diff --git a/vendor/go.etcd.io/etcd/clientv3/watch.go b/vendor/go.etcd.io/etcd/clientv3/watch.go
new file mode 100644
index 0000000..87d222d
--- /dev/null
+++ b/vendor/go.etcd.io/etcd/clientv3/watch.go
@@ -0,0 +1,987 @@
+// Copyright 2016 The etcd 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 clientv3
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"sync"
+	"time"
+
+	v3rpc "go.etcd.io/etcd/etcdserver/api/v3rpc/rpctypes"
+	pb "go.etcd.io/etcd/etcdserver/etcdserverpb"
+	mvccpb "go.etcd.io/etcd/mvcc/mvccpb"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/metadata"
+	"google.golang.org/grpc/status"
+)
+
+const (
+	EventTypeDelete = mvccpb.DELETE
+	EventTypePut    = mvccpb.PUT
+
+	closeSendErrTimeout = 250 * time.Millisecond
+)
+
+type Event mvccpb.Event
+
+type WatchChan <-chan WatchResponse
+
+type Watcher interface {
+	// Watch watches on a key or prefix. The watched events will be returned
+	// through the returned channel. If revisions waiting to be sent over the
+	// watch are compacted, then the watch will be canceled by the server, the
+	// client will post a compacted error watch response, and the channel will close.
+	// If the context "ctx" is canceled or timed out, returned "WatchChan" is closed,
+	// and "WatchResponse" from this closed channel has zero events and nil "Err()".
+	// The context "ctx" MUST be canceled, as soon as watcher is no longer being used,
+	// to release the associated resources.
+	//
+	// If the context is "context.Background/TODO", returned "WatchChan" will
+	// not be closed and block until event is triggered, except when server
+	// returns a non-recoverable error (e.g. ErrCompacted).
+	// For example, when context passed with "WithRequireLeader" and the
+	// connected server has no leader (e.g. due to network partition),
+	// error "etcdserver: no leader" (ErrNoLeader) will be returned,
+	// and then "WatchChan" is closed with non-nil "Err()".
+	// In order to prevent a watch stream being stuck in a partitioned node,
+	// make sure to wrap context with "WithRequireLeader".
+	//
+	// Otherwise, as long as the context has not been canceled or timed out,
+	// watch will retry on other recoverable errors forever until reconnected.
+	//
+	// TODO: explicitly set context error in the last "WatchResponse" message and close channel?
+	// Currently, client contexts are overwritten with "valCtx" that never closes.
+	// TODO(v3.4): configure watch retry policy, limit maximum retry number
+	// (see https://github.com/etcd-io/etcd/issues/8980)
+	Watch(ctx context.Context, key string, opts ...OpOption) WatchChan
+
+	// RequestProgress requests a progress notify response be sent in all watch channels.
+	RequestProgress(ctx context.Context) error
+
+	// Close closes the watcher and cancels all watch requests.
+	Close() error
+}
+
+type WatchResponse struct {
+	Header pb.ResponseHeader
+	Events []*Event
+
+	// CompactRevision is the minimum revision the watcher may receive.
+	CompactRevision int64
+
+	// Canceled is used to indicate watch failure.
+	// If the watch failed and the stream was about to close, before the channel is closed,
+	// the channel sends a final response that has Canceled set to true with a non-nil Err().
+	Canceled bool
+
+	// Created is used to indicate the creation of the watcher.
+	Created bool
+
+	closeErr error
+
+	// cancelReason is a reason of canceling watch
+	cancelReason string
+}
+
+// IsCreate returns true if the event tells that the key is newly created.
+func (e *Event) IsCreate() bool {
+	return e.Type == EventTypePut && e.Kv.CreateRevision == e.Kv.ModRevision
+}
+
+// IsModify returns true if the event tells that a new value is put on existing key.
+func (e *Event) IsModify() bool {
+	return e.Type == EventTypePut && e.Kv.CreateRevision != e.Kv.ModRevision
+}
+
+// Err is the error value if this WatchResponse holds an error.
