pd-ctl: print warn information when set max-replica to less than current

server/api/config.go

@@ -28,6 +28,7 @@ import (
 
 	"github.com/pingcap/errcode"
 	"github.com/pingcap/errors"
+	"github.com/pingcap/failpoint"
 	"github.com/pingcap/log"
 
 	"github.com/tikv/pd/pkg/errs"
@@ -411,6 +412,10 @@ func (h *confHandler) SetScheduleConfig(w http.ResponseWriter, r *http.Request)
 // @Success  200  {object}  sc.ReplicationConfig
 // @Router   /config/replicate [get]
 func (h *confHandler) GetReplicationConfig(w http.ResponseWriter, r *http.Request) {
+	failpoint.Inject("getReplicationConfigFailed", func(v failpoint.Value) {
+		code := v.(int)
+		h.rd.JSON(w, code, "get config failed")
+	})
 	if h.svr.IsServiceIndependent(constant.SchedulingServiceName) &&
 		r.Header.Get(apiutil.XForbiddenForwardToMicroserviceHeader) != "true" {
 		cfg, err := h.getSchedulingServerConfig()

tools/pd-ctl/pdctl/command/config_command.go

@@ -372,6 +372,8 @@ func postConfigDataWithPath(cmd *cobra.Command, key, value, path string) error {
 	val, err := strconv.ParseFloat(value, 64)
 	if err != nil {
 		val = value
+	} else if key == "max-replicas" {
+		checkMaxReplicas(cmd, val.(float64))
 	}
 	data[key] = val
 	reqData, err := json.Marshal(data)
@@ -386,6 +388,25 @@ func postConfigDataWithPath(cmd *cobra.Command, key, value, path string) error {
 	return nil
 }
 
+func checkMaxReplicas(cmd *cobra.Command, newReplica float64) {
+	header := buildHeader(cmd)
+	r, err := doRequest(cmd, replicatePrefix, http.MethodGet, header)
+	if err != nil {
+		cmd.Printf("Failed to get config when checking config: %s\n", err)
+		return
+	}
+	oldConfig := make(map[string]any)
+	err = json.Unmarshal([]byte(r), &oldConfig)
+	if err != nil {
+		cmd.Printf("Failed to unmarshal config when checking config: %s\n", err)
+		return
+	}
+	oldReplica, ok := oldConfig["max-replicas"].(float64)
+	if ok && newReplica < oldReplica {
+		cmd.Printf("Setting max-replica to %v which is less than the current replicas (%v). This may pose a risk. Please confirm the setting.\n", newReplica, oldReplica)
+	}
+}
+
 func setConfigCommandFunc(cmd *cobra.Command, args []string) {
 	if len(args) != 2 {
 		cmd.Println(cmd.UsageString())

tools/pd-ctl/tests/config/config_test.go

@@ -1199,6 +1199,51 @@ func (suite *configTestSuite) checkUpdateDefaultReplicaConfig(cluster *pdTests.T
 	checkRuleIsolationLevel("host")
 }
 
+func (suite *configTestSuite) TestMaxReplicaChanged() {
+	suite.env.RunTest(suite.checkMaxReplicaChanged)
+}
+
+func (suite *configTestSuite) checkMaxReplicaChanged(cluster *pdTests.TestCluster) {
+	re := suite.Require()
+	leaderServer := cluster.GetLeaderServer()
+	pdAddr := leaderServer.GetAddr()
+	cmd := ctl.GetRootCmd()
+
+	store := &metapb.Store{
+		Id:    1,
+		State: metapb.StoreState_Up,
+	}
+	pdTests.MustPutStore(re, cluster, store)
+
+	// test set max-replicas with invalid value
+	output, err := tests.ExecuteCommand(cmd, "-u", pdAddr, "config", "set", "max-replicas", "z")
+	re.NoError(err)
+	re.NotContains(string(output), "Success!")
+	// test set max-replicas with less value
+	output, err = tests.ExecuteCommand(cmd, "-u", pdAddr, "config", "set", "max-replicas", "2")
+	re.NoError(err)
+	re.Contains(string(output), "Success!")
+	re.Contains(string(output), "which is less than the current replicas")
+	// test set max-replicas with greater value
+	output, err = tests.ExecuteCommand(cmd, "-u", pdAddr, "config", "set", "max-replicas", "3")
+	re.NoError(err)
+	re.Contains(string(output), "Success!")
+	re.NotContains(string(output), "which is less than the current replicas")
+	// test meet error when get config failed
+	failpoint.Enable("github.com/tikv/pd/server/api/getReplicationConfigFailed", `return(200)`)
+	output, err = tests.ExecuteCommand(cmd, "-u", pdAddr, "config", "set", "max-replicas", "3")
+	re.NoError(err)
+	re.Contains(string(output), "Success!")
+	re.Contains(string(output), "Failed to unmarshal config when checking config")
+	failpoint.Disable("github.com/tikv/pd/server/api/getReplicationConfigFailed")
+	failpoint.Enable("github.com/tikv/pd/server/api/getReplicationConfigFailed", `return(500)`)
+	output, err = tests.ExecuteCommand(cmd, "-u", pdAddr, "config", "set", "max-replicas", "3")
+	re.NoError(err)
+	re.Contains(string(output), "Success!")
+	re.Contains(string(output), "Failed to get config when checking config")
+	failpoint.Disable("github.com/tikv/pd/server/api/getReplicationConfigFailed")
+}
+
 func (suite *configTestSuite) TestPDServerConfig() {
 	suite.env.RunTest(suite.checkPDServerConfig)
 }