Introduce "sync-by-content" flag, implemented for secrets and configmaps (#352)

* Add initial "sync-by-content" mode

- Optionally ignore the "replicated-from-version" annotation and always compare by contents
- Implemented for secrets and config maps
- Add test for secrets for the new feature
- Change secret tests to use fake.Clientset instead of running in whatever happened to be your active KUBECONFIG(!)

* Refine the resource version updates in the fake client

* Remove WIP fake client usage

* Update README and mention new --sync-by-content flag

---------

Co-authored-by: Martin Helmich <m.helmich@mittwald.de>

Author: stippi2

README.md

@@ -157,6 +157,17 @@ data: {}
 The replicator will then copy the `data` attribute of the referenced object into the annotated object and keep them in
 sync.
 
+By default, the replicator adds an annotation `replicator.v1.mittwald.de/replicated-from-version` to the target object.
+This annotation contains the resource-version of the source object at the time of replication.
+
+##### Sync by Content
+
+When the target object is re-applied with an empty `data` attribute, the replicator will not automatically perform replication.
+The reason is that the target already has the `replicated-from-version` annotation with a matching source resource-version.
+For Secrets and ConfigMaps, there is the option to synchronize _based on the content_, ignoring the `replicated-from-version` annotation.
+
+To activate this mode, start the replicator with the `--sync-by-content` flag.
+
 #### Special case: TLS secrets
 
 Secrets of type `kubernetes.io/tls` are treated in a special way and need to have a `data["tls.crt"]` and a

config.go

@@ -15,4 +15,5 @@ type flags struct {
 	ReplicateRoles           bool
 	ReplicateRoleBindings    bool
 	ReplicateServiceAccounts bool
+	SyncByContent            bool
 }

go.mod

@@ -1,30 +1,33 @@
 module github.com/mittwald/kubernetes-replicator
 
-go 1.22
+go 1.22.0
+
+toolchain go1.23.0
 
 require (
 	github.com/hashicorp/go-multierror v1.1.1
 	github.com/pkg/errors v0.9.1
 	github.com/sirupsen/logrus v1.9.3
 	github.com/stretchr/testify v1.9.0
-	k8s.io/api v0.29.4
-	k8s.io/apimachinery v0.29.4
-	k8s.io/client-go v0.29.4
+	k8s.io/api v0.31.1
+	k8s.io/apimachinery v0.31.1
+	k8s.io/client-go v0.31.1
 )
 
 require (
-	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
 	github.com/emicklei/go-restful/v3 v3.11.0 // indirect
-	github.com/go-logr/logr v1.3.0 // indirect
+	github.com/fxamacker/cbor/v2 v2.7.0 // indirect
+	github.com/go-logr/logr v1.4.2 // indirect
 	github.com/go-openapi/jsonpointer v0.19.6 // indirect
 	github.com/go-openapi/jsonreference v0.20.2 // indirect
-	github.com/go-openapi/swag v0.22.3 // indirect
+	github.com/go-openapi/swag v0.22.4 // indirect
 	github.com/gogo/protobuf v1.3.2 // indirect
 	github.com/golang/protobuf v1.5.4 // indirect
 	github.com/google/gnostic-models v0.6.8 // indirect
 	github.com/google/go-cmp v0.6.0 // indirect
 	github.com/google/gofuzz v1.2.0 // indirect
-	github.com/google/uuid v1.3.0 // indirect
+	github.com/google/uuid v1.6.0 // indirect
 	github.com/hashicorp/errwrap v1.0.0 // indirect
 	github.com/imdario/mergo v0.3.7 // indirect
 	github.com/josharian/intern v1.0.0 // indirect
@@ -33,23 +36,24 @@ require (
 	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/modern-go/reflect2 v1.0.2 // indirect
 	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
-	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
 	github.com/spf13/pflag v1.0.5 // indirect
-	golang.org/x/net v0.23.0 // indirect
-	golang.org/x/oauth2 v0.10.0 // indirect
-	golang.org/x/sys v0.18.0 // indirect
-	golang.org/x/term v0.18.0 // indirect
-	golang.org/x/text v0.14.0 // indirect
+	github.com/x448/float16 v0.8.4 // indirect
+	golang.org/x/net v0.26.0 // indirect
+	golang.org/x/oauth2 v0.21.0 // indirect
+	golang.org/x/sys v0.21.0 // indirect
+	golang.org/x/term v0.21.0 // indirect
+	golang.org/x/text v0.16.0 // indirect
 	golang.org/x/time v0.3.0 // indirect
-	google.golang.org/appengine v1.6.7 // indirect
-	google.golang.org/protobuf v1.33.0 // indirect
+	google.golang.org/protobuf v1.34.2 // indirect
+	gopkg.in/evanphx/json-patch.v4 v4.12.0 // indirect
 	gopkg.in/inf.v0 v0.9.1 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
-	k8s.io/klog/v2 v2.110.1 // indirect
-	k8s.io/kube-openapi v0.0.0-20231010175941-2dd684a91f00 // indirect
-	k8s.io/utils v0.0.0-20230726121419-3b25d923346b // indirect
+	k8s.io/klog/v2 v2.130.1 // indirect
+	k8s.io/kube-openapi v0.0.0-20240228011516-70dd3763d340 // indirect
+	k8s.io/utils v0.0.0-20240711033017-18e509b52bc8 // indirect
 	sigs.k8s.io/json v0.0.0-20221116044647-bc3834ca7abd // indirect
 	sigs.k8s.io/structured-merge-diff/v4 v4.4.1 // indirect
-	sigs.k8s.io/yaml v1.3.0 // indirect
+	sigs.k8s.io/yaml v1.4.0 // indirect
 )

