POC: labels selector poc - failed

Makefile

@@ -36,7 +36,7 @@ build: $(CMD)
 .PHONY: $(CMD)
 $(CMD): %: $(BUILD_DEST)/%
 
-$(BUILD_DEST)/%: cmd/%
+$(BUILD_DEST)/%: clean cmd/%
 	go build $(GOTOOLFLAGS) -o $@ ./cmd/$*
 
 GOLANGCI_LINT = _tools/golangci-lint

deploy/crd/kcp.io/syncagent.kcp.io_publishedresources.yaml

@@ -318,6 +318,7 @@ spec:
                   type: object
                 related:
                   items:
+                    description: RelatedResourceSpec describes a related resource that should be synchronized
                     properties:
                       identifier:
                         description: |-
@@ -329,6 +330,50 @@ spec:
                       kind:
                         description: ConfigMap or Secret
                         type: string
+                      labelSelector:
+                        description: LabelSelector is used to filter the related resource in the service cluster.
+                        properties:
+                          matchExpressions:
+                            description: matchExpressions is a list of label selector requirements. The requirements are ANDed.
+                            items:
+                              description: |-
+                                A label selector requirement is a selector that contains values, a key, and an operator that
+                                relates the key and values.
+                              properties:
+                                key:
+                                  description: key is the label key that the selector applies to.
+                                  type: string
+                                operator:
+                                  description: |-
+                                    operator represents a key's relationship to a set of values.
+                                    Valid operators are In, NotIn, Exists and DoesNotExist.
+                                  type: string
+                                values:
+                                  description: |-
+                                    values is an array of string values. If the operator is In or NotIn,
+                                    the values array must be non-empty. If the operator is Exists or DoesNotExist,
+                                    the values array must be empty. This array is replaced during a strategic
+                                    merge patch.
+                                  items:
+                                    type: string
+                                  type: array
+                                  x-kubernetes-list-type: atomic
+                              required:
+                                - key
+                                - operator
+                              type: object
+                            type: array
+                            x-kubernetes-list-type: atomic
+                          matchLabels:
+                            additionalProperties:
+                              type: string
+                            description: |-
+                              matchLabels is a map of {key,value} pairs. A single {key,value} in the matchLabels
+                              map is equivalent to an element of matchExpressions, whose key field is "key", the
+                              operator is "In", and the values array contains only "value". The requirements are ANDed.
+                            type: object
+                        type: object
+                        x-kubernetes-map-type: atomic
                       mutation:
                         description: |-
                           Mutation configures optional transformation rules for the related resource.
@@ -411,6 +456,7 @@ spec:
                         description: '"service" or "kcp"'
                         type: string
                       reference:
+                        description: Reference to the related resource in the service cluster.
                         properties:
                           name:
                             properties:
@@ -453,8 +499,10 @@ spec:
                       - identifier
                       - kind
                       - origin
-                      - reference
                     type: object
+                    x-kubernetes-validations:
+                      - message: must specify exactly one of reference or labelSelector
+                        rule: (has(self.reference) && !has(self.labelSelector)) || (!has(self.reference) && has(self.labelSelector))
                   type: array
                 resource:
                   description: |-

internal/projection/naming.go

@@ -41,14 +41,7 @@ func GenerateLocalObjectName(pr *syncagentv1alpha1.PublishedResource, object met
 		naming = &syncagentv1alpha1.ResourceNaming{}
 	}
 
-	replacer := strings.NewReplacer(
-		// order of elements is important here, "$fooHash" needs to be defined before "$foo"
-		syncagentv1alpha1.PlaceholderRemoteClusterName, clusterName.String(),
-		syncagentv1alpha1.PlaceholderRemoteNamespaceHash, shortSha1Hash(object.GetNamespace()),
-		syncagentv1alpha1.PlaceholderRemoteNamespace, object.GetNamespace(),
-		syncagentv1alpha1.PlaceholderRemoteNameHash, shortSha1Hash(object.GetName()),
-		syncagentv1alpha1.PlaceholderRemoteName, object.GetName(),
-	)
+	replacer := getReplacer(object, clusterName)
 
 	result := types.NamespacedName{}
 
@@ -69,6 +62,33 @@ func GenerateLocalObjectName(pr *syncagentv1alpha1.PublishedResource, object met
 	return result
 }
 
+func GenerateLocalLabelSelector(pr *syncagentv1alpha1.RelatedResourceSpec, object metav1.Object, clusterName logicalcluster.Name) *metav1.LabelSelector {
+	replacer := getReplacer(object, clusterName)
+
+	result := metav1.LabelSelector{}
+
+	result.MatchLabels = map[string]string{}
+
+	for key, value := range pr.LabelSelector.MatchLabels {
+		result.MatchLabels[replacer.Replace(key)] = replacer.Replace(value)
+	}
+
+	// TODO: MatchExpressions are not yet supported with the current naming scheme.
+	result.MatchExpressions = pr.LabelSelector.MatchExpressions
+	return &result
+}
+
+func getReplacer(object metav1.Object, clusterName logicalcluster.Name) *strings.Replacer {
+	return strings.NewReplacer(
+		// order of elements is important here, "$fooHash" needs to be defined before "$foo"
+		syncagentv1alpha1.PlaceholderRemoteClusterName, clusterName.String(),
+		syncagentv1alpha1.PlaceholderRemoteNamespaceHash, shortSha1Hash(object.GetNamespace()),
+		syncagentv1alpha1.PlaceholderRemoteNamespace, object.GetNamespace(),
+		syncagentv1alpha1.PlaceholderRemoteNameHash, shortSha1Hash(object.GetName()),
+		syncagentv1alpha1.PlaceholderRemoteName, object.GetName(),
+	)
+}
+
 func shortSha1Hash(value string) string {
 	hash := sha1.New()
 	if _, err := hash.Write([]byte(value)); err != nil {

internal/sync/syncer_related.go

@@ -25,7 +25,9 @@ import (
 	"go.uber.org/zap"
 
