fix(backup): dont allow to back up without possibility of restoring s…

…chema

Backups of clusters that restore from desc schema shouldn't be allowed
when the CQL creds are not set. This might break some backup tasks, but
it is better than silently skipping this step and founding out about it
during restore.

Fixes #3995

pkg/service/backup/worker_schema.go

@@ -35,36 +35,29 @@ func (w *worker) DumpSchema(ctx context.Context, hi []hostInfo, sessionFunc clus
 		return errors.Wrap(err, "get hosts supporting backup/restore from desc schema with internals")
 	}
 
-	var session gocqlx.Session
 	if len(descSchemaHosts) > 0 {
-		session, err = w.createSingleHostSessionToAnyHost(ctx, descSchemaHosts, sessionFunc)
-	} else {
-		session, err = sessionFunc(ctx, w.ClusterID)
+		return w.safeBackupAndRestoreSchemaDump(ctx, descSchemaHosts, sessionFunc)
 	}
+	w.unsafeBackupAndRestoreSchemaDump(ctx, sessionFunc)
+	return nil
+}
+
+func (w *worker) safeBackupAndRestoreSchemaDump(ctx context.Context, descSchemaHosts []string, sessionFunc cluster.SessionFunc) error {
+	w.Logger.Info(ctx, "Back up schema from DESCRIBE SCHEMA WITH INTERNALS")
+
+	session, err := w.createSingleHostSessionToAnyHost(ctx, descSchemaHosts, sessionFunc)
 	if err != nil {
 		if errors.Is(err, cluster.ErrNoCQLCredentials) {
-			w.Logger.Error(ctx, "No CQL cluster credentials, backup of schema as CQL files will be skipped", "error", err)
-			return nil
+			err = errors.Wrapf(err, "CQL credentials are required to back up schema for this ScyllaDB version")
 		}
-		return errors.Wrapf(err, "create cql session")
+		return errors.Wrap(err, "create single host CQL session")
 	}
 	defer session.Close()
 
-	if len(descSchemaHosts) > 0 {
-		return w.safeDumpSchema(ctx, session)
-	}
-	w.unsafeDumpSchema(ctx, session)
-	return nil
-}
-
-func (w *worker) safeDumpSchema(ctx context.Context, session gocqlx.Session) error {
-	w.Logger.Info(ctx, "Schema backup for used ScyllaDB version is done via DESCRIBE SCHEMA WITH INTERNALS CQL query. "+
-		"ScyllaDB Manager will snapshot system_schema sstables, but they won't be used during schema restoration")
 	if err := query.RaftReadBarrier(session); err != nil {
-		w.Logger.Error(ctx, "Couldn't perform raft read barrier, backup of schema as CQL files will be skipped "+
-			"(restoring schema from this backup won't be possible)", "error", err)
-		return nil
+		return errors.Wrap(err, "perform raft read barrier on desc schema host")
 	}
+
 	schema, err := query.DescribeSchemaWithInternals(session)
 	if err != nil {
 		return err
@@ -73,23 +66,33 @@ func (w *worker) safeDumpSchema(ctx context.Context, session gocqlx.Session) err
 	if err != nil {
 		return errors.Wrap(err, "create safe schema file")
 	}
+
 	w.SchemaFilePath = backupspec.RemoteSchemaFile(w.ClusterID, w.TaskID, w.SnapshotTag)
 	w.Schema = b
 	return nil
 }
 
-func (w *worker) unsafeDumpSchema(ctx context.Context, session gocqlx.Session) {
-	w.Logger.Info(ctx, "Schema backup for used ScyllaDB version is done via snapshot of system_schema sstables. "+
-		"ScyllaDB Manager will try to create unsafe schema CQL archive, but it won't be used during schema restoration")
+func (w *worker) unsafeBackupAndRestoreSchemaDump(ctx context.Context, sessionFunc cluster.SessionFunc) {
+	w.Logger.Info(ctx, "Back up schema from sstables")
+	const explanation = ", backup of schema as CQL files will be skipped (for this ScyllaDB version schema is restored directly from sstables)"
+
+	session, err := sessionFunc(ctx, w.ClusterID)
+	if err != nil {
+		w.Logger.Error(ctx, "Couldn't create CQL session"+explanation, "error", err)
+		return
+	}
+	defer session.Close()
+
 	if err := session.AwaitSchemaAgreement(ctx); err != nil {
-		w.Logger.Error(ctx, "Couldn't await schema agreement, backup of unsafe schema as CQL files will be skipped", "error", err)
+		w.Logger.Error(ctx, "Couldn't await schema agreement"+explanation, "error", err)
 		return
 	}
 	b, err := createUnsafeSchemaArchive(ctx, w.Units, session)
 	if err != nil {
-		w.Logger.Error(ctx, "Couldn't create unsafe schema archive, backup of unsafe schema as CQL files will be skipped", "error", err)
+		w.Logger.Error(ctx, "Couldn't create schema archive"+explanation, "error", err)
 		return
 	}
+
 	w.SchemaFilePath = backupspec.RemoteUnsafeSchemaFile(w.ClusterID, w.TaskID, w.SnapshotTag)
 	w.Schema = b
 }