go.sum

@@ -36,6 +36,7 @@ func init() {
 	flag.BoolVar(&f.ReplicateRoles, "replicate-roles", true, "Enable replication of roles")
 	flag.BoolVar(&f.ReplicateRoleBindings, "replicate-role-bindings", true, "Enable replication of role bindings")
 	flag.BoolVar(&f.ReplicateServiceAccounts, "replicate-service-accounts", true, "Enable replication of service accounts")
+	flag.BoolVar(&f.SyncByContent, "sync-by-content", false, "Always compare the contents of source and target resources and force them to be the same")
 	flag.Parse()
 
 	switch strings.ToUpper(strings.TrimSpace(f.LogLevel)) {
@@ -88,13 +89,13 @@ func main() {
 	client = kubernetes.NewForConfigOrDie(config)
 
 	if f.ReplicateSecrets {
-		secretRepl := secret.NewReplicator(client, f.ResyncPeriod, f.AllowAll)
+		secretRepl := secret.NewReplicator(client, f.ResyncPeriod, f.AllowAll, f.SyncByContent)
 		go secretRepl.Run()
 		enabledReplicators = append(enabledReplicators, secretRepl)
 	}
 
 	if f.ReplicateConfigMaps {
-		configMapRepl := configmap.NewReplicator(client, f.ResyncPeriod, f.AllowAll)
+		configMapRepl := configmap.NewReplicator(client, f.ResyncPeriod, f.AllowAll, f.SyncByContent)
 		go configMapRepl.Run()
 		enabledReplicators = append(enabledReplicators, configMapRepl)
 	}

main.go

@@ -3,13 +3,14 @@ package common
 import (
 	"context"
 	"fmt"
-	"k8s.io/apimachinery/pkg/labels"
 	"reflect"
 	"regexp"
 	"strconv"
 	"strings"
 	"time"
 
+	"k8s.io/apimachinery/pkg/labels"
+
 	"github.com/hashicorp/go-multierror"
 	"github.com/pkg/errors"
 	log "github.com/sirupsen/logrus"
@@ -22,13 +23,14 @@ import (
 )
 
 type ReplicatorConfig struct {
-	Kind         string
-	Client       kubernetes.Interface
-	ResyncPeriod time.Duration
-	AllowAll     bool
-	ListFunc     cache.ListFunc
-	WatchFunc    cache.WatchFunc
-	ObjType      runtime.Object
+	Kind          string
+	Client        kubernetes.Interface
+	ResyncPeriod  time.Duration
+	AllowAll      bool
+	SyncByContent bool
+	ListFunc      cache.ListFunc
+	WatchFunc     cache.WatchFunc
+	ObjType       runtime.Object
 }
 
 type UpdateFuncs struct {
@@ -44,6 +46,7 @@ type GenericReplicator struct {
 	Controller cache.Controller
 
 	DependencyMap map[string]map[string]interface{}
+	DependentMap  map[string]string
 	UpdateFuncs   UpdateFuncs
 