+func (wr *WatchResponse) Err() error {
+	switch {
+	case wr.closeErr != nil:
+		return v3rpc.Error(wr.closeErr)
+	case wr.CompactRevision != 0:
+		return v3rpc.ErrCompacted
+	case wr.Canceled:
+		if len(wr.cancelReason) != 0 {
+			return v3rpc.Error(status.Error(codes.FailedPrecondition, wr.cancelReason))
+		}
+		return v3rpc.ErrFutureRev
+	}
+	return nil
+}
+
+// IsProgressNotify returns true if the WatchResponse is progress notification.
+func (wr *WatchResponse) IsProgressNotify() bool {
+	return len(wr.Events) == 0 && !wr.Canceled && !wr.Created && wr.CompactRevision == 0 && wr.Header.Revision != 0
+}
+
+// watcher implements the Watcher interface
+type watcher struct {
+	remote   pb.WatchClient
+	callOpts []grpc.CallOption
+
+	// mu protects the grpc streams map
+	mu sync.RWMutex
+
+	// streams holds all the active grpc streams keyed by ctx value.
+	streams map[string]*watchGrpcStream
+}
+
+// watchGrpcStream tracks all watch resources attached to a single grpc stream.
+type watchGrpcStream struct {
+	owner    *watcher
+	remote   pb.WatchClient
+	callOpts []grpc.CallOption
+
+	// ctx controls internal remote.Watch requests
+	ctx context.Context
+	// ctxKey is the key used when looking up this stream's context
+	ctxKey string
+	cancel context.CancelFunc
+
+	// substreams holds all active watchers on this grpc stream
+	substreams map[int64]*watcherStream
+	// resuming holds all resuming watchers on this grpc stream
+	resuming []*watcherStream
+
+	// reqc sends a watch request from Watch() to the main goroutine
+	reqc chan watchStreamRequest
+	// respc receives data from the watch client
+	respc chan *pb.WatchResponse
+	// donec closes to broadcast shutdown
+	donec chan struct{}
+	// errc transmits errors from grpc Recv to the watch stream reconnect logic
+	errc chan error
+	// closingc gets the watcherStream of closing watchers
+	closingc chan *watcherStream
+	// wg is Done when all substream goroutines have exited
+	wg sync.WaitGroup
+
+	// resumec closes to signal that all substreams should begin resuming
+	resumec chan struct{}
+	// closeErr is the error that closed the watch stream
+	closeErr error
+}
+
+// watchStreamRequest is a union of the supported watch request operation types
+type watchStreamRequest interface {
+	toPB() *pb.WatchRequest
+}
+
+// watchRequest is issued by the subscriber to start a new watcher
+type watchRequest struct {
+	ctx context.Context
+	key string
+	end string
+	rev int64
+
+	// send created notification event if this field is true
+	createdNotify bool
+	// progressNotify is for progress updates
+	progressNotify bool
+	// fragmentation should be disabled by default
+	// if true, split watch events when total exceeds
+	// "--max-request-bytes" flag value + 512-byte
+	fragment bool
+
+	// filters is the list of events to filter out
+	filters []pb.WatchCreateRequest_FilterType
+	// get the previous key-value pair before the event happens
+	prevKV bool
+	// retc receives a chan WatchResponse once the watcher is established
+	retc chan chan WatchResponse
+}
+
+// progressRequest is issued by the subscriber to request watch progress
+type progressRequest struct {
+}
+
+// watcherStream represents a registered watcher
+type watcherStream struct {
+	// initReq is the request that initiated this request
+	initReq watchRequest
+
+	// outc publishes watch responses to subscriber
+	outc chan WatchResponse
+	// recvc buffers watch responses before publishing
+	recvc chan *WatchResponse
+	// donec closes when the watcherStream goroutine stops.
+	donec chan struct{}
+	// closing is set to true when stream should be scheduled to shutdown.
