Merge pull request #10725 from jingyih/learner_part1

*: support raft learner in etcd - part 1

Documentation/dev-guide/api_reference_v3.md

@@ -37,6 +37,7 @@ This is a generated documentation. Please read the proto files for more.
 | MemberRemove | MemberRemoveRequest | MemberRemoveResponse | MemberRemove removes an existing member from the cluster. |
 | MemberUpdate | MemberUpdateRequest | MemberUpdateResponse | MemberUpdate updates the member configuration. |
 | MemberList | MemberListRequest | MemberListResponse | MemberList lists all the members in the cluster. |
+| MemberPromote | MemberPromoteRequest | MemberPromoteResponse | MemberPromote promotes a member from raft learner (non-voting) to raft voting member. |
 
 
 
@@ -609,6 +610,7 @@ Empty field.
 | name | name is the human-readable name of the member. If the member is not started, the name will be an empty string. | string |
 | peerURLs | peerURLs is the list of URLs the member exposes to the cluster for communication. | (slice of) string |
 | clientURLs | clientURLs is the list of URLs the member exposes to clients for communication. If the member is not started, clientURLs will be empty. | (slice of) string |
+| isLearner | isLearner indicates if the member is raft learner. | bool |
 
 
 
@@ -617,6 +619,7 @@ Empty field.
 | Field | Description | Type |
 | ----- | ----------- | ---- |
 | peerURLs | peerURLs is the list of URLs the added member will use to communicate with the cluster. | (slice of) string |
+| isLearner | isLearner indicates if the added member is raft learner. | bool |
 
 
 
@@ -645,6 +648,23 @@ Empty field.
 
 
 
+##### message `MemberPromoteRequest` (etcdserver/etcdserverpb/rpc.proto)
+
+| Field | Description | Type |
+| ----- | ----------- | ---- |
+| ID | ID is the member ID of the member to promote. | uint64 |
+
+
+
+##### message `MemberPromoteResponse` (etcdserver/etcdserverpb/rpc.proto)
+
+| Field | Description | Type |
+| ----- | ----------- | ---- |
+| header |  | ResponseHeader |
+| members | members is a list of all members after promoting the member. | (slice of) Member |
+
+
+
 ##### message `MemberRemoveRequest` (etcdserver/etcdserverpb/rpc.proto)
 
 | Field | Description | Type |
@@ -819,6 +839,7 @@ Empty field.
 | raftAppliedIndex | raftAppliedIndex is the current raft applied index of the responding member. | uint64 |
 | errors | errors contains alarm/health information and status. | (slice of) string |
 | dbSizeInUse | dbSizeInUse is the size of the backend database logically in use, in bytes, of the responding member. | int64 |
+| isLearner | isLearner indicates if the member is raft learner. | bool |
 
 
 

