diff --git a/vendor/google.golang.org/grpc/health/client.go b/vendor/google.golang.org/grpc/health/client.go
new file mode 100644
index 0000000..b43746e
--- /dev/null
+++ b/vendor/google.golang.org/grpc/health/client.go
@@ -0,0 +1,117 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package health
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"time"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/connectivity"
+	healthpb "google.golang.org/grpc/health/grpc_health_v1"
+	"google.golang.org/grpc/internal"
+	"google.golang.org/grpc/internal/backoff"
+	"google.golang.org/grpc/status"
+)
+
+const maxDelay = 120 * time.Second
+
+var backoffStrategy = backoff.Exponential{MaxDelay: maxDelay}
+var backoffFunc = func(ctx context.Context, retries int) bool {
+	d := backoffStrategy.Backoff(retries)
+	timer := time.NewTimer(d)
+	select {
+	case <-timer.C:
+		return true
+	case <-ctx.Done():
+		timer.Stop()
+		return false
+	}
+}
+
+func init() {
+	internal.HealthCheckFunc = clientHealthCheck
+}
+
+const healthCheckMethod = "/grpc.health.v1.Health/Watch"
+
+// This function implements the protocol defined at:
+// https://github.com/grpc/grpc/blob/master/doc/health-checking.md
+func clientHealthCheck(ctx context.Context, newStream func(string) (interface{}, error), setConnectivityState func(connectivity.State), service string) error {
+	tryCnt := 0
+
+retryConnection:
+	for {
+		// Backs off if the connection has failed in some way without receiving a message in the previous retry.
+		if tryCnt > 0 && !backoffFunc(ctx, tryCnt-1) {
+			return nil
+		}
+		tryCnt++
+
+		if ctx.Err() != nil {
+			return nil
+		}
+		setConnectivityState(connectivity.Connecting)
+		rawS, err := newStream(healthCheckMethod)
+		if err != nil {
+			continue retryConnection
+		}
+
+		s, ok := rawS.(grpc.ClientStream)
+		// Ideally, this should never happen. But if it happens, the server is marked as healthy for LBing purposes.
+		if !ok {
+			setConnectivityState(connectivity.Ready)
+			return fmt.Errorf("newStream returned %v (type %T); want grpc.ClientStream", rawS, rawS)
+		}
+
+		if err = s.SendMsg(&healthpb.HealthCheckRequest{Service: service}); err != nil && err != io.EOF {
+			// Stream should have been closed, so we can safely continue to create a new stream.
+			continue retryConnection
+		}
+		s.CloseSend()
+
+		resp := new(healthpb.HealthCheckResponse)
+		for {
+			err = s.RecvMsg(resp)
+
+			// Reports healthy for the LBing purposes if health check is not implemented in the server.
+			if status.Code(err) == codes.Unimplemented {
+				setConnectivityState(connectivity.Ready)
+				return err
+			}
+
+			// Reports unhealthy if server's Watch method gives an error other than UNIMPLEMENTED.
+			if err != nil {
+				setConnectivityState(connectivity.TransientFailure)
+				continue retryConnection
+			}
+
+			// As a message has been received, removes the need for backoff for the next retry by reseting the try count.
+			tryCnt = 0
+			if resp.Status == healthpb.HealthCheckResponse_SERVING {
+				setConnectivityState(connectivity.Ready)
+			} else {
+				setConnectivityState(connectivity.TransientFailure)
+			}
+		}
+	}
+}
diff --git a/vendor/google.golang.org/grpc/health/grpc_health_v1/health.pb.go b/vendor/google.golang.org/grpc/health/grpc_health_v1/health.pb.go
new file mode 100644
index 0000000..c99e27a
--- /dev/null
+++ b/vendor/google.golang.org/grpc/health/grpc_health_v1/health.pb.go
@@ -0,0 +1,343 @@
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// source: grpc/health/v1/health.proto
+
+package grpc_health_v1
+
+import (
+	context "context"
+	fmt "fmt"
+	proto "github.com/golang/protobuf/proto"
+	grpc "google.golang.org/grpc"
+	codes "google.golang.org/grpc/codes"
+	status "google.golang.org/grpc/status"
+	math "math"
+)
+
+// Reference imports to suppress errors if they are not otherwise used.