 	// ReplicateToList is a set that caches the names of all secrets that have a
@@ -60,6 +63,7 @@ func NewGenericReplicator(config ReplicatorConfig) *GenericReplicator {
 	repl := GenericReplicator{
 		ReplicatorConfig:        config,
 		DependencyMap:           make(map[string]map[string]interface{}),
+		DependentMap:            make(map[string]string),
 		ReplicateToList:         GenericMap[string, struct{}]{},
 		ReplicateToMatchingList: GenericMap[string, labels.Selector]{},
 	}
@@ -257,6 +261,24 @@ func (r *GenericReplicator) ResourceAdded(obj interface{}) {
 			logger.WithError(err).Error("failed to update cache")
 		}
 	}
+	source, ok := r.DependentMap[sourceKey]
+	if ok {
+		logger.Debugf("objectMeta %s has source %s", sourceKey, source)
+
+		sourceObject, exists, err := r.Store.GetByKey(source)
+		if err != nil {
+			logger.Debugf("could not get source %s %s: %s", r.Kind, source, err)
+			return
+		} else if !exists {
+			logger.Debugf("could not get source %s %s: does not exist", r.Kind, source)
+			return
+		}
+		targetMap := map[string]interface{}{MustGetKey(obj): ""}
+		if err := r.updateDependents(sourceObject, targetMap); err != nil {
+			logger.WithError(err).
+				Errorf("Failed to update cache for %s: %v", MustGetKey(objectMeta), err)
+		}
+	}
 
 	annotations := objectMeta.GetAnnotations()
 
@@ -323,6 +345,10 @@ func (r *GenericReplicator) resourceAddedReplicateFrom(sourceLocation string, ta
 
 	r.DependencyMap[sourceLocation][cacheKey] = nil
 
+	if _, ok := r.DependentMap[cacheKey]; !ok {
+		r.DependentMap[cacheKey] = sourceLocation
+	}
+
 	sourceObject, exists, err := r.Store.GetByKey(sourceLocation)
 	if err != nil {
 		return errors.Wrapf(err, "Could not get source %s: %v", sourceLocation, err)

replicate/common/generic-replicator.go

@@ -1,6 +1,7 @@
 package configmap
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
 	"fmt"
@@ -25,14 +26,15 @@ type Replicator struct {
 }
 
 // NewReplicator creates a new config map replicator
-func NewReplicator(client kubernetes.Interface, resyncPeriod time.Duration, allowAll bool) common.Replicator {
+func NewReplicator(client kubernetes.Interface, resyncPeriod time.Duration, allowAll, syncByContent bool) common.Replicator {
 	repl := Replicator{
 		GenericReplicator: common.NewGenericReplicator(common.ReplicatorConfig{
-			Kind:         "ConfigMap",
-			ObjType:      &v1.ConfigMap{},
-			AllowAll:     allowAll,
-			ResyncPeriod: resyncPeriod,
-			Client:       client,
+			Kind:          "ConfigMap",
+			ObjType:       &v1.ConfigMap{},
+			AllowAll:      allowAll,
+			SyncByContent: syncByContent,
+			ResyncPeriod:  resyncPeriod,
+			Client:        client,
 			ListFunc: func(lo metav1.ListOptions) (runtime.Object, error) {
 				return client.CoreV1().ConfigMaps("").List(context.TODO(), lo)
 			},
@@ -65,7 +67,7 @@ func (r *Replicator) ReplicateDataFrom(sourceObj interface{}, targetObj interfac
 	targetVersion, ok := target.Annotations[common.ReplicatedFromVersionAnnotation]
 	sourceVersion := source.ResourceVersion
 
-	if ok && targetVersion == sourceVersion {
+	if ok && targetVersion == sourceVersion && !r.SyncByContent {
 		logger.Debugf("target %s is already up-to-date", common.MustGetKey(target))
 		return nil
 	}
@@ -78,17 +80,38 @@ func (r *Replicator) ReplicateDataFrom(sourceObj interface{}, targetObj interfac
 	prevKeys, hasPrevKeys := common.PreviouslyPresentKeys(&targetCopy.ObjectMeta)
 	replicatedKeys := make([]string, 0)
 