Documentation/dev-guide/apispec/swagger/rpc.swagger.json

@@ -501,6 +501,33 @@
         }
       }
     },
+    "/v3/cluster/member/promote": {
+      "post": {
+        "tags": [
+          "Cluster"
+        ],
+        "summary": "MemberPromote promotes a member from raft learner (non-voting) to raft voting member.",
+        "operationId": "MemberPromote",
+        "parameters": [
+          {
+            "name": "body",
+            "in": "body",
+            "required": true,
+            "schema": {
+              "$ref": "#/definitions/etcdserverpbMemberPromoteRequest"
+            }
+          }
+        ],
+        "responses": {
+          "200": {
+            "description": "A successful response.",
+            "schema": {
+              "$ref": "#/definitions/etcdserverpbMemberPromoteResponse"
+            }
+          }
+        }
+      }
+    },
     "/v3/cluster/member/remove": {
       "post": {
         "tags": [
@@ -820,7 +847,7 @@
           "200": {
             "description": "A successful response.(streaming responses)",
             "schema": {
-              "$ref": "#/definitions/etcdserverpbLeaseKeepAliveResponse"
+              "$ref": "#/x-stream-definitions/etcdserverpbLeaseKeepAliveResponse"
             }
           }
         }
@@ -1009,7 +1036,7 @@
           "200": {
             "description": "A successful response.(streaming responses)",
             "schema": {
-              "$ref": "#/definitions/etcdserverpbSnapshotResponse"
+              "$ref": "#/x-stream-definitions/etcdserverpbSnapshotResponse"
             }
           }
         }
@@ -1091,7 +1118,7 @@
           "200": {
             "description": "A successful response.(streaming responses)",
             "schema": {
-              "$ref": "#/definitions/etcdserverpbWatchResponse"
+              "$ref": "#/x-stream-definitions/etcdserverpbWatchResponse"
             }
           }
         }
@@ -1882,6 +1909,11 @@
             "type": "string"
           }
         },
+        "isLearner": {
+          "description": "isLearner indicates if the member is raft learner.",
+          "type": "boolean",
+          "format": "boolean"
+        },
         "name": {
           "description": "name is the human-readable name of the member. If the member is not started, the name will be an empty string.",
           "type": "string"
@@ -1898,6 +1930,11 @@
     "etcdserverpbMemberAddRequest": {
       "type": "object",
       "properties": {
+        "isLearner": {
+          "description": "isLearner indicates if the added member is raft learner.",
+          "type": "boolean",
+          "format": "boolean"
+        },
         "peerURLs": {
           "description": "peerURLs is the list of URLs the added member will use to communicate with the cluster.",
           "type": "array",
@@ -1944,6 +1981,31 @@
         }
       }
     },
+    "etcdserverpbMemberPromoteRequest": {
+      "type": "object",
+      "properties": {
+        "ID": {
+          "description": "ID is the member ID of the member to promote.",
+          "type": "string",
+          "format": "uint64"
+        }
+      }
+    },
+    "etcdserverpbMemberPromoteResponse": {
+      "type": "object",
+      "properties": {
+        "header": {
+          "$ref": "#/definitions/etcdserverpbResponseHeader"
+        },
+        "members": {
+          "description": "members is a list of all members after promoting the member.",
+          "type": "array",
+          "items": {
+            "$ref": "#/definitions/etcdserverpbMember"
+          }
+        }
+      }
+    },
     "etcdserverpbMemberRemoveRequest": {
       "type": "object",
       "properties": {
@@ -2266,6 +2328,11 @@
         "header": {
           "$ref": "#/definitions/etcdserverpbResponseHeader"
         },
+        "isLearner": {
+          "description": "isLearner indicates if the member is raft learner.",
+          "type": "boolean",
+          "format": "boolean"
+        },
         "leader": {
           "description": "leader is the member ID which the responding member believes is the current leader.",
           "type": "string",
@@ -2508,6 +2575,43 @@
           "format": "int64"
         }
       }
+    },
+    "protobufAny": {
+      "type": "object",
+      "properties": {
+        "type_url": {
+          "type": "string"
+        },
+        "value": {
+          "type": "string",
+          "format": "byte"
+        }
+      }
+    },
+    "runtimeStreamError": {
+      "type": "object",
+      "properties": {
+        "details": {
+          "type": "array",
+          "items": {
+            "$ref": "#/definitions/protobufAny"
+          }
+        },
+        "grpc_code": {
+          "type": "integer",
+          "format": "int32"
+        },
+        "http_code": {
+          "type": "integer",
+          "format": "int32"
+        },
+        "http_status": {
+          "type": "string"
+        },
+        "message": {
+          "type": "string"
+        }
+      }
     }
   },
   "securityDefinitions": {
@@ -2521,5 +2625,43 @@
     {
       "ApiKey": []
     }
-  ]
+  ],
+  "x-stream-definitions": {
+    "etcdserverpbLeaseKeepAliveResponse": {
+      "properties": {
+        "error": {
+          "$ref": "#/definitions/runtimeStreamError"
+        },
+        "result": {
+          "$ref": "#/definitions/etcdserverpbLeaseKeepAliveResponse"
+        }
+      },
+      "title": "Stream result of etcdserverpbLeaseKeepAliveResponse",
+      "type": "object"
+    },
+    "etcdserverpbSnapshotResponse": {
+      "properties": {
+        "error": {
+          "$ref": "#/definitions/runtimeStreamError"
+        },
+        "result": {
+          "$ref": "#/definitions/etcdserverpbSnapshotResponse"
+        }
+      },
+      "title": "Stream result of etcdserverpbSnapshotResponse",
+      "type": "object"
+    },
+    "etcdserverpbWatchResponse": {
+      "properties": {
+        "error": {
+          "$ref": "#/definitions/runtimeStreamError"
+        },
+        "result": {
+          "$ref": "#/definitions/etcdserverpbWatchResponse"
+        }
+      },
+      "title": "Stream result of etcdserverpbWatchResponse",
+      "type": "object"
+    }
+  }
 }

Documentation/dev-guide/apispec/swagger/v3election.swagger.json

@@ -77,7 +77,7 @@
           "200": {
             "description": "A successful response.(streaming responses)",
             "schema": {
-              "$ref": "#/definitions/v3electionpbLeaderResponse"
+              "$ref": "#/x-stream-definitions/v3electionpbLeaderResponse"
             }
           }
         },
@@ -212,6 +212,43 @@
         }
       }
     },
+    "protobufAny": {
+      "type": "object",
+      "properties": {
+        "type_url": {
+          "type": "string"
+        },
+        "value": {
+          "type": "string",
+          "format": "byte"
+        }
+      }
+    },
+    "runtimeStreamError": {
+      "type": "object",
+      "properties": {
+        "grpc_code": {
+          "type": "integer",
+          "format": "int32"
+        },
+        "http_code": {
+          "type": "integer",
+          "format": "int32"
+        },
+        "message": {
+          "type": "string"
+        },
+        "http_status": {
+          "type": "string"
+        },
+        "details": {
+          "type": "array",
+          "items": {
+            "$ref": "#/definitions/protobufAny"
+          }
+        }
+      }
+    },
     "v3electionpbCampaignRequest": {
       "type": "object",
       "properties": {
@@ -330,5 +367,19 @@
         }
       }
     }
+  },
+  "x-stream-definitions": {
+    "v3electionpbLeaderResponse": {
+      "type": "object",
+      "properties": {
+        "result": {
+          "$ref": "#/definitions/v3electionpbLeaderResponse"
+        },
+        "error": {
+          "$ref": "#/definitions/runtimeStreamError"
+        }
+      },
+      "title": "Stream result of v3electionpbLeaderResponse"
+    }
   }
 }