+var _ = proto.Marshal
+var _ = fmt.Errorf
+var _ = math.Inf
+
+// This is a compile-time assertion to ensure that this generated file
+// is compatible with the proto package it is being compiled against.
+// A compilation error at this line likely means your copy of the
+// proto package needs to be updated.
+const _ = proto.ProtoPackageIsVersion3 // please upgrade the proto package
+
+type HealthCheckResponse_ServingStatus int32
+
+const (
+	HealthCheckResponse_UNKNOWN         HealthCheckResponse_ServingStatus = 0
+	HealthCheckResponse_SERVING         HealthCheckResponse_ServingStatus = 1
+	HealthCheckResponse_NOT_SERVING     HealthCheckResponse_ServingStatus = 2
+	HealthCheckResponse_SERVICE_UNKNOWN HealthCheckResponse_ServingStatus = 3
+)
+
+var HealthCheckResponse_ServingStatus_name = map[int32]string{
+	0: "UNKNOWN",
+	1: "SERVING",
+	2: "NOT_SERVING",
+	3: "SERVICE_UNKNOWN",
+}
+
+var HealthCheckResponse_ServingStatus_value = map[string]int32{
+	"UNKNOWN":         0,
+	"SERVING":         1,
+	"NOT_SERVING":     2,
+	"SERVICE_UNKNOWN": 3,
+}
+
+func (x HealthCheckResponse_ServingStatus) String() string {
+	return proto.EnumName(HealthCheckResponse_ServingStatus_name, int32(x))
+}
+
+func (HealthCheckResponse_ServingStatus) EnumDescriptor() ([]byte, []int) {
+	return fileDescriptor_e265fd9d4e077217, []int{1, 0}
+}
+
+type HealthCheckRequest struct {
+	Service              string   `protobuf:"bytes,1,opt,name=service,proto3" json:"service,omitempty"`
+	XXX_NoUnkeyedLiteral struct{} `json:"-"`
+	XXX_unrecognized     []byte   `json:"-"`
+	XXX_sizecache        int32    `json:"-"`
+}
+
+func (m *HealthCheckRequest) Reset()         { *m = HealthCheckRequest{} }
+func (m *HealthCheckRequest) String() string { return proto.CompactTextString(m) }
+func (*HealthCheckRequest) ProtoMessage()    {}
+func (*HealthCheckRequest) Descriptor() ([]byte, []int) {
+	return fileDescriptor_e265fd9d4e077217, []int{0}
+}
+
+func (m *HealthCheckRequest) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_HealthCheckRequest.Unmarshal(m, b)
+}
+func (m *HealthCheckRequest) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_HealthCheckRequest.Marshal(b, m, deterministic)
+}
+func (m *HealthCheckRequest) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_HealthCheckRequest.Merge(m, src)
+}
+func (m *HealthCheckRequest) XXX_Size() int {
+	return xxx_messageInfo_HealthCheckRequest.Size(m)
+}
+func (m *HealthCheckRequest) XXX_DiscardUnknown() {
+	xxx_messageInfo_HealthCheckRequest.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_HealthCheckRequest proto.InternalMessageInfo
+
+func (m *HealthCheckRequest) GetService() string {
+	if m != nil {
+		return m.Service
+	}
+	return ""
+}
+
+type HealthCheckResponse struct {
