feat: Implement Server-Side Diffs

Signed-off-by: Leonardo Luz Almeida <[email protected]>

Author: leoluz

pkg/cache/cluster.go

@@ -119,6 +119,8 @@ type ClusterCache interface {
 	OnResourceUpdated(handler OnResourceUpdatedHandler) Unsubscribe
 	// OnEvent register event handler that is executed every time when new K8S event received
 	OnEvent(handler OnEventHandler) Unsubscribe
+
+	GetKubectl() kube.Kubectl
 }
 
 type WeightedSemaphore interface {
@@ -303,6 +305,10 @@ func (c *clusterCache) GetGVKParser() *managedfields.GvkParser {
 	return c.gvkParser
 }
 
+func (c *clusterCache) GetKubectl() kube.Kubectl {
+	return c.kubectl
+}
+
 func (c *clusterCache) appendAPIResource(info kube.APIResourceInfo) {
 	exists := false
 	for i := range c.apiResources {

pkg/diff/diff.go

@@ -6,6 +6,7 @@ package diff
 
 import (
 	"bytes"
+	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -20,6 +21,7 @@ import (
 	"k8s.io/apimachinery/pkg/util/managedfields"
 	"k8s.io/apimachinery/pkg/util/strategicpatch"
 	"k8s.io/client-go/kubernetes/scheme"
+	cmdutil "k8s.io/kubectl/pkg/cmd/util"
 	"sigs.k8s.io/structured-merge-diff/v4/fieldpath"
 	"sigs.k8s.io/structured-merge-diff/v4/merge"
 	"sigs.k8s.io/structured-merge-diff/v4/typed"
@@ -83,6 +85,14 @@ func Diff(config, live *unstructured.Unstructured, opts ...Option) (*DiffResult,
 		Normalize(live, opts...)
 	}
 
+	if o.serverSideDiff {
+		r, err := ServerSideDiff(config, live, o.manager, o.kubeApplier, opts...)
+		if err != nil {
+			return nil, fmt.Errorf("error calculating server side diff: %w", err)
+		}
+		return r, nil
+	}
+
 	// TODO The two variables bellow are necessary because there is a cyclic
 	// dependency with the kube package that blocks the usage of constants
 	// from common package. common package needs to be refactored and exclude
@@ -120,6 +130,47 @@ func Diff(config, live *unstructured.Unstructured, opts ...Option) (*DiffResult,
 	return TwoWayDiff(config, live)
 }
 
+func ServerSideDiff(config, live *unstructured.Unstructured, manager string, kubeApplier KubeApplier, opts ...Option) (*DiffResult, error) {
+	if live != nil && config != nil {
+		return serverSideDiff(config, live, manager, kubeApplier, opts...)
+	}
+	return handleResourceCreateOrDeleteDiff(config, live)
+}
+
+func serverSideDiff(config, live *unstructured.Unstructured, manager string, kubeApplier KubeApplier, opts ...Option) (*DiffResult, error) {
+	predictedLiveStr, err := kubeApplier.ApplyResource(context.Background(), config, cmdutil.DryRunServer, false, false, true, manager)
+	if err != nil {
+		return nil, fmt.Errorf("error running server side apply in dryrun mode: %w", err)
+	}
+	predictedLive, err := jsonStrToUnstructured(predictedLiveStr)
+	if err != nil {
+		return nil, fmt.Errorf("error converting json string to unstructured: %w", err)
+	}
+
+	Normalize(predictedLive, opts...)
+
+	predictedLiveBytes, err := json.Marshal(predictedLive)
+	if err != nil {
+		return nil, fmt.Errorf("error marshaling predicted live resource: %w", err)
+	}
+
+	unstructured.RemoveNestedField(live.Object, "metadata", "managedFields")
+	liveBytes, err := json.Marshal(live)
+	if err != nil {
+		return nil, fmt.Errorf("error marshaling live resource: %w", err)
+	}
+	return buildDiffResult(predictedLiveBytes, liveBytes), nil
+}
+
+func jsonStrToUnstructured(jsonString string) (*unstructured.Unstructured, error) {
+	res := make(map[string]interface{})
+	err := json.Unmarshal([]byte(jsonString), &res)
+	if err != nil {
+		return nil, fmt.Errorf("unmarshal error: %s", err)
+	}
+	return &unstructured.Unstructured{Object: res}, nil
+}
+
 // StructuredMergeDiff will calculate the diff using the structured-merge-diff
 // k8s library (https://github.com/kubernetes-sigs/structured-merge-diff).
 func StructuredMergeDiff(config, live *unstructured.Unstructured, gvkParser *managedfields.GvkParser, manager string) (*DiffResult, error) {

pkg/diff/diff_options.go

@@ -1,9 +1,13 @@
 package diff
 
 import (
+	"context"
+
 	"github.com/go-logr/logr"
+	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 	"k8s.io/apimachinery/pkg/util/managedfields"
 	"k8s.io/klog/v2/klogr"
+	cmdutil "k8s.io/kubectl/pkg/cmd/util"
 )
 
 type Option func(*options)
@@ -17,6 +21,8 @@ type options struct {
 	structuredMergeDiff   bool
 	gvkParser             *managedfields.GvkParser
 	manager               string
+	serverSideDiff        bool
+	kubeApplier           KubeApplier
 }
 
 func applyOptions(opts []Option) options {
@@ -31,6 +37,10 @@ func applyOptions(opts []Option) options {
 	return o
 }
 
+type KubeApplier interface {
+	ApplyResource(ctx context.Context, obj *unstructured.Unstructured, dryRunStrategy cmdutil.DryRunStrategy, force, validate, serverSideApply bool, manager string) (string, error)
+}
+
 func IgnoreAggregatedRoles(ignore bool) Option {
 	return func(o *options) {
 		o.ignoreAggregatedRoles = ignore
@@ -66,3 +76,15 @@ func WithManager(manager string) Option {
 		o.manager = manager
 	}
 }
+
+func WithServerSideDiff(ssd bool) Option {
+	return func(o *options) {
+		o.serverSideDiff = ssd
+	}
+}
+
+func WithKubeApplier(ka KubeApplier) Option {
+	return func(o *options) {
+		o.kubeApplier = ka
+	}
+}

pkg/utils/kube/resource_ops.go

@@ -292,9 +292,16 @@ func (k *kubectlResourceOperations) newApplyOptions(ioStreams genericclioptions.
 				return nil, err
 			}
 		case cmdutil.DryRunServer:
-			err = o.PrintFlags.Complete("%s (server dry run)")
-			if err != nil {
-				return nil, err
+			// TODO (SSD): This logic should be refactored. PrintFlags should be
+			// configurable by the caller.
+			if serverSideApply {
+				o.PrintFlags.JSONYamlPrintFlags.ShowManagedFields = false
+				return o.PrintFlags.JSONYamlPrintFlags.ToPrinter("json")
+			} else {
+				err = o.PrintFlags.Complete("%s (server dry run)")
+				if err != nil {
+					return nil, err
+				}
 			}
 		}
 		return o.PrintFlags.ToPrinter()
@@ -312,6 +319,10 @@ func (k *kubectlResourceOperations) newApplyOptions(ioStreams genericclioptions.
 	return o, nil
 }
 
+func toPointer(str string) *string {
+	return &str
+}
+
 func (k *kubectlResourceOperations) newCreateOptions(config *rest.Config, ioStreams genericclioptions.IOStreams, fileName string, dryRunStrategy cmdutil.DryRunStrategy) (*create.CreateOptions, error) {
 	o := create.NewCreateOptions(ioStreams)