clientv3/cluster.go

@@ -16,6 +16,7 @@ package clientv3
 
 import (
 	"context"
+	"errors"
 
 	pb "go.etcd.io/etcd/v3/etcdserver/etcdserverpb"
 	"go.etcd.io/etcd/v3/pkg/types"
@@ -29,6 +30,7 @@ type (
 	MemberAddResponse     pb.MemberAddResponse
 	MemberRemoveResponse  pb.MemberRemoveResponse
 	MemberUpdateResponse  pb.MemberUpdateResponse
+	MemberPromoteResponse pb.MemberPromoteResponse
 )
 
 type Cluster interface {
@@ -38,11 +40,17 @@ type Cluster interface {
 	// MemberAdd adds a new member into the cluster.
 	MemberAdd(ctx context.Context, peerAddrs []string) (*MemberAddResponse, error)
 
+	// MemberAddAsLearner adds a new learner member into the cluster.
+	MemberAddAsLearner(ctx context.Context, peerAddrs []string) (*MemberAddResponse, error)
+
 	// MemberRemove removes an existing member from the cluster.
 	MemberRemove(ctx context.Context, id uint64) (*MemberRemoveResponse, error)
 
 	// MemberUpdate updates the peer addresses of the member.
 	MemberUpdate(ctx context.Context, id uint64, peerAddrs []string) (*MemberUpdateResponse, error)
+
+	// MemberPromote promotes a member from raft learner (non-voting) to raft voting member.
+	MemberPromote(ctx context.Context, id uint64) (*MemberPromoteResponse, error)
 }
 
 type cluster struct {
@@ -67,12 +75,23 @@ func NewClusterFromClusterClient(remote pb.ClusterClient, c *Client) Cluster {
 }
 
 func (c *cluster) MemberAdd(ctx context.Context, peerAddrs []string) (*MemberAddResponse, error) {
+	return c.memberAdd(ctx, peerAddrs, false)
+}
+
+func (c *cluster) MemberAddAsLearner(ctx context.Context, peerAddrs []string) (*MemberAddResponse, error) {
+	return c.memberAdd(ctx, peerAddrs, true)
+}
+
+func (c *cluster) memberAdd(ctx context.Context, peerAddrs []string, isLearner bool) (*MemberAddResponse, error) {
 	// fail-fast before panic in rafthttp
 	if _, err := types.NewURLs(peerAddrs); err != nil {
 		return nil, err
 	}
 
-	r := &pb.MemberAddRequest{PeerURLs: peerAddrs}
+	r := &pb.MemberAddRequest{
+		PeerURLs:  peerAddrs,
+		IsLearner: isLearner,
+	}
 	resp, err := c.remote.MemberAdd(ctx, r, c.callOpts...)
 	if err != nil {
 		return nil, toErr(ctx, err)
@@ -112,3 +131,8 @@ func (c *cluster) MemberList(ctx context.Context) (*MemberListResponse, error) {
 	}
 	return nil, toErr(ctx, err)
 }
+
+func (c *cluster) MemberPromote(ctx context.Context, id uint64) (*MemberPromoteResponse, error) {
+	// TODO: implement
+	return nil, errors.New("not implemented")
+}

clientv3/example_cluster_test.go

@@ -59,6 +59,27 @@ func ExampleCluster_memberAdd() {
 	// added member.PeerURLs: [http://localhost:32380]
 }
 
+func ExampleCluster_memberAddAsLearner() {
+	cli, err := clientv3.New(clientv3.Config{
+		Endpoints:   endpoints[:2],
+		DialTimeout: dialTimeout,
+	})
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer cli.Close()
+
+	peerURLs := endpoints[2:]
+	mresp, err := cli.MemberAddAsLearner(context.Background(), peerURLs)
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Println("added member.PeerURLs:", mresp.Member.PeerURLs)
+	fmt.Println("added member.IsLearner:", mresp.Member.IsLearner)
+	// added member.PeerURLs: [http://localhost:32380]
+	// added member.IsLearner: true
+}
+
 func ExampleCluster_memberRemove() {
 	cli, err := clientv3.New(clientv3.Config{
 		Endpoints:   endpoints[1:],

clientv3/integration/cluster_test.go

@@ -16,6 +16,7 @@ package integration
 
 import (
 	"context"
+	"fmt"
 	"reflect"
 	"strings"
 	"testing"
@@ -184,3 +185,46 @@ func TestMemberAddUpdateWrongURLs(t *testing.T) {
 		}
 	}
 }
+
+func TestMemberAddForLearner(t *testing.T) {
+	defer testutil.AfterTest(t)
+
+	clus := integration.NewClusterV3(t, &integration.ClusterConfig{Size: 3})
+	defer clus.Terminate(t)
+
+	capi := clus.RandClient()
+
+	urls := []string{"http://127.0.0.1:1234"}
+	resp, err := capi.MemberAddAsLearner(context.Background(), urls)
+	if err != nil {
+		t.Fatalf("failed to add member %v", err)
+	}
+
+	if !resp.Member.IsLearner {
+		t.Errorf("Added a member as learner, got resp.Member.IsLearner = %v", resp.Member.IsLearner)
+	}
+
+	numOfLearners, err := getNumberOfLearners(clus)
+	if err != nil {
+		t.Fatalf("failed to get the number of learners in cluster: %v", err)
+	}
+	if numOfLearners != 1 {
+		t.Errorf("Added 1 learner node to cluster, got %d", numOfLearners)
+	}
+}
+
+// getNumberOfLearners return the number of learner nodes in cluster using MemberList API
+func getNumberOfLearners(clus *integration.ClusterV3) (int, error) {
+	cli := clus.RandClient()
+	resp, err := cli.MemberList(context.Background())
+	if err != nil {
+		return 0, fmt.Errorf("failed to list member %v", err)
+	}
+	numberOfLearners := 0
+	for _, m := range resp.Members {
+		if m.IsLearner {
+			numberOfLearners++
+		}
+	}
+	return numberOfLearners, nil
+}