+	Status               HealthCheckResponse_ServingStatus `protobuf:"varint,1,opt,name=status,proto3,enum=grpc.health.v1.HealthCheckResponse_ServingStatus" json:"status,omitempty"`
+	XXX_NoUnkeyedLiteral struct{}                          `json:"-"`
+	XXX_unrecognized     []byte                            `json:"-"`
+	XXX_sizecache        int32                             `json:"-"`
+}
+
+func (m *HealthCheckResponse) Reset()         { *m = HealthCheckResponse{} }
+func (m *HealthCheckResponse) String() string { return proto.CompactTextString(m) }
+func (*HealthCheckResponse) ProtoMessage()    {}
+func (*HealthCheckResponse) Descriptor() ([]byte, []int) {
+	return fileDescriptor_e265fd9d4e077217, []int{1}
+}
+
+func (m *HealthCheckResponse) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_HealthCheckResponse.Unmarshal(m, b)
+}
+func (m *HealthCheckResponse) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_HealthCheckResponse.Marshal(b, m, deterministic)
+}
+func (m *HealthCheckResponse) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_HealthCheckResponse.Merge(m, src)
+}
+func (m *HealthCheckResponse) XXX_Size() int {
+	return xxx_messageInfo_HealthCheckResponse.Size(m)
+}
+func (m *HealthCheckResponse) XXX_DiscardUnknown() {
+	xxx_messageInfo_HealthCheckResponse.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_HealthCheckResponse proto.InternalMessageInfo
+
+func (m *HealthCheckResponse) GetStatus() HealthCheckResponse_ServingStatus {
+	if m != nil {
+		return m.Status
+	}
+	return HealthCheckResponse_UNKNOWN
+}
+
+func init() {
+	proto.RegisterEnum("grpc.health.v1.HealthCheckResponse_ServingStatus", HealthCheckResponse_ServingStatus_name, HealthCheckResponse_ServingStatus_value)
+	proto.RegisterType((*HealthCheckRequest)(nil), "grpc.health.v1.HealthCheckRequest")
+	proto.RegisterType((*HealthCheckResponse)(nil), "grpc.health.v1.HealthCheckResponse")
+}
+
+func init() { proto.RegisterFile("grpc/health/v1/health.proto", fileDescriptor_e265fd9d4e077217) }
+
+var fileDescriptor_e265fd9d4e077217 = []byte{
+	// 297 bytes of a gzipped FileDescriptorProto
+	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xff, 0xe2, 0x92, 0x4e, 0x2f, 0x2a, 0x48,
+	0xd6, 0xcf, 0x48, 0x4d, 0xcc, 0x29, 0xc9, 0xd0, 0x2f, 0x33, 0x84, 0xb2, 0xf4, 0x0a, 0x8a, 0xf2,
+	0x4b, 0xf2, 0x85, 0xf8, 0x40, 0x92, 0x7a, 0x50, 0xa1, 0x32, 0x43, 0x25, 0x3d, 0x2e, 0x21, 0x0f,
+	0x30, 0xc7, 0x39, 0x23, 0x35, 0x39, 0x3b, 0x28, 0xb5, 0xb0, 0x34, 0xb5, 0xb8, 0x44, 0x48, 0x82,
+	0x8b, 0xbd, 0x38, 0xb5, 0xa8, 0x2c, 0x33, 0x39, 0x55, 0x82, 0x51, 0x81, 0x51, 0x83, 0x33, 0x08,
+	0xc6, 0x55, 0xda, 0xc8, 0xc8, 0x25, 0x8c, 0xa2, 0xa1, 0xb8, 0x20, 0x3f, 0xaf, 0x38, 0x55, 0xc8,
+	0x93, 0x8b, 0xad, 0xb8, 0x24, 0xb1, 0xa4, 0xb4, 0x18, 0xac, 0x81, 0xcf, 0xc8, 0x50, 0x0f, 0xd5,