+	closing bool
+	// id is the registered watch id on the grpc stream
+	id int64
+
+	// buf holds all events received from etcd but not yet consumed by the client
+	buf []*WatchResponse
+}
+
+func NewWatcher(c *Client) Watcher {
+	return NewWatchFromWatchClient(pb.NewWatchClient(c.conn), c)
+}
+
+func NewWatchFromWatchClient(wc pb.WatchClient, c *Client) Watcher {
+	w := &watcher{
+		remote:  wc,
+		streams: make(map[string]*watchGrpcStream),
+	}
+	if c != nil {
+		w.callOpts = c.callOpts
+	}
+	return w
+}
+
+// never closes
+var valCtxCh = make(chan struct{})
+var zeroTime = time.Unix(0, 0)
+
+// ctx with only the values; never Done
+type valCtx struct{ context.Context }
+
+func (vc *valCtx) Deadline() (time.Time, bool) { return zeroTime, false }
+func (vc *valCtx) Done() <-chan struct{}       { return valCtxCh }
+func (vc *valCtx) Err() error                  { return nil }
+
+func (w *watcher) newWatcherGrpcStream(inctx context.Context) *watchGrpcStream {
+	ctx, cancel := context.WithCancel(&valCtx{inctx})
+	wgs := &watchGrpcStream{
+		owner:      w,
+		remote:     w.remote,
+		callOpts:   w.callOpts,
+		ctx:        ctx,
+		ctxKey:     streamKeyFromCtx(inctx),
+		cancel:     cancel,
+		substreams: make(map[int64]*watcherStream),
+		respc:      make(chan *pb.WatchResponse),
+		reqc:       make(chan watchStreamRequest),
+		donec:      make(chan struct{}),
+		errc:       make(chan error, 1),
+		closingc:   make(chan *watcherStream),
+		resumec:    make(chan struct{}),
+	}
+	go wgs.run()
+	return wgs
+}
+
+// Watch posts a watch request to run() and waits for a new watcher channel
+func (w *watcher) Watch(ctx context.Context, key string, opts ...OpOption) WatchChan {
+	ow := opWatch(key, opts...)
+
+	var filters []pb.WatchCreateRequest_FilterType
+	if ow.filterPut {
+		filters = append(filters, pb.WatchCreateRequest_NOPUT)
+	}
+	if ow.filterDelete {
+		filters = append(filters, pb.WatchCreateRequest_NODELETE)
+	}
+
+	wr := &watchRequest{
+		ctx:            ctx,
+		createdNotify:  ow.createdNotify,
+		key:            string(ow.key),
+		end:            string(ow.end),
+		rev:            ow.rev,
+		progressNotify: ow.progressNotify,
+		fragment:       ow.fragment,
+		filters:        filters,
+		prevKV:         ow.prevKV,
+		retc:           make(chan chan WatchResponse, 1),
+	}
+
+	ok := false
+	ctxKey := streamKeyFromCtx(ctx)
+
+	// find or allocate appropriate grpc watch stream
+	w.mu.Lock()
+	if w.streams == nil {
+		// closed
+		w.mu.Unlock()
+		ch := make(chan WatchResponse)
+		close(ch)
+		return ch
+	}
+	wgs := w.streams[ctxKey]
+	if wgs == nil {
+		wgs = w.newWatcherGrpcStream(ctx)
+		w.streams[ctxKey] = wgs
+	}
+	donec := wgs.donec
+	reqc := wgs.reqc
+	w.mu.Unlock()
+
+	// couldn't create channel; return closed channel
+	closeCh := make(chan WatchResponse, 1)
+
+	// submit request
+	select {
+	case reqc <- wr:
+		ok = true
+	case <-wr.ctx.Done():
+	case <-donec:
+		if wgs.closeErr != nil {
+			closeCh <- WatchResponse{Canceled: true, closeErr: wgs.closeErr}
+			break
+		}
+		// retry; may have dropped stream from no ctxs
+		return w.Watch(ctx, key, opts...)