clientv3/retry.go

@@ -183,6 +183,10 @@ func (rcc *retryClusterClient) MemberUpdate(ctx context.Context, in *pb.MemberUp
 	return rcc.cc.MemberUpdate(ctx, in, opts...)
 }
 
+func (rcc *retryClusterClient) MemberPromote(ctx context.Context, in *pb.MemberPromoteRequest, opts ...grpc.CallOption) (resp *pb.MemberPromoteResponse, err error) {
+	return rcc.cc.MemberPromote(ctx, in, opts...)
+}
+
 type retryMaintenanceClient struct {
 	mc pb.MaintenanceClient
 }

etcdctl/ctlv3/command/member_command.go

@@ -21,9 +21,13 @@ import (
 	"strings"
 
 	"github.com/spf13/cobra"
+	"go.etcd.io/etcd/v3/clientv3"
 )
 
-var memberPeerURLs string
+var (
+	memberPeerURLs string
+	isLearner      bool
+)
 
 // NewMemberCommand returns the cobra command for "member".
 func NewMemberCommand() *cobra.Command {
@@ -50,6 +54,7 @@ func NewMemberAddCommand() *cobra.Command {
 	}
 
 	cc.Flags().StringVar(&memberPeerURLs, "peer-urls", "", "comma separated peer URLs for the new member.")
+	cc.Flags().BoolVar(&isLearner, "learner", false, "indicates if the new member is raft learner")
 
 	return cc
 }
@@ -86,7 +91,7 @@ func NewMemberListCommand() *cobra.Command {
 		Use:   "list",
 		Short: "Lists all members in the cluster",
 		Long: `When --write-out is set to simple, this command prints out comma-separated member lists for each endpoint.
-The items in the lists are ID, Status, Name, Peer Addrs, Client Addrs.
+The items in the lists are ID, Status, Name, Peer Addrs, Client Addrs, Is Learner.
 `,
 
 		Run: memberListCommandFunc,
@@ -118,7 +123,15 @@ func memberAddCommandFunc(cmd *cobra.Command, args []string) {
 	urls := strings.Split(memberPeerURLs, ",")
 	ctx, cancel := commandCtx(cmd)
 	cli := mustClientFromCmd(cmd)
-	resp, err := cli.MemberAdd(ctx, urls)
+	var (
+		resp *clientv3.MemberAddResponse
+		err  error
+	)
+	if isLearner {
+		resp, err = cli.MemberAddAsLearner(ctx, urls)
+	} else {
+		resp, err = cli.MemberAdd(ctx, urls)
+	}
 	cancel()
 	if err != nil {
 		ExitWithError(ExitError, err)

etcdctl/ctlv3/command/printer.go

@@ -158,18 +158,23 @@ func (p *printerUnsupported) DBStatus(snapshot.Status)  { p.p(nil) }
 func (p *printerUnsupported) MoveLeader(leader, target uint64, r v3.MoveLeaderResponse) { p.p(nil) }
 
 func makeMemberListTable(r v3.MemberListResponse) (hdr []string, rows [][]string) {
-	hdr = []string{"ID", "Status", "Name", "Peer Addrs", "Client Addrs"}
+	hdr = []string{"ID", "Status", "Name", "Peer Addrs", "Client Addrs", "Is Learner"}
 	for _, m := range r.Members {
 		status := "started"
 		if len(m.Name) == 0 {
 			status = "unstarted"
 		}
+		isLearner := "false"
+		if m.IsLearner {
+			isLearner = "true"
+		}
 		rows = append(rows, []string{
 			fmt.Sprintf("%x", m.ID),
 			status,
 			m.Name,
 			strings.Join(m.PeerURLs, ","),
 			strings.Join(m.ClientURLs, ","),
+			isLearner,
 		})
 	}
 	return hdr, rows

etcdctl/ctlv3/command/printer_fields.go

@@ -137,6 +137,7 @@ func (p *fieldsPrinter) MemberList(r v3.MemberListResponse) {
 		for _, u := range m.ClientURLs {
 			fmt.Printf("\"ClientURL\" : %q\n", u)
 		}
+		fmt.Println(`"IsLearner" :`, m.IsLearner)
 		fmt.Println()
 	}
 }