 	"github.com/kcp-dev/api-syncagent/internal/mutation"
+	"github.com/kcp-dev/api-syncagent/internal/projection"
 	syncagentv1alpha1 "github.com/kcp-dev/api-syncagent/sdk/apis/syncagent/v1alpha1"
+	"github.com/kcp-dev/logicalcluster/v3"
 
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
@@ -70,10 +72,42 @@ func (s *ResourceSyncer) processRelatedResource(log *zap.SugaredLogger, stateSto
 		dest = local
 	}
 
-	// to find the source related object, we first need to determine its name/namespace
-	sourceKey, err := resolveResourceReference(source.object, relRes.Reference)
-	if err != nil {
-		return false, fmt.Errorf("failed to determine related object's source key: %w", err)
+	var sourceKey *ctrlruntimeclient.ObjectKey
+	switch {
+	case relRes.Reference != nil:
+		// to find the source related object, we first need to determine its name/namespace
+		sourceKey, err = resolveResourceReference(source.object, *relRes.Reference)
+		if err != nil {
+			return false, fmt.Errorf("failed to determine related object's source key: %w", err)
+		}
+	case relRes.LabelSelector != nil:
+		// if no reference is given, we can use a label selector to find the source object
+		sourceObjs := &unstructured.UnstructuredList{}
+		sourceObjs.SetAPIVersion("v1")
+		sourceObjs.SetKind(relRes.Kind)
+
+		// TODO: would need to handle replacer here as well to select right object.
+		cn, ok := source.object.GetLabels()[remoteObjectClusterLabel]
+		if !ok {
+			return false, fmt.Errorf("missing cluster label on source object")
+		}
+		clusterName := logicalcluster.Name(cn)
+		labels := projection.GenerateLocalLabelSelector(&relRes, source.object, clusterName)
+
+		if err := source.client.List(source.ctx, sourceObjs, ctrlruntimeclient.MatchingLabels(labels.MatchLabels)); err != nil {
+			return false, fmt.Errorf("failed to list related objects: %w", err)
+		}
+		if len(sourceObjs.Items) == 0 {
+			return false, nil
+		}
+		if len(sourceObjs.Items) > 1 {
+			// HACK: we take first one, as we can't select multiple objects or by name only!
+			log.Warnw("found multiple related objects, taking first one", "count", len(sourceObjs.Items))
+		}
+		sourceKey = &ctrlruntimeclient.ObjectKey{
+			Namespace: sourceObjs.Items[0].GetNamespace(),
+			Name:      sourceObjs.Items[0].GetName(),
+		}
 	}
 
 	// find the source related object
@@ -92,9 +126,18 @@ func (s *ResourceSyncer) processRelatedResource(log *zap.SugaredLogger, stateSto
 	}
 
 	// do the same to find the destination object
-	destKey, err := resolveResourceReference(dest.object, relRes.Reference)
-	if err != nil {
-		return false, fmt.Errorf("failed to determine related object's destination key: %w", err)
+	var destKey *ctrlruntimeclient.ObjectKey
+	switch {
+	case relRes.Reference != nil:
+		destKey, err = resolveResourceReference(dest.object, *relRes.Reference)
+		if err != nil {
+			return false, fmt.Errorf("failed to determine related object's destination key: %w", err)
+		}
+	case relRes.LabelSelector != nil:
+		destKey = &ctrlruntimeclient.ObjectKey{
+			Namespace: sourceObj.GetNamespace(),
+			Name:      sourceObj.GetName(),
+		}
 	}
 
 	destObj := &unstructured.Unstructured{}

sdk/apis/syncagent/v1alpha1/published_resource.go

@@ -158,6 +158,8 @@ type ResourceTemplateMutation struct {
 	Template string `json:"template"`
 }
 
+// +kubebuilder:validation:XValidation:rule="(has(self.reference) && !has(self.labelSelector)) || (!has(self.reference) && has(self.labelSelector))",message="must specify exactly one of reference or labelSelector"
+// RelatedResourceSpec describes a related resource that should be synchronized
 type RelatedResourceSpec struct {
 	// Identifier is a unique name for this related resource. The name must be unique within one
 	// PublishedResource and is the key by which consumers (end users) can identify and consume the
@@ -171,7 +173,11 @@ type RelatedResourceSpec struct {
 	// ConfigMap or Secret
 	Kind string `json:"kind"`
 
-	Reference RelatedResourceReference `json:"reference"`
+	// Reference to the related resource in the service cluster.
+	Reference *RelatedResourceReference `json:"reference,omitempty"`
+
+	// LabelSelector is used to filter the related resource in the service cluster.
+	LabelSelector *metav1.LabelSelector `json:"labelSelector,omitempty"`
 
 	// Mutation configures optional transformation rules for the related resource.
 	// Status mutations are only performed when the related resource originates in kcp.