+	0x22, 0x3d, 0x2c, 0x9a, 0xf4, 0x82, 0x41, 0x86, 0xe6, 0xa5, 0x07, 0x83, 0x35, 0x06, 0x41, 0x0d,
+	0x50, 0xf2, 0xe7, 0xe2, 0x45, 0x91, 0x10, 0xe2, 0xe6, 0x62, 0x0f, 0xf5, 0xf3, 0xf6, 0xf3, 0x0f,
+	0xf7, 0x13, 0x60, 0x00, 0x71, 0x82, 0x5d, 0x83, 0xc2, 0x3c, 0xfd, 0xdc, 0x05, 0x18, 0x85, 0xf8,
+	0xb9, 0xb8, 0xfd, 0xfc, 0x43, 0xe2, 0x61, 0x02, 0x4c, 0x42, 0xc2, 0x5c, 0xfc, 0x60, 0x8e, 0xb3,
+	0x6b, 0x3c, 0x4c, 0x0b, 0xb3, 0xd1, 0x3a, 0x46, 0x2e, 0x36, 0x88, 0xf5, 0x42, 0x01, 0x5c, 0xac,
+	0x60, 0x27, 0x08, 0x29, 0xe1, 0x75, 0x1f, 0x38, 0x14, 0xa4, 0x94, 0x89, 0xf0, 0x83, 0x50, 0x10,
+	0x17, 0x6b, 0x78, 0x62, 0x49, 0x72, 0x06, 0xd5, 0x4c, 0x34, 0x60, 0x74, 0x4a, 0xe4, 0x12, 0xcc,
+	0xcc, 0x47, 0x53, 0xea, 0xc4, 0x0d, 0x51, 0x1b, 0x00, 0x8a, 0xc6, 0x00, 0xc6, 0x28, 0x9d, 0xf4,
+	0xfc, 0xfc, 0xf4, 0x9c, 0x54, 0xbd, 0xf4, 0xfc, 0x9c, 0xc4, 0xbc, 0x74, 0xbd, 0xfc, 0xa2, 0x74,
+	0x7d, 0xe4, 0x78, 0x07, 0xb1, 0xe3, 0x21, 0xec, 0xf8, 0x32, 0xc3, 0x55, 0x4c, 0x7c, 0xee, 0x20,
+	0xd3, 0x20, 0x46, 0xe8, 0x85, 0x19, 0x26, 0xb1, 0x81, 0x93, 0x83, 0x31, 0x20, 0x00, 0x00, 0xff,
+	0xff, 0x12, 0x7d, 0x96, 0xcb, 0x2d, 0x02, 0x00, 0x00,
+}
+
+// Reference imports to suppress errors if they are not otherwise used.
+var _ context.Context
+var _ grpc.ClientConn
+
+// This is a compile-time assertion to ensure that this generated file
+// is compatible with the grpc package it is being compiled against.
+const _ = grpc.SupportPackageIsVersion4
+
+// HealthClient is the client API for Health service.
+//
+// For semantics around ctx use and closing/ending streaming RPCs, please refer to https://godoc.org/google.golang.org/grpc#ClientConn.NewStream.
+type HealthClient interface {
+	// If the requested service is unknown, the call will fail with status
+	// NOT_FOUND.
+	Check(ctx context.Context, in *HealthCheckRequest, opts ...grpc.CallOption) (*HealthCheckResponse, error)
+	// Performs a watch for the serving status of the requested service.
+	// The server will immediately send back a message indicating the current
+	// serving status.  It will then subsequently send a new message whenever
+	// the service's serving status changes.
+	//
+	// If the requested service is unknown when the call is received, the
+	// server will send a message setting the serving status to
+	// SERVICE_UNKNOWN but will *not* terminate the call.  If at some
+	// future point, the serving status of the service becomes known, the
+	// server will send a new message with the service's serving status.
+	//
+	// If the call terminates with status UNIMPLEMENTED, then clients
+	// should assume this method is not supported and should not retry the
+	// call.  If the call terminates with any other status (including OK),
+	// clients should retry the call with appropriate exponential backoff.
