
+	d.deploymentClient = clientset.AppsV1().Deployments(namespace)
+	d.podClient = clientset.CoreV1().Pods(namespace)
+	switch loadbalance {
+	case LoadbalanceSticky:
+		d.podChooser = &podchooser.StickyPodChooser{
+			Key:        cfg.ContextPathHash,
+			PodClient:  d.podClient,
+			Deployment: d.deployment,
+		}
+	case LoadbalanceRandom:
+		d.podChooser = &podchooser.RandomPodChooser{
+			PodClient:  d.podClient,
+			Deployment: d.deployment,
+		}
+	}
+	return d, nil
+}
+
+func (f *factory) AllowsInstances() bool {
+	return true
+}
+
+// buildxNameToDeploymentName converts buildx name to Kubernetes Deployment name.
+//
+// eg. "buildx_buildkit_loving_mendeleev0" -> "loving-mendeleev0"
+func buildxNameToDeploymentName(bx string) (string, error) {
+	// TODO: commands.util.go should not pass "buildx_buildkit_" prefix to drivers
+	if !strings.HasPrefix(bx, "buildx_buildkit_") {
+		return "", errors.Errorf("expected a string with \"buildx_buildkit_\", got %q", bx)
+	}
+	s := strings.TrimPrefix(bx, "buildx_buildkit_")
+	s = strings.ReplaceAll(s, "_", "-")
+	return s, nil
+}