storage, etcd3: add an option for turning on/off compaction from apis…

…erver

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.DisableCompaction`. If the flag is false (default),
apiserver issues the compaction requests like current behaviour. If it
is true, apiserver doesn't issue the requests. It can be configured
with a newly added option of apiserver `--etcd-disable-compaction`.

staging/src/k8s.io/apiserver/pkg/server/options/etcd.go

@@ -127,6 +127,10 @@ 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.BoolVar(&s.StorageConfig.DisableCompaction, "etcd-disable-compaction", s.StorageConfig.DisableCompaction,
+		"If true, disable issuing compaction request from apiserver.")
+
 }
 
 func (s *EtcdOptions) ApplyTo(c *server.Config) error {

staging/src/k8s.io/apiserver/pkg/storage/storagebackend/config.go

@@ -50,6 +50,9 @@ type Config struct {
 	Copier runtime.ObjectCopier
 	// Transformer allows the value to be transformed prior to persisting into etcd.
 	Transformer value.Transformer
+
+	// DisableCompaction is a flag to turn off requesting compaction from apiserver.
+	DisableCompaction bool
 }
 
 func NewDefaultConfig(prefix string, copier runtime.ObjectCopier, codec runtime.Codec) *Config {
@@ -58,7 +61,8 @@ 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,
+		DisableCompaction: false,
 	}
 }

staging/src/k8s.io/apiserver/pkg/storage/storagebackend/factory/etcd3.go

@@ -51,7 +51,9 @@ func newETCD3Storage(c storagebackend.Config) (storage.Interface, DestroyFunc, e
 		return nil, nil, err
 	}
 	ctx, cancel := context.WithCancel(context.Background())
-	etcd3.StartCompactor(ctx, client)
+	if !c.DisableCompaction {
+		etcd3.StartCompactor(ctx, client)
+	}
 	destroyFunc := func() {
 		cancel()
 		client.Close()