storage, etcd3: add an option for configuring interval of compaction requests from apiserver

This commit adds an option for controlling request of compaction to
etcd3 from apiserver. There is a situation that apiserver cannot fully
own its etcd cluster (e.g. sharing it with canal). In such a case,
apiserver should have limited access in terms of etcd's auth
functionality so it don't have a priviledge to issue compaction
requests. It means that the compaction requests should be issued by
other component and apiserver's compaction requests are needless.

For such use cases, this commit adds a new flag
`storagebackend.Config.CompactionInterval`. If the flag is non 0,
apiserver issues the compaction requests like current behaviour (the
default is 5 minutes). If it is 0, apiserver doesn't issue the
requests. It can be configured with a newly added option of apiserver
`--etcd-compaction-interval`.

Kubernetes-commit: 87d4d3e92be6b93517f189082b0451cee6957ee5

pkg/server/options/etcd.go

@@ -148,6 +148,10 @@ func (s *EtcdOptions) AddFlags(fs *pflag.FlagSet) {
 
 	fs.StringVar(&s.EncryptionProviderConfigFilepath, "experimental-encryption-provider-config", s.EncryptionProviderConfigFilepath,
 		"The file containing configuration for encryption providers to be used for storing secrets in etcd")
+
+	fs.DurationVar(&s.StorageConfig.CompactionInterval, "etcd-compaction-interval", s.StorageConfig.CompactionInterval,
+		"The interval of compaction requests. If 0, the compaction request from apiserver is disabled.")
+
 }
 
 func (s *EtcdOptions) ApplyTo(c *server.Config) error {

pkg/storage/etcd3/compact.go

@@ -27,8 +27,7 @@ import (
 )
 
 const (
-	compactInterval = 5 * time.Minute
-	compactRevKey   = "compact_rev_key"
+	compactRevKey = "compact_rev_key"
 )
 
 var (
@@ -44,7 +43,7 @@ func init() {
 // By default, we save the most recent 10 minutes data and compact versions > 10minutes ago.
 // It should be enough for slow watchers and to tolerate burst.
 // TODO: We might keep a longer history (12h) in the future once storage API can take advantage of past version of keys.
-func StartCompactor(ctx context.Context, client *clientv3.Client) {
+func StartCompactor(ctx context.Context, client *clientv3.Client, compactInterval time.Duration) {
 	endpointsMapMu.Lock()
 	defer endpointsMapMu.Unlock()
 
@@ -60,7 +59,9 @@ func StartCompactor(ctx context.Context, client *clientv3.Client) {
 		endpointsMap[ep] = struct{}{}
 	}
 
-	go compactor(ctx, client, compactInterval)
+	if compactInterval != 0 {
+		go compactor(ctx, client, compactInterval)
+	}
 }
 
 // compactor periodically compacts historical versions of keys in etcd.

pkg/storage/storagebackend/config.go

@@ -17,6 +17,8 @@ limitations under the License.
 package storagebackend
 
 import (
+	"time"
+
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apiserver/pkg/storage/value"
 )
@@ -25,6 +27,8 @@ const (
 	StorageTypeUnset = ""
 	StorageTypeETCD2 = "etcd2"
 	StorageTypeETCD3 = "etcd3"
+
+	DefaultCompactInterval = 5 * time.Minute
 )
 
 // Config is configuration for creating a storage backend.
@@ -55,6 +59,10 @@ type Config struct {
 	Copier runtime.ObjectCopier
 	// Transformer allows the value to be transformed prior to persisting into etcd.
 	Transformer value.Transformer
+
+	// CompactionInterval is an interval of requesting compaction from apiserver.
+	// If the value is 0, no compaction will be issued.
+	CompactionInterval time.Duration
 }
 
 func NewDefaultConfig(prefix string, copier runtime.ObjectCopier, codec runtime.Codec) *Config {
@@ -63,7 +71,8 @@ func NewDefaultConfig(prefix string, copier runtime.ObjectCopier, codec runtime.
 		// Default cache size to 0 - if unset, its size will be set based on target
 		// memory usage.
 		DeserializationCacheSize: 0,
-		Copier: copier,
-		Codec:  codec,
+		Copier:             copier,
+		Codec:              codec,
+		CompactionInterval: DefaultCompactInterval,
 	}
 }

pkg/storage/storagebackend/factory/etcd3.go

@@ -51,7 +51,7 @@ func newETCD3Storage(c storagebackend.Config) (storage.Interface, DestroyFunc, e
 		return nil, nil, err
 	}
 	ctx, cancel := context.WithCancel(context.Background())
-	etcd3.StartCompactor(ctx, client)
+	etcd3.StartCompactor(ctx, client, c.CompactionInterval)
 	destroyFunc := func() {
 		cancel()
 		client.Close()