etcdserver/api/membership/cluster.go

@@ -59,6 +59,8 @@ type RaftCluster struct {
 	removed map[types.ID]bool
 }
 
+// NewClusterFromURLsMap creates a new raft cluster using provided urls map. Currently, it does not support creating
+// cluster with raft learner member.
 func NewClusterFromURLsMap(lg *zap.Logger, token string, urlsmap types.URLsMap) (*RaftCluster, error) {
 	c := NewCluster(lg, token)
 	for name, urls := range urlsmap {
@@ -259,7 +261,7 @@ func (c *RaftCluster) ValidateConfigurationChange(cc raftpb.ConfChange) error {
 		return ErrIDRemoved
 	}
 	switch cc.Type {
-	case raftpb.ConfChangeAddNode:
+	case raftpb.ConfChangeAddNode, raftpb.ConfChangeAddLearnerNode:
 		if members[id] != nil {
 			return ErrIDExists
 		}

etcdserver/api/membership/cluster_test.go

@@ -472,6 +472,29 @@ func TestClusterAddMember(t *testing.T) {
 	}
 }
 
+func TestClusterAddMemberAsLearner(t *testing.T) {
+	st := mockstore.NewRecorder()
+	c := newTestCluster(nil)
+	c.SetStore(st)
+	c.AddMember(newTestMemberAsLearner(1, nil, "node1", nil))
+
+	wactions := []testutil.Action{
+		{
+			Name: "Create",
+			Params: []interface{}{
+				path.Join(StoreMembersPrefix, "1", "raftAttributes"),
+				false,
+				`{"peerURLs":null,"isLearner":true}`,
+				false,
+				v2store.TTLOptionSet{ExpireTime: v2store.Permanent},
+			},
+		},
+	}
+	if g := st.Action(); !reflect.DeepEqual(g, wactions) {
+		t.Errorf("actions = %v, want %v", g, wactions)
+	}
+}
+
 func TestClusterMembers(t *testing.T) {
 	cls := &RaftCluster{
 		members: map[types.ID]*Member{

etcdserver/api/membership/member.go

@@ -35,6 +35,8 @@ type RaftAttributes struct {
 	// PeerURLs is the list of peers in the raft cluster.
 	// TODO(philips): ensure these are URLs
 	PeerURLs []string `json:"peerURLs"`
+	// IsLearner indicates if the member is raft learner.
+	IsLearner bool `json:"isLearner,omitempty"`
 }
 
 // Attributes represents all the non-raft related attributes of an etcd member.
@@ -52,8 +54,21 @@ type Member struct {
 // NewMember creates a Member without an ID and generates one based on the
 // cluster name, peer URLs, and time. This is used for bootstrapping/adding new member.
 func NewMember(name string, peerURLs types.URLs, clusterName string, now *time.Time) *Member {
+	return newMember(name, peerURLs, clusterName, now, false)
+}
+
+// NewMemberAsLearner creates a learner Member without an ID and generates one based on the
+// cluster name, peer URLs, and time. This is used for adding new learner member.
+func NewMemberAsLearner(name string, peerURLs types.URLs, clusterName string, now *time.Time) *Member {
+	return newMember(name, peerURLs, clusterName, now, true)
+}
+
+func newMember(name string, peerURLs types.URLs, clusterName string, now *time.Time, isLearner bool) *Member {
 	m := &Member{
-		RaftAttributes: RaftAttributes{PeerURLs: peerURLs.StringSlice()},
+		RaftAttributes: RaftAttributes{
+			PeerURLs:  peerURLs.StringSlice(),
+			IsLearner: isLearner,
+		},
 		Attributes: Attributes{Name: name},
 	}
 
@@ -88,6 +103,9 @@ func (m *Member) Clone() *Member {
 	}
 	mm := &Member{
 		ID: m.ID,
+		RaftAttributes: RaftAttributes{
+			IsLearner: m.IsLearner,
+		},
 		Attributes: Attributes{
 			Name: m.Name,
 		},

etcdserver/api/membership/member_test.go

@@ -113,3 +113,11 @@ func newTestMember(id uint64, peerURLs []string, name string, clientURLs []strin
 		Attributes:     Attributes{Name: name, ClientURLs: clientURLs},
 	}
 }
+
+func newTestMemberAsLearner(id uint64, peerURLs []string, name string, clientURLs []string) *Member {
+	return &Member{
+		ID:             types.ID(id),
+		RaftAttributes: RaftAttributes{PeerURLs: peerURLs, IsLearner: true},
+		Attributes:     Attributes{Name: name, ClientURLs: clientURLs},
+	}
+}

etcdserver/api/v2v3/server.go

@@ -63,6 +63,7 @@ func (s *v2v3Server) Leader() types.ID {
 }
 
 func (s *v2v3Server) AddMember(ctx context.Context, memb membership.Member) ([]*membership.Member, error) {
+	// adding member as learner is not supported by V2 Server.
 	resp, err := s.c.MemberAdd(ctx, memb.PeerURLs)
 	if err != nil {
 		return nil, err
@@ -93,6 +94,7 @@ func v3MembersToMembership(v3membs []*pb.Member) []*membership.Member {
 			ID: types.ID(m.ID),
 			RaftAttributes: membership.RaftAttributes{
 				PeerURLs:  m.PeerURLs,
+				IsLearner: m.IsLearner,
 			},
 			Attributes: membership.Attributes{
 				Name:       m.Name,

etcdserver/api/v3rpc/member.go

@@ -16,6 +16,7 @@ package v3rpc
 
 import (
 	"context"
+	"errors"
 	"time"
 
