site replication: fix healing of bucket deletes. (#15377)

This PR changes the handling of bucket deletes for site 
replicated setups to hold on to deleted bucket state until 
it syncs to all the clusters participating in site replication.

cmd/bucket-metadata.go

@@ -105,10 +105,8 @@ type BucketMetadata struct {
 
 // newBucketMetadata creates BucketMetadata with the supplied name and Created to Now.
 func newBucketMetadata(name string) BucketMetadata {
-	now := UTCNow()
 	return BucketMetadata{
-		Name:    name,
-		Created: now,
+		Name: name,
 		notificationConfig: &event.Config{
 			XMLNS: "http://s3.amazonaws.com/doc/2006-03-01/",
 		},
@@ -121,6 +119,17 @@ func newBucketMetadata(name string) BucketMetadata {
 	}
 }
 
+// SetCreatedAt preserves the CreatedAt time for bucket across sites in site replication. It defaults to
+// creation time of bucket on this cluster in all other cases.
+func (b *BucketMetadata) SetCreatedAt(createdAt time.Time) {
+	if b.Created.IsZero() {
+		b.Created = UTCNow()
+	}
+	if !createdAt.IsZero() {
+		b.Created = createdAt.UTC()
+	}
+}
+
 // Load - loads the metadata of bucket by name from ObjectLayer api.
 // If an error is returned the returned metadata will be default initialized.
 func (b *BucketMetadata) Load(ctx context.Context, api ObjectLayer, name string) error {
@@ -160,17 +169,19 @@ func loadBucketMetadata(ctx context.Context, objectAPI ObjectLayer, bucket strin
 	if err != nil && !errors.Is(err, errConfigNotFound) {
 		return b, err
 	}
-
+	if err == nil {
+		b.defaultTimestamps()
+	}
 	// Old bucket without bucket metadata. Hence we migrate existing settings.
 	if err := b.convertLegacyConfigs(ctx, objectAPI); err != nil {
 		return b, err
 	}
 
 	// migrate unencrypted remote targets
-	if err = b.migrateTargetConfig(ctx, objectAPI); err != nil {
+	if err := b.migrateTargetConfig(ctx, objectAPI); err != nil {
 		return b, err
 	}
-	b.defaultTimestamps()
+
 	return b, nil
 }
 
@@ -345,6 +356,7 @@ func (b *BucketMetadata) convertLegacyConfigs(ctx context.Context, objectAPI Obj
 			b.BucketTargetsConfigJSON = configData
 		}
 	}
+	b.defaultTimestamps()
 
 	if err := b.Save(ctx, objectAPI); err != nil {
 		return err