Replace kubectl with Go server-side apply

Signed-off-by: Stefan Prodan <stefan.prodan@gmail.com>

internal/utils/apply.go

@@ -0,0 +1,81 @@
+package utils
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"time"
+
+	"github.com/fluxcd/pkg/ssa"
+	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
+	"sigs.k8s.io/cli-utils/pkg/kstatus/polling"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+	"sigs.k8s.io/controller-runtime/pkg/client/apiutil"
+	"sigs.k8s.io/kustomize/api/konfig"
+
+	"github.com/fluxcd/flux2/pkg/manifestgen/kustomization"
+)
+
+// Apply is the equivalent of 'kubectl apply --server-side -f'.
+// If the given manifest is a kustomization.yaml, then apply performs the equivalent of 'kubectl apply --server-side -k'.
+func Apply(ctx context.Context, kubeConfigPath string, kubeContext string, manifestPath string) (string, error) {
+	cfg, err := KubeConfig(kubeConfigPath, kubeContext)
+	if err != nil {
+		return "", err
+	}
+	restMapper, err := apiutil.NewDynamicRESTMapper(cfg)
+	if err != nil {
+		return "", err
+	}
+	kubeClient, err := client.New(cfg, client.Options{Mapper: restMapper})
+	if err != nil {
+		return "", err
+	}
+	kubePoller := polling.NewStatusPoller(kubeClient, restMapper)
+
+	resourceManager := ssa.NewResourceManager(kubeClient, kubePoller, ssa.Owner{
+		Field: "flux",
+		Group: "fluxcd.io",
+	})
+
+	objs, err := readObjects(manifestPath)
+	if err != nil {
+		return "", err
+	}
+
+	if len(objs) < 1 {
+		return "", fmt.Errorf("no Kubernetes objects found at: %s", manifestPath)
+	}
+
+	changeSet, err := resourceManager.ApplyAllStaged(ctx, objs, false, time.Minute)
+	if err != nil {
+		return "", err
+	}
+
+	return changeSet.String(), nil
+}
+
+func readObjects(manifestPath string) ([]*unstructured.Unstructured, error) {
+	if _, err := os.Stat(manifestPath); err != nil {
+		return nil, err
+	}
+
+	if filepath.Base(manifestPath) == konfig.DefaultKustomizationFileName() {
+		resources, err := kustomization.Build(filepath.Dir(manifestPath))
+		if err != nil {
+			return nil, err
+		}
+		return ssa.ReadObjects(bytes.NewReader(resources))
+	}
+
+	ms, err := os.Open(manifestPath)
+	if err != nil {
+		return nil, err
+	}
+	defer ms.Close()
+
+	return ssa.ReadObjects(bufio.NewReader(ms))
+}