*: make MemberList linearizable

- Add linearizable field to etcdserverpb.MemberListRequest.
- Change behavior of clienv3 MemberList API. Now it is served with
linearizable guarantee.

CHANGELOG-3.5.md

@@ -21,6 +21,9 @@ See [code changes](https://github.com/etcd-io/etcd/compare/v3.4.0...v3.5.0) and
 
 ### Breaking Changes
 
+- Changed behavior of clienv3 API [MemberList](https://github.com/etcd-io/etcd/pull/11639).
+  - Previously, it is directly served with server's local data, which could be stale.
+  - Now, it is served with linearizable guarantee. If the server is disconnected from quorum, `MemberList` call will fail.
 - [gRPC gateway](https://github.com/grpc-ecosystem/grpc-gateway) only supports [`/v3`](TODO) endpoint.
   - Deprecated [`/v3beta`](https://github.com/etcd-io/etcd/pull/9298).
   - `curl -L http://localhost:2379/v3beta/kv/put -X POST -d '{"key": "Zm9v", "value": "YmFy"}'` does work in v3.5. Use `curl -L http://localhost:2379/v3/kv/put -X POST -d '{"key": "Zm9v", "value": "YmFy"}'` instead.
@@ -135,6 +138,7 @@ Note that any `etcd_debugging_*` metrics are experimental and subject to change.
 ### API
 
 - Add [`/v3/auth/status`](https://github.com/etcd-io/etcd/pull/11536) endpoint to check if authentication is enabled
+- [Add `Linearizable` field to `etcdserverpb.MemberListRequest`](https://github.com/etcd-io/etcd/pull/11639).
 
 
 ### Dependency

Documentation/dev-guide/api_reference_v3.md

@@ -670,7 +670,9 @@ Empty field.
 
 ##### message `MemberListRequest` (etcdserver/etcdserverpb/rpc.proto)
 
-Empty field.
+| Field | Description | Type |
+| ----- | ----------- | ---- |
+| linearizable |  | bool |
 
 
 

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

@@ -2365,7 +2365,13 @@
       }
     },
     "etcdserverpbMemberListRequest": {
-      "type": "object"
+      "type": "object",
+      "properties": {
+        "linearizable": {
+          "type": "boolean",
+          "format": "boolean"
+        }
+      }
     },
     "etcdserverpbMemberListResponse": {
       "type": "object",

clientv3/cluster.go

@@ -124,7 +124,7 @@ func (c *cluster) MemberUpdate(ctx context.Context, id uint64, peerAddrs []strin
 
 func (c *cluster) MemberList(ctx context.Context) (*MemberListResponse, error) {
 	// it is safe to retry on list.
-	resp, err := c.remote.MemberList(ctx, &pb.MemberListRequest{}, c.callOpts...)
+	resp, err := c.remote.MemberList(ctx, &pb.MemberListRequest{Linearizable: true}, c.callOpts...)
 	if err == nil {
 		return (*MemberListResponse)(resp), nil
 	}

etcdserver/api/v3rpc/member.go

@@ -28,10 +28,10 @@ import (
 
 type ClusterServer struct {
 	cluster api.Cluster
-	server  etcdserver.ServerV3
+	server  *etcdserver.EtcdServer
 }
 
-func NewClusterServer(s etcdserver.ServerV3) *ClusterServer {
+func NewClusterServer(s *etcdserver.EtcdServer) *ClusterServer {
 	return &ClusterServer{
 		cluster: s.Cluster(),
 		server:  s,
@@ -88,6 +88,11 @@ func (cs *ClusterServer) MemberUpdate(ctx context.Context, r *pb.MemberUpdateReq
 }
 
 func (cs *ClusterServer) MemberList(ctx context.Context, r *pb.MemberListRequest) (*pb.MemberListResponse, error) {
+	if r.Linearizable {
+		if err := cs.server.LinearizableReadNotify(ctx); err != nil {
+			return nil, togRPCError(err)
+		}
+	}
 	membs := membersToProtoMembers(cs.cluster.Members())
 	return &pb.MemberListResponse{Header: cs.header(), Members: membs}, nil
 }

etcdserver/etcdserverpb/rpc.proto

@@ -914,6 +914,7 @@ message MemberUpdateResponse{
 }
 
 message MemberListRequest {
+  bool linearizable = 1;
 }
 
 message MemberListResponse {

etcdserver/v3_server.go

@@ -758,6 +758,10 @@ func (s *EtcdServer) linearizableReadLoop() {
 	}
 }
 
+func (s *EtcdServer) LinearizableReadNotify(ctx context.Context) error {
+	return s.linearizableReadNotify(ctx)
+}
+
 func (s *EtcdServer) linearizableReadNotify(ctx context.Context) error {
 	s.readMu.RLock()
 	nc := s.readNotifier