+	}
+
+	// receive channel
+	if ok {
+		select {
+		case ret := <-wr.retc:
+			return ret
+		case <-ctx.Done():
+		case <-donec:
+			if wgs.closeErr != nil {
+				closeCh <- WatchResponse{Canceled: true, closeErr: wgs.closeErr}
+				break
+			}
+			// retry; may have dropped stream from no ctxs
+			return w.Watch(ctx, key, opts...)
+		}
+	}
+
+	close(closeCh)
+	return closeCh
+}
+
+func (w *watcher) Close() (err error) {
+	w.mu.Lock()
+	streams := w.streams
+	w.streams = nil
+	w.mu.Unlock()
+	for _, wgs := range streams {
+		if werr := wgs.close(); werr != nil {
+			err = werr
+		}
+	}
+	// Consider context.Canceled as a successful close
+	if err == context.Canceled {
+		err = nil
+	}
+	return err
+}
+
+// RequestProgress requests a progress notify response be sent in all watch channels.
+func (w *watcher) RequestProgress(ctx context.Context) (err error) {
+	ctxKey := streamKeyFromCtx(ctx)
+
+	w.mu.Lock()
+	if w.streams == nil {
+		w.mu.Unlock()
+		return fmt.Errorf("no stream found for context")
+	}
+	wgs := w.streams[ctxKey]
+	if wgs == nil {
+		wgs = w.newWatcherGrpcStream(ctx)
+		w.streams[ctxKey] = wgs
+	}
+	donec := wgs.donec
+	reqc := wgs.reqc
+	w.mu.Unlock()
+
+	pr := &progressRequest{}
+
+	select {
+	case reqc <- pr:
+		return nil
+	case <-ctx.Done():
+		if err == nil {
+			return ctx.Err()
+		}
+		return err
+	case <-donec:
+		if wgs.closeErr != nil {
+			return wgs.closeErr
+		}
+		// retry; may have dropped stream from no ctxs
+		return w.RequestProgress(ctx)
+	}
+}
+
+func (w *watchGrpcStream) close() (err error) {
+	w.cancel()
+	<-w.donec
+	select {
+	case err = <-w.errc:
+	default:
+	}
+	return toErr(w.ctx, err)
+}
+
+func (w *watcher) closeStream(wgs *watchGrpcStream) {
+	w.mu.Lock()
+	close(wgs.donec)
+	wgs.cancel()
+	if w.streams != nil {
+		delete(w.streams, wgs.ctxKey)
+	}
+	w.mu.Unlock()
+}
+
+func (w *watchGrpcStream) addSubstream(resp *pb.WatchResponse, ws *watcherStream) {
+	// check watch ID for backward compatibility (<= v3.3)
+	if resp.WatchId == -1 || (resp.Canceled && resp.CancelReason != "") {
+		w.closeErr = v3rpc.Error(errors.New(resp.CancelReason))
+		// failed; no channel
+		close(ws.recvc)
+		return
+	}
+	ws.id = resp.WatchId
+	w.substreams[ws.id] = ws
+}
+
+func (w *watchGrpcStream) sendCloseSubstream(ws *watcherStream, resp *WatchResponse) {
+	select {
+	case ws.outc <- *resp:
+	case <-ws.initReq.ctx.Done():
+	case <-time.After(closeSendErrTimeout):
+	}
+	close(ws.outc)
+}
+
+func (w *watchGrpcStream) closeSubstream(ws *watcherStream) {
+	// send channel response in case stream was never established
+	select {
+	case ws.initReq.retc <- ws.outc:
+	default:
+	}
+	// close subscriber's channel
+	if closeErr := w.closeErr; closeErr != nil && ws.initReq.ctx.Err() == nil {
+		go w.sendCloseSubstream(ws, &WatchResponse{Canceled: true, closeErr: w.closeErr})
+	} else if ws.outc != nil {
+		close(ws.outc)
+	}
+	if ws.id != -1 {
+		delete(w.substreams, ws.id)