+	Watch(ctx context.Context, in *HealthCheckRequest, opts ...grpc.CallOption) (Health_WatchClient, error)
+}
+
+type healthClient struct {
+	cc *grpc.ClientConn
+}
+
+func NewHealthClient(cc *grpc.ClientConn) HealthClient {
+	return &healthClient{cc}
+}
+
+func (c *healthClient) Check(ctx context.Context, in *HealthCheckRequest, opts ...grpc.CallOption) (*HealthCheckResponse, error) {
+	out := new(HealthCheckResponse)
+	err := c.cc.Invoke(ctx, "/grpc.health.v1.Health/Check", in, out, opts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+func (c *healthClient) Watch(ctx context.Context, in *HealthCheckRequest, opts ...grpc.CallOption) (Health_WatchClient, error) {
+	stream, err := c.cc.NewStream(ctx, &_Health_serviceDesc.Streams[0], "/grpc.health.v1.Health/Watch", opts...)
+	if err != nil {
+		return nil, err
+	}
+	x := &healthWatchClient{stream}
+	if err := x.ClientStream.SendMsg(in); err != nil {
+		return nil, err
+	}
+	if err := x.ClientStream.CloseSend(); err != nil {
+		return nil, err
+	}
+	return x, nil
+}
+
+type Health_WatchClient interface {
+	Recv() (*HealthCheckResponse, error)
+	grpc.ClientStream
+}
+
+type healthWatchClient struct {
+	grpc.ClientStream
+}
+
+func (x *healthWatchClient) Recv() (*HealthCheckResponse, error) {
+	m := new(HealthCheckResponse)
+	if err := x.ClientStream.RecvMsg(m); err != nil {
+		return nil, err
+	}
+	return m, nil
+}
+
+// HealthServer is the server API for Health service.
+type HealthServer interface {
+	// If the requested service is unknown, the call will fail with status
+	// NOT_FOUND.
+	Check(context.Context, *HealthCheckRequest) (*HealthCheckResponse, error)
+	// Performs a watch for the serving status of the requested service.
+	// The server will immediately send back a message indicating the current
+	// serving status.  It will then subsequently send a new message whenever
+	// the service's serving status changes.
+	//
+	// If the requested service is unknown when the call is received, the
+	// server will send a message setting the serving status to
+	// SERVICE_UNKNOWN but will *not* terminate the call.  If at some
+	// future point, the serving status of the service becomes known, the
+	// server will send a new message with the service's serving status.
+	//
+	// If the call terminates with status UNIMPLEMENTED, then clients
+	// should assume this method is not supported and should not retry the
+	// call.  If the call terminates with any other status (including OK),
+	// clients should retry the call with appropriate exponential backoff.
+	Watch(*HealthCheckRequest, Health_WatchServer) error
+}
+
+// UnimplementedHealthServer can be embedded to have forward compatible implementations.
