print error log when validation on conf change failed

Signed-off-by: Benjamin Wang <[email protected]>

server/etcdserver/server.go

@@ -2351,7 +2351,9 @@ func (s *EtcdServer) notifyAboutFirstCommitInTerm() {
 // applyConfChange applies a ConfChange to the server. It is only
 // invoked with a ConfChange that has already passed through Raft
 func (s *EtcdServer) applyConfChange(cc raftpb.ConfChange, confState *raftpb.ConfState, shouldApplyV3 membership.ShouldApplyV3) (bool, error) {
+	lg := s.Logger()
 	if err := s.cluster.ValidateConfigurationChange(cc); err != nil {
+		lg.Error("Validation on configuration change failed", zap.Bool("shouldApplyV3", bool(shouldApplyV3)), zap.Error(err))
 		cc.NodeID = raft.None
 		s.r.ApplyConfChange(cc)
 
@@ -2364,7 +2366,6 @@ func (s *EtcdServer) applyConfChange(cc raftpb.ConfChange, confState *raftpb.Con
 		return false, err
 	}
 
-	lg := s.Logger()
 	*confState = *s.r.ApplyConfChange(cc)
 	s.beHooks.SetConfState(confState)
 	switch cc.Type {