+		return
+	}
+	for i := range w.resuming {
+		if w.resuming[i] == ws {
+			w.resuming[i] = nil
+			return
+		}
+	}
+}
+
+// run is the root of the goroutines for managing a watcher client
+func (w *watchGrpcStream) run() {
+	var wc pb.Watch_WatchClient
+	var closeErr error
+
+	// substreams marked to close but goroutine still running; needed for
+	// avoiding double-closing recvc on grpc stream teardown
+	closing := make(map[*watcherStream]struct{})
+
+	defer func() {
+		w.closeErr = closeErr
+		// shutdown substreams and resuming substreams
+		for _, ws := range w.substreams {
+			if _, ok := closing[ws]; !ok {
+				close(ws.recvc)
+				closing[ws] = struct{}{}
+			}
+		}
+		for _, ws := range w.resuming {
+			if _, ok := closing[ws]; ws != nil && !ok {
+				close(ws.recvc)
+				closing[ws] = struct{}{}
+			}
+		}
+		w.joinSubstreams()
+		for range closing {
+			w.closeSubstream(<-w.closingc)
+		}
+		w.wg.Wait()
+		w.owner.closeStream(w)
+	}()
+
+	// start a stream with the etcd grpc server
+	if wc, closeErr = w.newWatchClient(); closeErr != nil {
+		return
+	}
+
+	cancelSet := make(map[int64]struct{})
+
+	var cur *pb.WatchResponse
+	for {
+		select {
+		// Watch() requested
+		case req := <-w.reqc:
+			switch wreq := req.(type) {
+			case *watchRequest:
+				outc := make(chan WatchResponse, 1)
+				// TODO: pass custom watch ID?
+				ws := &watcherStream{
+					initReq: *wreq,
+					id:      -1,
+					outc:    outc,
+					// unbuffered so resumes won't cause repeat events
+					recvc: make(chan *WatchResponse),
+				}
+
+				ws.donec = make(chan struct{})
+				w.wg.Add(1)
+				go w.serveSubstream(ws, w.resumec)
+
+				// queue up for watcher creation/resume
+				w.resuming = append(w.resuming, ws)
+				if len(w.resuming) == 1 {
+					// head of resume queue, can register a new watcher
+					wc.Send(ws.initReq.toPB())
+				}
+			case *progressRequest:
+				wc.Send(wreq.toPB())
+			}
+
+		// new events from the watch client
+		case pbresp := <-w.respc:
+			if cur == nil || pbresp.Created || pbresp.Canceled {
+				cur = pbresp
+			} else if cur != nil && cur.WatchId == pbresp.WatchId {
+				// merge new events
+				cur.Events = append(cur.Events, pbresp.Events...)
+				// update "Fragment" field; last response with "Fragment" == false
+				cur.Fragment = pbresp.Fragment
+			}
+
+			switch {
+			case pbresp.Created:
+				// response to head of queue creation
+				if ws := w.resuming[0]; ws != nil {
+					w.addSubstream(pbresp, ws)
+					w.dispatchEvent(pbresp)
+					w.resuming[0] = nil
+				}
+
+				if ws := w.nextResume(); ws != nil {
+					wc.Send(ws.initReq.toPB())
+				}
+
+				// reset for next iteration
+				cur = nil
+
+			case pbresp.Canceled && pbresp.CompactRevision == 0:
+				delete(cancelSet, pbresp.WatchId)
+				if ws, ok := w.substreams[pbresp.WatchId]; ok {
+					// signal to stream goroutine to update closingc
+					close(ws.recvc)
+					closing[ws] = struct{}{}
+				}
+