+	dataChanged := false
 	for key, value := range source.Data {
+		oldValue, ok := targetCopy.Data[key]
+		if ok {
+			if strings.Compare(value, oldValue) != 0 {
+				dataChanged = true
+			}
+		} else {
+			dataChanged = true
+		}
 		targetCopy.Data[key] = value
 
 		replicatedKeys = append(replicatedKeys, key)
 		delete(prevKeys, key)
 	}
 
 	if source.BinaryData != nil {
-		targetCopy.BinaryData = make(map[string][]byte)
+		if targetCopy.BinaryData == nil {
+			targetCopy.BinaryData = make(map[string][]byte)
+		}
 		for key, value := range source.BinaryData {
-			targetCopy.BinaryData[key] = value
+			newValue := make([]byte, len(value))
+			copy(newValue, value)
+			oldValue, ok := targetCopy.BinaryData[key]
+			if ok {
+				if bytes.Compare(newValue, oldValue) != 0 {
+					dataChanged = true
+				}
+			} else {
+				dataChanged = true
+			}
+			targetCopy.BinaryData[key] = newValue
 
 			replicatedKeys = append(replicatedKeys, key)
 			delete(prevKeys, key)
@@ -100,9 +123,15 @@ func (r *Replicator) ReplicateDataFrom(sourceObj interface{}, targetObj interfac
 			logger.Debugf("removing previously present key %s: not present in source any more", k)
 			delete(targetCopy.Data, k)
 			delete(targetCopy.BinaryData, k)
+			dataChanged = true
 		}
 	}
 
+	if !dataChanged {
+		logger.Debugf("target values of %s are already up-to-date", common.MustGetKey(target))
+		return nil
+	}
+
 	sort.Strings(replicatedKeys)
 
 	logger.Infof("updating config map %s/%s", target.Namespace, target.Name)

replicate/configmap/configmaps.go

@@ -1,6 +1,7 @@
 package secret
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
 	"fmt"
@@ -25,14 +26,15 @@ type Replicator struct {
 }
 
 // NewReplicator creates a new secret replicator
-func NewReplicator(client kubernetes.Interface, resyncPeriod time.Duration, allowAll bool) common.Replicator {
+func NewReplicator(client kubernetes.Interface, resyncPeriod time.Duration, allowAll, syncByContent bool) common.Replicator {
 	repl := Replicator{
 		GenericReplicator: common.NewGenericReplicator(common.ReplicatorConfig{
-			Kind:         "Secret",
-			ObjType:      &v1.Secret{},
-			AllowAll:     allowAll,
-			ResyncPeriod: resyncPeriod,
-			Client:       client,
+			Kind:          "Secret",
+			ObjType:       &v1.Secret{},
+			AllowAll:      allowAll,
+			SyncByContent: syncByContent,
+			ResyncPeriod:  resyncPeriod,
+			Client:        client,
 			ListFunc: func(lo metav1.ListOptions) (runtime.Object, error) {
 				return client.CoreV1().Secrets("").List(context.TODO(), lo)
 			},
@@ -69,7 +71,7 @@ func (r *Replicator) ReplicateDataFrom(sourceObj interface{}, targetObj interfac
 	targetVersion, ok := target.Annotations[common.ReplicatedFromVersionAnnotation]
 	sourceVersion := source.ResourceVersion
 
-	if ok && targetVersion == sourceVersion {
+	if ok && targetVersion == sourceVersion && !r.SyncByContent {
 		logger.Debugf("target %s is already up-to-date", common.MustGetKey(target))
 		return nil
 	}
@@ -82,9 +84,18 @@ func (r *Replicator) ReplicateDataFrom(sourceObj interface{}, targetObj interfac
 	prevKeys, hasPrevKeys := common.PreviouslyPresentKeys(&targetCopy.ObjectMeta)
 	replicatedKeys := make([]string, 0)
 
+	dataChanged := false
 	for key, value := range source.Data {
 		newValue := make([]byte, len(value))
 		copy(newValue, value)
+		oldValue, ok := targetCopy.Data[key]
+		if ok {
+			if bytes.Compare(newValue, oldValue) != 0 {
+				dataChanged = true
+			}
+		} else {
+			dataChanged = true
+		}
 		targetCopy.Data[key] = newValue
 
 		replicatedKeys = append(replicatedKeys, key)
@@ -95,9 +106,15 @@ func (r *Replicator) ReplicateDataFrom(sourceObj interface{}, targetObj interfac
 		for k := range prevKeys {
 			logger.Debugf("removing previously present key %s: not present in source any more", k)
 			delete(targetCopy.Data, k)
+			dataChanged = true
 		}
 	}
 
+	if !dataChanged {
+		logger.Debugf("target values of %s are already up-to-date", common.MustGetKey(target))
+		return nil
+	}
+
 	sort.Strings(replicatedKeys)
 
 	logger.Infof("updating target %s", common.MustGetKey(target))