+type UnimplementedHealthServer struct {
+}
+
+func (*UnimplementedHealthServer) Check(ctx context.Context, req *HealthCheckRequest) (*HealthCheckResponse, error) {
+	return nil, status.Errorf(codes.Unimplemented, "method Check not implemented")
+}
+func (*UnimplementedHealthServer) Watch(req *HealthCheckRequest, srv Health_WatchServer) error {
+	return status.Errorf(codes.Unimplemented, "method Watch not implemented")
+}
+
+func RegisterHealthServer(s *grpc.Server, srv HealthServer) {
+	s.RegisterService(&_Health_serviceDesc, srv)
+}
+
+func _Health_Check_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(HealthCheckRequest)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(HealthServer).Check(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: "/grpc.health.v1.Health/Check",
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(HealthServer).Check(ctx, req.(*HealthCheckRequest))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
+func _Health_Watch_Handler(srv interface{}, stream grpc.ServerStream) error {
+	m := new(HealthCheckRequest)
+	if err := stream.RecvMsg(m); err != nil {
+		return err
+	}
+	return srv.(HealthServer).Watch(m, &healthWatchServer{stream})
+}
+
+type Health_WatchServer interface {
+	Send(*HealthCheckResponse) error
+	grpc.ServerStream
+}
+
+type healthWatchServer struct {
+	grpc.ServerStream
+}
+
+func (x *healthWatchServer) Send(m *HealthCheckResponse) error {
+	return x.ServerStream.SendMsg(m)
+}
+
+var _Health_serviceDesc = grpc.ServiceDesc{
+	ServiceName: "grpc.health.v1.Health",
+	HandlerType: (*HealthServer)(nil),
+	Methods: []grpc.MethodDesc{
+		{
+			MethodName: "Check",
+			Handler:    _Health_Check_Handler,
+		},
+	},
+	Streams: []grpc.StreamDesc{
+		{
+			StreamName:    "Watch",
+			Handler:       _Health_Watch_Handler,
+			ServerStreams: true,
+		},
+	},
+	Metadata: "grpc/health/v1/health.proto",
+}
diff --git a/vendor/google.golang.org/grpc/health/regenerate.sh b/vendor/google.golang.org/grpc/health/regenerate.sh
new file mode 100644
index 0000000..b11eccb
--- /dev/null
+++ b/vendor/google.golang.org/grpc/health/regenerate.sh
@@ -0,0 +1,33 @@
+#!/bin/bash
+# Copyright 2018 gRPC authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -eux -o pipefail
+
+TMP=$(mktemp -d)
+
+function finish {
+  rm -rf "$TMP"
+}
+trap finish EXIT
+
+pushd "$TMP"
+mkdir -p grpc/health/v1
+curl https://raw.githubusercontent.com/grpc/grpc-proto/master/grpc/health/v1/health.proto > grpc/health/v1/health.proto
+
+protoc --go_out=plugins=grpc,paths=source_relative:. -I. grpc/health/v1/*.proto
+popd
+rm -f grpc_health_v1/*.pb.go
+cp "$TMP"/grpc/health/v1/*.pb.go grpc_health_v1/
+
diff --git a/vendor/google.golang.org/grpc/health/server.go b/vendor/google.golang.org/grpc/health/server.go
new file mode 100644
index 0000000..c79f9d2
--- /dev/null
+++ b/vendor/google.golang.org/grpc/health/server.go
@@ -0,0 +1,165 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+//go:generate ./regenerate.sh
+
+// Package health provides a service that exposes server's health and it must be
+// imported to enable support for client-side health checks.
+package health
+
+import (
+	"context"
+	"sync"
+
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/grpclog"
+	healthgrpc "google.golang.org/grpc/health/grpc_health_v1"
+	healthpb "google.golang.org/grpc/health/grpc_health_v1"
+	"google.golang.org/grpc/status"
+)
+
+// Server implements `service Health`.
+type Server struct {
+	mu sync.Mutex
+	// If shutdown is true, it's expected all serving status is NOT_SERVING, and
+	// will stay in NOT_SERVING.
+	shutdown bool
+	// statusMap stores the serving status of the services this Server monitors.
+	statusMap map[string]healthpb.HealthCheckResponse_ServingStatus
+	updates   map[string]map[healthgrpc.Health_WatchServer]chan healthpb.HealthCheckResponse_ServingStatus
+}
+
+// NewServer returns a new Server.
+func NewServer() *Server {
+	return &Server{
+		statusMap: map[string]healthpb.HealthCheckResponse_ServingStatus{"": healthpb.HealthCheckResponse_SERVING},
+		updates:   make(map[string]map[healthgrpc.Health_WatchServer]chan healthpb.HealthCheckResponse_ServingStatus),
+	}
+}
+
+// Check implements `service Health`.