+				// reset for next iteration
+				cur = nil
+
+			case cur.Fragment:
+				// watch response events are still fragmented
+				// continue to fetch next fragmented event arrival
+				continue
+
+			default:
+				// dispatch to appropriate watch stream
+				ok := w.dispatchEvent(cur)
+
+				// reset for next iteration
+				cur = nil
+
+				if ok {
+					break
+				}
+
+				// watch response on unexpected watch id; cancel id
+				if _, ok := cancelSet[pbresp.WatchId]; ok {
+					break
+				}
+
+				cancelSet[pbresp.WatchId] = struct{}{}
+				cr := &pb.WatchRequest_CancelRequest{
+					CancelRequest: &pb.WatchCancelRequest{
+						WatchId: pbresp.WatchId,
+					},
+				}
+				req := &pb.WatchRequest{RequestUnion: cr}
+				wc.Send(req)
+			}
+
+		// watch client failed on Recv; spawn another if possible
+		case err := <-w.errc:
+			if isHaltErr(w.ctx, err) || toErr(w.ctx, err) == v3rpc.ErrNoLeader {
+				closeErr = err
+				return
+			}
+			if wc, closeErr = w.newWatchClient(); closeErr != nil {
+				return
+			}
+			if ws := w.nextResume(); ws != nil {
+				wc.Send(ws.initReq.toPB())
+			}
+			cancelSet = make(map[int64]struct{})
+
+		case <-w.ctx.Done():
+			return
+
+		case ws := <-w.closingc:
+			w.closeSubstream(ws)
+			delete(closing, ws)
+			// no more watchers on this stream, shutdown
+			if len(w.substreams)+len(w.resuming) == 0 {
+				return
+			}
+		}
+	}
+}
+
+// nextResume chooses the next resuming to register with the grpc stream. Abandoned
+// streams are marked as nil in the queue since the head must wait for its inflight registration.
+func (w *watchGrpcStream) nextResume() *watcherStream {
+	for len(w.resuming) != 0 {
+		if w.resuming[0] != nil {
+			return w.resuming[0]
+		}
+		w.resuming = w.resuming[1:len(w.resuming)]
+	}
+	return nil
+}
+
+// dispatchEvent sends a WatchResponse to the appropriate watcher stream
+func (w *watchGrpcStream) dispatchEvent(pbresp *pb.WatchResponse) bool {
+	events := make([]*Event, len(pbresp.Events))
+	for i, ev := range pbresp.Events {
+		events[i] = (*Event)(ev)
+	}
+	// TODO: return watch ID?
+	wr := &WatchResponse{
+		Header:          *pbresp.Header,
+		Events:          events,
+		CompactRevision: pbresp.CompactRevision,
+		Created:         pbresp.Created,
+		Canceled:        pbresp.Canceled,
+		cancelReason:    pbresp.CancelReason,
+	}
+
+	// watch IDs are zero indexed, so request notify watch responses are assigned a watch ID of -1 to
+	// indicate they should be broadcast.
+	if wr.IsProgressNotify() && pbresp.WatchId == -1 {
+		return w.broadcastResponse(wr)
+	}
+
+	return w.unicastResponse(wr, pbresp.WatchId)
+
+}
+
+// broadcastResponse send a watch response to all watch substreams.
+func (w *watchGrpcStream) broadcastResponse(wr *WatchResponse) bool {
+	for _, ws := range w.substreams {
+		select {
+		case ws.recvc <- wr:
+		case <-ws.donec:
+		}
+	}
+	return true
+}
+
+// unicastResponse sends a watch response to a specific watch substream.