 	"go.etcd.io/etcd/v3/etcdserver"
@@ -45,7 +46,12 @@ func (cs *ClusterServer) MemberAdd(ctx context.Context, r *pb.MemberAddRequest)
 	}
 
 	now := time.Now()
-	m := membership.NewMember("", urls, "", &now)
+	var m *membership.Member
+	if r.IsLearner {
+		m = membership.NewMemberAsLearner("", urls, "", &now)
+	} else {
+		m = membership.NewMember("", urls, "", &now)
+	}
 	membs, merr := cs.server.AddMember(ctx, *m)
 	if merr != nil {
 		return nil, togRPCError(merr)
@@ -53,7 +59,11 @@ func (cs *ClusterServer) MemberAdd(ctx context.Context, r *pb.MemberAddRequest)
 
 	return &pb.MemberAddResponse{
 		Header: cs.header(),
-		Member:  &pb.Member{ID: uint64(m.ID), PeerURLs: m.PeerURLs},
+		Member: &pb.Member{
+			ID:        uint64(m.ID),
+			PeerURLs:  m.PeerURLs,
+			IsLearner: m.IsLearner,
+		},
 		Members: membersToProtoMembers(membs),
 	}, nil
 }
@@ -83,6 +93,11 @@ func (cs *ClusterServer) MemberList(ctx context.Context, r *pb.MemberListRequest
 	return &pb.MemberListResponse{Header: cs.header(), Members: membs}, nil
 }
 
+func (cs *ClusterServer) MemberPromote(ctx context.Context, r *pb.MemberPromoteRequest) (*pb.MemberPromoteResponse, error) {
+	// TODO: implement
+	return nil, errors.New("not implemented")
+}
+
 func (cs *ClusterServer) header() *pb.ResponseHeader {
 	return &pb.ResponseHeader{ClusterId: uint64(cs.cluster.ID()), MemberId: uint64(cs.server.ID()), RaftTerm: cs.server.Term()}
 }
@@ -95,6 +110,7 @@ func membersToProtoMembers(membs []*membership.Member) []*pb.Member {
 			ID:         uint64(membs[i].ID),
 			PeerURLs:   membs[i].PeerURLs,
 			ClientURLs: membs[i].ClientURLs,
+			IsLearner:  membs[i].IsLearner,
 		}
 	}
 	return protoMembs

etcdserver/etcdserverpb/etcdserver.pb.go

@@ -64,6 +64,8 @@
 		MemberUpdateResponse
 		MemberListRequest
 		MemberListResponse
+		MemberPromoteRequest
+		MemberPromoteResponse
 		DefragmentRequest
 		DefragmentResponse
 		MoveLeaderRequest

etcdserver/etcdserverpb/gw/rpc.pb.gw.go

@@ -341,6 +341,19 @@ func request_Cluster_MemberList_0(ctx context.Context, marshaler runtime.Marshal
 
 }
 
+func request_Cluster_MemberPromote_0(ctx context.Context, marshaler runtime.Marshaler, client etcdserverpb.ClusterClient, req *http.Request, pathParams map[string]string) (proto.Message, runtime.ServerMetadata, error) {
+	var protoReq etcdserverpb.MemberPromoteRequest
+	var metadata runtime.ServerMetadata
+
+	if err := marshaler.NewDecoder(req.Body).Decode(&protoReq); err != nil && err != io.EOF {
+		return nil, metadata, status.Errorf(codes.InvalidArgument, "%v", err)
+	}
+
+	msg, err := client.MemberPromote(ctx, &protoReq, grpc.Header(&metadata.HeaderMD), grpc.Trailer(&metadata.TrailerMD))
+	return msg, metadata, err
+
+}
+
 func request_Maintenance_Alarm_0(ctx context.Context, marshaler runtime.Marshaler, client etcdserverpb.MaintenanceClient, req *http.Request, pathParams map[string]string) (proto.Message, runtime.ServerMetadata, error) {
 	var protoReq etcdserverpb.AlarmRequest
 	var metadata runtime.ServerMetadata
@@ -1399,6 +1412,35 @@ func RegisterClusterHandlerClient(ctx context.Context, mux *runtime.ServeMux, cl
 
 	})
 
+	mux.Handle("POST", pattern_Cluster_MemberPromote_0, func(w http.ResponseWriter, req *http.Request, pathParams map[string]string) {
+		ctx, cancel := context.WithCancel(req.Context())
+		defer cancel()
+		if cn, ok := w.(http.CloseNotifier); ok {
+			go func(done <-chan struct{}, closed <-chan bool) {
+				select {
+				case <-done:
+				case <-closed:
+					cancel()
+				}
+			}(ctx.Done(), cn.CloseNotify())
+		}
+		inboundMarshaler, outboundMarshaler := runtime.MarshalerForRequest(mux, req)
+		rctx, err := runtime.AnnotateContext(ctx, mux, req)
+		if err != nil {
+			runtime.HTTPError(ctx, mux, outboundMarshaler, w, req, err)
+			return
+		}
+		resp, md, err := request_Cluster_MemberPromote_0(rctx, inboundMarshaler, client, req, pathParams)
+		ctx = runtime.NewServerMetadataContext(ctx, md)
+		if err != nil {
+			runtime.HTTPError(ctx, mux, outboundMarshaler, w, req, err)
+			return
+		}
+
+		forward_Cluster_MemberPromote_0(ctx, mux, outboundMarshaler, w, req, resp, mux.GetForwardResponseOptions()...)
+
+	})
+
 	return nil
 }
 
