Add a config option specifying no snapshot restore on startup (#340)

api.go

@@ -291,19 +291,21 @@ func RecoverCluster(conf *Config, fsm FSM, logs LogStore, stable StableStore,
 		return fmt.Errorf("failed to list snapshots: %v", err)
 	}
 	for _, snapshot := range snapshots {
-		_, source, err := snaps.Open(snapshot.ID)
-		if err != nil {
-			// Skip this one and try the next. We will detect if we
-			// couldn't open any snapshots.
-			continue
-		}
+		if !conf.NoSnapshotRestoreOnStart {
+			_, source, err := snaps.Open(snapshot.ID)
+			if err != nil {
+				// Skip this one and try the next. We will detect if we
+				// couldn't open any snapshots.
+				continue
+			}
 
-		err = fsm.Restore(source)
-		// Close the source after the restore has completed
-		source.Close()
-		if err != nil {
-			// Same here, skip and try the next one.
-			continue
+			err = fsm.Restore(source)
+			// Close the source after the restore has completed
+			source.Close()
+			if err != nil {
+				// Same here, skip and try the next one.
+				continue
+			}
 		}
 
 		snapshotIndex = snapshot.Index
@@ -545,23 +547,23 @@ func (r *Raft) restoreSnapshot() error {
 
 	// Try to load in order of newest to oldest
 	for _, snapshot := range snapshots {
-		_, source, err := r.snapshots.Open(snapshot.ID)
-		if err != nil {
-			r.logger.Error(fmt.Sprintf("Failed to open snapshot %v: %v", snapshot.ID, err))
-			continue
-		}
-
-		err = r.fsm.Restore(source)
-		// Close the source after the restore has completed
-		source.Close()
-		if err != nil {
-			r.logger.Error(fmt.Sprintf("Failed to restore snapshot %v: %v", snapshot.ID, err))
-			continue
-		}
+		if !r.conf.NoSnapshotRestoreOnStart {
+			_, source, err := r.snapshots.Open(snapshot.ID)
+			if err != nil {
+				r.logger.Error(fmt.Sprintf("Failed to open snapshot %v: %v", snapshot.ID, err))
+				continue
+			}
 
-		// Log success
-		r.logger.Info(fmt.Sprintf("Restored from snapshot %v", snapshot.ID))
+			err = r.fsm.Restore(source)
+			// Close the source after the restore has completed
+			source.Close()
+			if err != nil {
+				r.logger.Error(fmt.Sprintf("Failed to restore snapshot %v: %v", snapshot.ID, err))
+				continue
+			}
 
+			r.logger.Info(fmt.Sprintf("Restored from snapshot %v", snapshot.ID))
+		}
 		// Update the lastApplied so we don't replay old logs
 		r.setLastApplied(snapshot.Index)
 

config.go

@@ -199,6 +199,13 @@ type Config struct {
 	// Logger is a user-provided hc-log logger. If nil, a logger writing to
 	// LogOutput with LogLevel is used.
 	Logger hclog.Logger
+
+	// NoSnapshotRestoreOnStart controls if raft will restore a snapshot to the
+	// FSM on start. This is useful if your FSM recovers from other mechanisms
+	// than raft snapshotting. Snapshot metadata will still be used to initalize
+	// raft's configuration and index values. This is used in NewRaft and
+	// RestoreCluster.
+	NoSnapshotRestoreOnStart bool
 }
 
 // DefaultConfig returns a Config with usable defaults.

raft_test.go

@@ -1671,6 +1671,48 @@ func TestRaft_SnapshotRestore(t *testing.T) {
 // TODO: Need a test to process old-style entries in the Raft log when starting
 // up.
 
+func TestRaft_NoRestoreOnStart(t *testing.T) {
+	conf := inmemConfig(t)
+	conf.TrailingLogs = 10
+	conf.NoSnapshotRestoreOnStart = true
+	c := MakeCluster(1, t, conf)
+
+	// Commit a lot of things.
+	leader := c.Leader()
+	var future Future
+	for i := 0; i < 100; i++ {
+		future = leader.Apply([]byte(fmt.Sprintf("test%d", i)), 0)
+	}
+
+	// Wait for the last future to apply
+	if err := future.Error(); err != nil {
+		c.FailNowf("[ERR] err: %v", err)
+	}
+
+	// Take a snapshot.
+	snapFuture := leader.Snapshot()
+	if err := snapFuture.Error(); err != nil {
+		c.FailNowf("[ERR] err: %v", err)
+	}
+
+	// Shutdown.
+	shutdown := leader.Shutdown()
+	if err := shutdown.Error(); err != nil {
+		c.FailNowf("[ERR] err: %v", err)
+	}
+
+	_, trans := NewInmemTransport(leader.localAddr)
+	newFSM := &MockFSM{}
+	_, err := NewRaft(&leader.conf, newFSM, leader.logs, leader.stable, leader.snapshots, trans)
+	if err != nil {
+		c.FailNowf("[ERR] err: %v", err)
+	}
+
+	if len(newFSM.logs) != 0 {
+		c.FailNowf("[ERR] expected empty FSM, got %v", newFSM)
+	}
+}
+
 func TestRaft_SnapshotRestore_PeerChange(t *testing.T) {
 	// Make the cluster.
 	conf := inmemConfig(t)