+func (w *watchGrpcStream) unicastResponse(wr *WatchResponse, watchId int64) bool {
+	ws, ok := w.substreams[watchId]
+	if !ok {
+		return false
+	}
+	select {
+	case ws.recvc <- wr:
+	case <-ws.donec:
+		return false
+	}
+	return true
+}
+
+// serveWatchClient forwards messages from the grpc stream to run()
+func (w *watchGrpcStream) serveWatchClient(wc pb.Watch_WatchClient) {
+	for {
+		resp, err := wc.Recv()
+		if err != nil {
+			select {
+			case w.errc <- err:
+			case <-w.donec:
+			}
+			return
+		}
+		select {
+		case w.respc <- resp:
+		case <-w.donec:
+			return
+		}
+	}
+}
+
+// serveSubstream forwards watch responses from run() to the subscriber
+func (w *watchGrpcStream) serveSubstream(ws *watcherStream, resumec chan struct{}) {
+	if ws.closing {
+		panic("created substream goroutine but substream is closing")
+	}
+
+	// nextRev is the minimum expected next revision
+	nextRev := ws.initReq.rev
+	resuming := false
+	defer func() {
+		if !resuming {
+			ws.closing = true
+		}
+		close(ws.donec)
+		if !resuming {
+			w.closingc <- ws
+		}
+		w.wg.Done()
+	}()
+
+	emptyWr := &WatchResponse{}
+	for {
+		curWr := emptyWr
+		outc := ws.outc
+
+		if len(ws.buf) > 0 {
+			curWr = ws.buf[0]
+		} else {
+			outc = nil
+		}
+		select {
+		case outc <- *curWr:
+			if ws.buf[0].Err() != nil {
+				return
+			}
+			ws.buf[0] = nil
+			ws.buf = ws.buf[1:]
+		case wr, ok := <-ws.recvc:
+			if !ok {
+				// shutdown from closeSubstream
+				return
+			}
+
+			if wr.Created {
+				if ws.initReq.retc != nil {
+					ws.initReq.retc <- ws.outc
+					// to prevent next write from taking the slot in buffered channel
+					// and posting duplicate create events
+					ws.initReq.retc = nil
+
+					// send first creation event only if requested
+					if ws.initReq.createdNotify {
+						ws.outc <- *wr
+					}
+					// once the watch channel is returned, a current revision
+					// watch must resume at the store revision. This is necessary
+					// for the following case to work as expected:
+					//	wch := m1.Watch("a")
+					//	m2.Put("a", "b")
+					//	<-wch
+					// If the revision is only bound on the first observed event,
+					// if wch is disconnected before the Put is issued, then reconnects
+					// after it is committed, it'll miss the Put.
+					if ws.initReq.rev == 0 {
+						nextRev = wr.Header.Revision
+					}
+				}
+			} else {
+				// current progress of watch; <= store revision
+				nextRev = wr.Header.Revision
+			}
+
+			if len(wr.Events) > 0 {
+				nextRev = wr.Events[len(wr.Events)-1].Kv.ModRevision + 1
+			}
+			ws.initReq.rev = nextRev
+
+			// created event is already sent above,
+			// watcher should not post duplicate events
+			if wr.Created {
+				continue
+			}
+
+			// TODO pause channel if buffer gets too large
+			ws.buf = append(ws.buf, wr)
+		case <-w.ctx.Done():
+			return
+		case <-ws.initReq.ctx.Done():
+			return
+		case <-resumec:
+			resuming = true
+			return
+		}
+	}
+	// lazily send cancel message if events on missing id
+}
+
+func (w *watchGrpcStream) newWatchClient() (pb.Watch_WatchClient, error) {
+	// mark all substreams as resuming
+	close(w.resumec)
+	w.resumec = make(chan struct{})
+	w.joinSubstreams()
+	for _, ws := range w.substreams {
+		ws.id = -1
+		w.resuming = append(w.resuming, ws)
+	}
+	// strip out nils, if any
+	var resuming []*watcherStream
+	for _, ws := range w.resuming {
+		if ws != nil {
+			resuming = append(resuming, ws)
+		}
+	}
+	w.resuming = resuming
+	w.substreams = make(map[int64]*watcherStream)
+
+	// connect to grpc stream while accepting watcher cancelation
+	stopc := make(chan struct{})
+	donec := w.waitCancelSubstreams(stopc)
+	wc, err := w.openWatchClient()
+	close(stopc)
+	<-donec
+
+	// serve all non-closing streams, even if there's a client error
+	// so that the teardown path can shutdown the streams as expected.