@@ -1410,6 +1452,8 @@ var (
 	pattern_Cluster_MemberUpdate_0 = runtime.MustPattern(runtime.NewPattern(1, []int{2, 0, 2, 1, 2, 2, 2, 3}, []string{"v3", "cluster", "member", "update"}, ""))
 
 	pattern_Cluster_MemberList_0 = runtime.MustPattern(runtime.NewPattern(1, []int{2, 0, 2, 1, 2, 2, 2, 3}, []string{"v3", "cluster", "member", "list"}, ""))
+
+	pattern_Cluster_MemberPromote_0 = runtime.MustPattern(runtime.NewPattern(1, []int{2, 0, 2, 1, 2, 2, 2, 3}, []string{"v3", "cluster", "member", "promote"}, ""))
 )
 
 var (
@@ -1420,6 +1464,8 @@ var (
 	forward_Cluster_MemberUpdate_0 = runtime.ForwardResponseMessage
 
 	forward_Cluster_MemberList_0 = runtime.ForwardResponseMessage
+
+	forward_Cluster_MemberPromote_0 = runtime.ForwardResponseMessage
 )
 
 // RegisterMaintenanceHandlerFromEndpoint is same as RegisterMaintenanceHandler but

etcdserver/etcdserverpb/rpc.proto

@@ -165,6 +165,14 @@ service Cluster {
         body: "*"
     };
   }
+
+  // MemberPromote promotes a member from raft learner (non-voting) to raft voting member.
+  rpc MemberPromote(MemberPromoteRequest) returns (MemberPromoteResponse) {
+      option (google.api.http) = {
+        post: "/v3/cluster/member/promote"
+        body: "*"
+    };
+  }
 }
 
 service Maintenance {
@@ -846,11 +854,15 @@ message Member {
   repeated string peerURLs = 3;
   // clientURLs is the list of URLs the member exposes to clients for communication. If the member is not started, clientURLs will be empty.
   repeated string clientURLs = 4;
+  // isLearner indicates if the member is raft learner.
+  bool isLearner = 5;
 }
 
 message MemberAddRequest {
   // peerURLs is the list of URLs the added member will use to communicate with the cluster.
   repeated string peerURLs = 1;
+  // isLearner indicates if the added member is raft learner.
+  bool isLearner = 2;
 }
 
 message MemberAddResponse {
@@ -894,6 +906,17 @@ message MemberListResponse {
   repeated Member members = 2;
 }
 
+message MemberPromoteRequest {
+  // ID is the member ID of the member to promote.
+  uint64 ID = 1;
+}
+
+message MemberPromoteResponse {
+  ResponseHeader header = 1;
+  // members is a list of all members after promoting the member.
+  repeated Member members = 2;
+}
+
 message DefragmentRequest {
 }
 
@@ -967,6 +990,8 @@ message StatusResponse {
   repeated string errors = 8;
   // dbSizeInUse is the size of the backend database logically in use, in bytes, of the responding member.
   int64 dbSizeInUse = 9;
+  // isLearner indicates if the member is raft learner.
+  bool isLearner = 10;
 }
 
 message AuthEnableRequest {

etcdserver/server.go

@@ -1544,6 +1544,7 @@ func (s *EtcdServer) AddMember(ctx context.Context, memb membership.Member) ([]*
 		return nil, err
 	}
 
+	// TODO: might switch to less strict check when adding raft learner
 	if s.Cfg.StrictReconfigCheck {
 		// by default StrictReconfigCheck is enabled; reject new members if unhealthy
 		if !s.cluster.IsReadyToAddNewMember() {
@@ -1585,6 +1586,11 @@ func (s *EtcdServer) AddMember(ctx context.Context, memb membership.Member) ([]*
 		NodeID:  uint64(memb.ID),
 		Context: b,
 	}
+
+	if memb.IsLearner {
+		cc.Type = raftpb.ConfChangeAddLearnerNode
+	}
+
 	return s.configure(ctx, cc)
 }
 
@@ -2054,7 +2060,7 @@ func (s *EtcdServer) applyConfChange(cc raftpb.ConfChange, confState *raftpb.Con
 	lg := s.getLogger()
 	*confState = *s.r.ApplyConfChange(cc)
 	switch cc.Type {
-	case raftpb.ConfChangeAddNode:
+	case raftpb.ConfChangeAddNode, raftpb.ConfChangeAddLearnerNode:
 		m := new(membership.Member)
 		if err := json.Unmarshal(cc.Context, m); err != nil {
 			if lg != nil {

proxy/grpcproxy/adapter/cluster_client_adapter.go

@@ -43,3 +43,7 @@ func (s *cls2clc) MemberUpdate(ctx context.Context, r *pb.MemberUpdateRequest, o
 func (s *cls2clc) MemberRemove(ctx context.Context, r *pb.MemberRemoveRequest, opts ...grpc.CallOption) (*pb.MemberRemoveResponse, error) {
 	return s.cls.MemberRemove(ctx, r)
 }
+
+func (s *cls2clc) MemberPromote(ctx context.Context, r *pb.MemberPromoteRequest, opts ...grpc.CallOption) (*pb.MemberPromoteResponse, error) {
+	return s.cls.MemberPromote(ctx, r)
+}

