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/podchooser/podchooser.go

@@ -0,0 +1,97 @@
+package podchooser
+
+import (
+	"context"
+	"math/rand"
+	"sort"
+	"time"
+
+	"github.com/serialx/hashring"
+	"github.com/sirupsen/logrus"
+	appsv1 "k8s.io/api/apps/v1"
+	corev1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	clientcorev1 "k8s.io/client-go/kubernetes/typed/core/v1"
+)
+
+type PodChooser interface {
+	ChoosePod(ctx context.Context) (*corev1.Pod, error)
+}
+
+type RandomPodChooser struct {
+	RandSource rand.Source
+	PodClient  clientcorev1.PodInterface
+	Deployment *appsv1.Deployment
+}
+
+func (pc *RandomPodChooser) ChoosePod(ctx context.Context) (*corev1.Pod, error) {
+	pods, err := ListRunningPods(pc.PodClient, pc.Deployment)
+	if err != nil {
+		return nil, err
+	}
+	randSource := pc.RandSource
+	if randSource == nil {
+		randSource = rand.NewSource(time.Now().Unix())
+	}
+	rnd := rand.New(randSource)
+	n := rnd.Int() % len(pods)
+	logrus.Debugf("RandomPodChooser.ChoosePod(): len(pods)=%d, n=%d", len(pods), n)
+	return pods[n], nil
+}
+
+type StickyPodChooser struct {
+	Key        string
+	PodClient  clientcorev1.PodInterface
+	Deployment *appsv1.Deployment
+}
+
+func (pc *StickyPodChooser) ChoosePod(ctx context.Context) (*corev1.Pod, error) {
+	pods, err := ListRunningPods(pc.PodClient, pc.Deployment)
+	if err != nil {
+		return nil, err
+	}
+	var podNames []string
+	podMap := make(map[string]*corev1.Pod, len(pods))
+	for _, pod := range pods {
+		podNames = append(podNames, pod.Name)
+		podMap[pod.Name] = pod
+	}
+	ring := hashring.New(podNames)
+	chosen, ok := ring.GetNode(pc.Key)
+	if !ok {
+		// NOTREACHED
+		logrus.Errorf("no pod found for key %q", pc.Key)
+		rpc := &RandomPodChooser{
+			PodClient:  pc.PodClient,
+			Deployment: pc.Deployment,
+		}
+		return rpc.ChoosePod(ctx)
+	}
+	return podMap[chosen], nil
+}
+
+func ListRunningPods(client clientcorev1.PodInterface, depl *appsv1.Deployment) ([]*corev1.Pod, error) {
+	selector, err := metav1.LabelSelectorAsSelector(depl.Spec.Selector)
+	if err != nil {
+		return nil, err
+	}
+	listOpts := metav1.ListOptions{
+		LabelSelector: selector.String(),
+	}
+	podList, err := client.List(listOpts)
+	if err != nil {
+		return nil, err
+	}
+	var runningPods []*corev1.Pod
+	for i := range podList.Items {
+		pod := &podList.Items[i]
+		if pod.Status.Phase == corev1.PodRunning {
+			logrus.Debugf("pod runnning: %q", pod.Name)
+			runningPods = append(runningPods, pod)
+		}
+	}
+	sort.Slice(runningPods, func(i, j int) bool {
+		return runningPods[i].Name < runningPods[j].Name
+	})
+	return runningPods, nil
+}