+	for _, ws := range w.resuming {
+		if ws.closing {
+			continue
+		}
+		ws.donec = make(chan struct{})
+		w.wg.Add(1)
+		go w.serveSubstream(ws, w.resumec)
+	}
+
+	if err != nil {
+		return nil, v3rpc.Error(err)
+	}
+
+	// receive data from new grpc stream
+	go w.serveWatchClient(wc)
+	return wc, nil
+}
+
+func (w *watchGrpcStream) waitCancelSubstreams(stopc <-chan struct{}) <-chan struct{} {
+	var wg sync.WaitGroup
+	wg.Add(len(w.resuming))
+	donec := make(chan struct{})
+	for i := range w.resuming {
+		go func(ws *watcherStream) {
+			defer wg.Done()
+			if ws.closing {
+				if ws.initReq.ctx.Err() != nil && ws.outc != nil {
+					close(ws.outc)
+					ws.outc = nil
+				}
+				return
+			}
+			select {
+			case <-ws.initReq.ctx.Done():
+				// closed ws will be removed from resuming
+				ws.closing = true
+				close(ws.outc)
+				ws.outc = nil
+				w.wg.Add(1)
+				go func() {
+					defer w.wg.Done()
+					w.closingc <- ws
+				}()
+			case <-stopc:
+			}
+		}(w.resuming[i])
+	}
+	go func() {
+		defer close(donec)
+		wg.Wait()
+	}()
+	return donec
+}
+
+// joinSubstreams waits for all substream goroutines to complete.
+func (w *watchGrpcStream) joinSubstreams() {
+	for _, ws := range w.substreams {
+		<-ws.donec
+	}
+	for _, ws := range w.resuming {
+		if ws != nil {
+			<-ws.donec
+		}
+	}
+}
+
+var maxBackoff = 100 * time.Millisecond
+
+// openWatchClient retries opening a watch client until success or halt.
+// manually retry in case "ws==nil && err==nil"
+// TODO: remove FailFast=false
+func (w *watchGrpcStream) openWatchClient() (ws pb.Watch_WatchClient, err error) {
+	backoff := time.Millisecond
+	for {
+		select {
+		case <-w.ctx.Done():
+			if err == nil {
+				return nil, w.ctx.Err()
+			}
+			return nil, err
+		default:
+		}
+		if ws, err = w.remote.Watch(w.ctx, w.callOpts...); ws != nil && err == nil {
+			break
+		}
+		if isHaltErr(w.ctx, err) {
+			return nil, v3rpc.Error(err)
+		}
+		if isUnavailableErr(w.ctx, err) {
+			// retry, but backoff
+			if backoff < maxBackoff {
+				// 25% backoff factor
+				backoff = backoff + backoff/4
+				if backoff > maxBackoff {
+					backoff = maxBackoff
+				}
+			}
+			time.Sleep(backoff)
+		}
+	}
+	return ws, nil
+}
+
+// toPB converts an internal watch request structure to its protobuf WatchRequest structure.
+func (wr *watchRequest) toPB() *pb.WatchRequest {
+	req := &pb.WatchCreateRequest{
+		StartRevision:  wr.rev,
+		Key:            []byte(wr.key),
+		RangeEnd:       []byte(wr.end),
+		ProgressNotify: wr.progressNotify,
+		Filters:        wr.filters,
+		PrevKv:         wr.prevKV,
+		Fragment:       wr.fragment,
+	}
+	cr := &pb.WatchRequest_CreateRequest{CreateRequest: req}
+	return &pb.WatchRequest{RequestUnion: cr}
+}
+
+// toPB converts an internal progress request structure to its protobuf WatchRequest structure.
+func (pr *progressRequest) toPB() *pb.WatchRequest {
+	req := &pb.WatchProgressRequest{}
+	cr := &pb.WatchRequest_ProgressRequest{ProgressRequest: req}
+	return &pb.WatchRequest{RequestUnion: cr}
+}
+
+func streamKeyFromCtx(ctx context.Context) string {
+	if md, ok := metadata.FromOutgoingContext(ctx); ok {
+		return fmt.Sprintf("%+v", md)
+	}
+	return ""
+}