proxy/grpcproxy/cluster.go

@@ -16,6 +16,7 @@ package grpcproxy
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"os"
 	"sync"
@@ -108,7 +109,23 @@ func (cp *clusterProxy) monitor(wa gnaming.Watcher) {
 }
 
 func (cp *clusterProxy) MemberAdd(ctx context.Context, r *pb.MemberAddRequest) (*pb.MemberAddResponse, error) {
-	mresp, err := cp.clus.MemberAdd(ctx, r.PeerURLs)
+	if r.IsLearner {
+		return cp.memberAddAsLearner(ctx, r.PeerURLs)
+	}
+	return cp.memberAdd(ctx, r.PeerURLs)
+}
+
+func (cp *clusterProxy) memberAdd(ctx context.Context, peerURLs []string) (*pb.MemberAddResponse, error) {
+	mresp, err := cp.clus.MemberAdd(ctx, peerURLs)
+	if err != nil {
+		return nil, err
+	}
+	resp := (pb.MemberAddResponse)(*mresp)
+	return &resp, err
+}
+
+func (cp *clusterProxy) memberAddAsLearner(ctx context.Context, peerURLs []string) (*pb.MemberAddResponse, error) {
+	mresp, err := cp.clus.MemberAddAsLearner(ctx, peerURLs)
 	if err != nil {
 		return nil, err
 	}
@@ -175,3 +192,8 @@ func (cp *clusterProxy) MemberList(ctx context.Context, r *pb.MemberListRequest)
 	resp := (pb.MemberListResponse)(*mresp)
 	return &resp, err
 }
+
+func (cp *clusterProxy) MemberPromote(ctx context.Context, r *pb.MemberPromoteRequest) (*pb.MemberPromoteResponse, error) {
+	// TODO: implement
+	return nil, errors.New("not implemented")
+}

tests/e2e/ctl_v3_auth_test.go

@@ -510,13 +510,13 @@ func authTestMemberAdd(cx ctlCtx) {
 	peerURL := fmt.Sprintf("http://localhost:%d", etcdProcessBasePort+11)
 	// ordinary user cannot add a new member
 	cx.user, cx.pass = "test-user", "pass"
-	if err := ctlV3MemberAdd(cx, peerURL); err == nil {
+	if err := ctlV3MemberAdd(cx, peerURL, false); err == nil {
 		cx.t.Fatalf("ordinary user must not be allowed to add a member")
 	}
 
 	// root can add a new member
 	cx.user, cx.pass = "root", "root"
-	if err := ctlV3MemberAdd(cx, peerURL); err != nil {
+	if err := ctlV3MemberAdd(cx, peerURL, false); err != nil {
 		cx.t.Fatal(err)
 	}
 }

tests/e2e/ctl_v3_member_test.go

@@ -60,6 +60,7 @@ func TestCtlV3MemberAddClientAutoTLS(t *testing.T) {
 	testCtl(t, memberAddTest, withCfg(configClientAutoTLS))
 }
 func TestCtlV3MemberAddPeerTLS(t *testing.T)    { testCtl(t, memberAddTest, withCfg(configPeerTLS)) }
+func TestCtlV3MemberAddForLearner(t *testing.T) { testCtl(t, memberAddForLearnerTest) }
 func TestCtlV3MemberUpdate(t *testing.T)        { testCtl(t, memberUpdateTest) }
 func TestCtlV3MemberUpdateNoTLS(t *testing.T)   { testCtl(t, memberUpdateTest, withCfg(configNoTLS)) }
 func TestCtlV3MemberUpdateClientTLS(t *testing.T) {
@@ -122,13 +123,22 @@ func ctlV3MemberRemove(cx ctlCtx, ep, memberID, clusterID string) error {
 }
 
 func memberAddTest(cx ctlCtx) {
-	if err := ctlV3MemberAdd(cx, fmt.Sprintf("http://localhost:%d", etcdProcessBasePort+11)); err != nil {
+	if err := ctlV3MemberAdd(cx, fmt.Sprintf("http://localhost:%d", etcdProcessBasePort+11), false); err != nil {
 		cx.t.Fatal(err)
 	}
 }
 
-func ctlV3MemberAdd(cx ctlCtx, peerURL string) error {
+func memberAddForLearnerTest(cx ctlCtx) {
+	if err := ctlV3MemberAdd(cx, fmt.Sprintf("http://localhost:%d", etcdProcessBasePort+11), true); err != nil {
+		cx.t.Fatal(err)
+	}
+}
+
+func ctlV3MemberAdd(cx ctlCtx, peerURL string, isLearner bool) error {
 	cmdArgs := append(cx.PrefixArgs(), "member", "add", "newmember", fmt.Sprintf("--peer-urls=%s", peerURL))
+	if isLearner {
+		cmdArgs = append(cmdArgs, "--learner")
+	}
 	return spawnWithExpect(cmdArgs, " added to cluster ")
 }