+func (s *Server) Check(ctx context.Context, in *healthpb.HealthCheckRequest) (*healthpb.HealthCheckResponse, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if servingStatus, ok := s.statusMap[in.Service]; ok {
+		return &healthpb.HealthCheckResponse{
+			Status: servingStatus,
+		}, nil
+	}
+	return nil, status.Error(codes.NotFound, "unknown service")
+}
+
+// Watch implements `service Health`.
+func (s *Server) Watch(in *healthpb.HealthCheckRequest, stream healthgrpc.Health_WatchServer) error {
+	service := in.Service
+	// update channel is used for getting service status updates.
+	update := make(chan healthpb.HealthCheckResponse_ServingStatus, 1)
+	s.mu.Lock()
+	// Puts the initial status to the channel.
+	if servingStatus, ok := s.statusMap[service]; ok {
+		update <- servingStatus
+	} else {
+		update <- healthpb.HealthCheckResponse_SERVICE_UNKNOWN
+	}
+
+	// Registers the update channel to the correct place in the updates map.
+	if _, ok := s.updates[service]; !ok {
+		s.updates[service] = make(map[healthgrpc.Health_WatchServer]chan healthpb.HealthCheckResponse_ServingStatus)
+	}
+	s.updates[service][stream] = update
+	defer func() {
+		s.mu.Lock()
+		delete(s.updates[service], stream)
+		s.mu.Unlock()
+	}()
+	s.mu.Unlock()
+
+	var lastSentStatus healthpb.HealthCheckResponse_ServingStatus = -1
+	for {
+		select {
+		// Status updated. Sends the up-to-date status to the client.
+		case servingStatus := <-update:
+			if lastSentStatus == servingStatus {
+				continue
+			}
+			lastSentStatus = servingStatus
+			err := stream.Send(&healthpb.HealthCheckResponse{Status: servingStatus})
+			if err != nil {
+				return status.Error(codes.Canceled, "Stream has ended.")
+			}
+		// Context done. Removes the update channel from the updates map.
+		case <-stream.Context().Done():
+			return status.Error(codes.Canceled, "Stream has ended.")
+		}
+	}
+}
+
+// SetServingStatus is called when need to reset the serving status of a service
+// or insert a new service entry into the statusMap.
+func (s *Server) SetServingStatus(service string, servingStatus healthpb.HealthCheckResponse_ServingStatus) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if s.shutdown {
+		grpclog.Infof("health: status changing for %s to %v is ignored because health service is shutdown", service, servingStatus)
+		return
+	}
+
+	s.setServingStatusLocked(service, servingStatus)
+}
+
+func (s *Server) setServingStatusLocked(service string, servingStatus healthpb.HealthCheckResponse_ServingStatus) {
+	s.statusMap[service] = servingStatus
+	for _, update := range s.updates[service] {
+		// Clears previous updates, that are not sent to the client, from the channel.
+		// This can happen if the client is not reading and the server gets flow control limited.
+		select {
+		case <-update:
+		default:
+		}
+		// Puts the most recent update to the channel.
+		update <- servingStatus
+	}
+}
+
+// Shutdown sets all serving status to NOT_SERVING, and configures the server to
+// ignore all future status changes.
+//
+// This changes serving status for all services. To set status for a perticular
+// services, call SetServingStatus().
+func (s *Server) Shutdown() {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.shutdown = true
+	for service := range s.statusMap {
+		s.setServingStatusLocked(service, healthpb.HealthCheckResponse_NOT_SERVING)
+	}
+}
+
+// Resume sets all serving status to SERVING, and configures the server to
+// accept all future status changes.
+//
+// This changes serving status for all services. To set status for a perticular
+// services, call SetServingStatus().
+func (s *Server) Resume() {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.shutdown = false
+	for service := range s.statusMap {
+		s.setServingStatusLocked(service, healthpb.HealthCheckResponse_SERVING)
+	}
+}