diff --git a/vendor/github.com/coreos/etcd/raft/progress.go b/vendor/github.com/coreos/etcd/raft/progress.go
new file mode 100644
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+++ b/vendor/github.com/coreos/etcd/raft/progress.go
@@ -0,0 +1,284 @@
+// Copyright 2015 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 raft
+
+import "fmt"
+
+const (
+	ProgressStateProbe ProgressStateType = iota
+	ProgressStateReplicate
+	ProgressStateSnapshot
+)
+
+type ProgressStateType uint64
+
+var prstmap = [...]string{
+	"ProgressStateProbe",
+	"ProgressStateReplicate",
+	"ProgressStateSnapshot",
+}
+
+func (st ProgressStateType) String() string { return prstmap[uint64(st)] }
+
+// Progress represents a follower’s progress in the view of the leader. Leader maintains
+// progresses of all followers, and sends entries to the follower based on its progress.
+type Progress struct {
+	Match, Next uint64
+	// State defines how the leader should interact with the follower.
+	//
+	// When in ProgressStateProbe, leader sends at most one replication message
+	// per heartbeat interval. It also probes actual progress of the follower.
+	//
+	// When in ProgressStateReplicate, leader optimistically increases next
+	// to the latest entry sent after sending replication message. This is
+	// an optimized state for fast replicating log entries to the follower.
+	//
+	// When in ProgressStateSnapshot, leader should have sent out snapshot
+	// before and stops sending any replication message.
+	State ProgressStateType
+
+	// Paused is used in ProgressStateProbe.
+	// When Paused is true, raft should pause sending replication message to this peer.
+	Paused bool
+	// PendingSnapshot is used in ProgressStateSnapshot.
+	// If there is a pending snapshot, the pendingSnapshot will be set to the
+	// index of the snapshot. If pendingSnapshot is set, the replication process of
+	// this Progress will be paused. raft will not resend snapshot until the pending one
+	// is reported to be failed.
+	PendingSnapshot uint64
+
+	// RecentActive is true if the progress is recently active. Receiving any messages
+	// from the corresponding follower indicates the progress is active.
+	// RecentActive can be reset to false after an election timeout.
+	RecentActive bool
+
+	// inflights is a sliding window for the inflight messages.
+	// Each inflight message contains one or more log entries.
+	// The max number of entries per message is defined in raft config as MaxSizePerMsg.
+	// Thus inflight effectively limits both the number of inflight messages
+	// and the bandwidth each Progress can use.
+	// When inflights is full, no more message should be sent.
+	// When a leader sends out a message, the index of the last
+	// entry should be added to inflights. The index MUST be added
+	// into inflights in order.
+	// When a leader receives a reply, the previous inflights should
+	// be freed by calling inflights.freeTo with the index of the last
+	// received entry.
+	ins *inflights
+
+	// IsLearner is true if this progress is tracked for a learner.
+	IsLearner bool
+}
+
+func (pr *Progress) resetState(state ProgressStateType) {
+	pr.Paused = false
+	pr.PendingSnapshot = 0
+	pr.State = state
+	pr.ins.reset()
+}
+
+func (pr *Progress) becomeProbe() {
+	// If the original state is ProgressStateSnapshot, progress knows that
+	// the pending snapshot has been sent to this peer successfully, then
+	// probes from pendingSnapshot + 1.
+	if pr.State == ProgressStateSnapshot {
+		pendingSnapshot := pr.PendingSnapshot
+		pr.resetState(ProgressStateProbe)
+		pr.Next = max(pr.Match+1, pendingSnapshot+1)
+	} else {
+		pr.resetState(ProgressStateProbe)
+		pr.Next = pr.Match + 1
+	}
+}
+
+func (pr *Progress) becomeReplicate() {
+	pr.resetState(ProgressStateReplicate)
+	pr.Next = pr.Match + 1
+}
+
+func (pr *Progress) becomeSnapshot(snapshoti uint64) {
+	pr.resetState(ProgressStateSnapshot)
+	pr.PendingSnapshot = snapshoti
+}
+
+// maybeUpdate returns false if the given n index comes from an outdated message.
+// Otherwise it updates the progress and returns true.
+func (pr *Progress) maybeUpdate(n uint64) bool {
+	var updated bool
+	if pr.Match < n {
+		pr.Match = n
+		updated = true
+		pr.resume()
+	}
+	if pr.Next < n+1 {
+		pr.Next = n + 1
+	}
+	return updated
+}
+
+func (pr *Progress) optimisticUpdate(n uint64) { pr.Next = n + 1 }
+
+// maybeDecrTo returns false if the given to index comes from an out of order message.
+// Otherwise it decreases the progress next index to min(rejected, last) and returns true.
+func (pr *Progress) maybeDecrTo(rejected, last uint64) bool {
+	if pr.State == ProgressStateReplicate {
+		// the rejection must be stale if the progress has matched and "rejected"
+		// is smaller than "match".
+		if rejected <= pr.Match {
+			return false
+		}
+		// directly decrease next to match + 1
+		pr.Next = pr.Match + 1
+		return true
+	}
+
+	// the rejection must be stale if "rejected" does not match next - 1
+	if pr.Next-1 != rejected {
+		return false
+	}
+
+	if pr.Next = min(rejected, last+1); pr.Next < 1 {
+		pr.Next = 1
+	}
+	pr.resume()
+	return true
+}
+
+func (pr *Progress) pause()  { pr.Paused = true }
+func (pr *Progress) resume() { pr.Paused = false }
+
+// IsPaused returns whether sending log entries to this node has been
+// paused. A node may be paused because it has rejected recent
+// MsgApps, is currently waiting for a snapshot, or has reached the
+// MaxInflightMsgs limit.
+func (pr *Progress) IsPaused() bool {
+	switch pr.State {
+	case ProgressStateProbe:
+		return pr.Paused
+	case ProgressStateReplicate:
+		return pr.ins.full()
+	case ProgressStateSnapshot:
+		return true
+	default:
+		panic("unexpected state")
+	}
+}
+
+func (pr *Progress) snapshotFailure() { pr.PendingSnapshot = 0 }
+
+// needSnapshotAbort returns true if snapshot progress's Match
+// is equal or higher than the pendingSnapshot.
+func (pr *Progress) needSnapshotAbort() bool {
+	return pr.State == ProgressStateSnapshot && pr.Match >= pr.PendingSnapshot
+}
+
+func (pr *Progress) String() string {
+	return fmt.Sprintf("next = %d, match = %d, state = %s, waiting = %v, pendingSnapshot = %d", pr.Next, pr.Match, pr.State, pr.IsPaused(), pr.PendingSnapshot)
+}
+
+type inflights struct {
+	// the starting index in the buffer
+	start int
+	// number of inflights in the buffer
+	count int
+
+	// the size of the buffer
+	size int
+
+	// buffer contains the index of the last entry
+	// inside one message.
+	buffer []uint64
+}
+
+func newInflights(size int) *inflights {
+	return &inflights{
+		size: size,
+	}
+}
+
+// add adds an inflight into inflights
+func (in *inflights) add(inflight uint64) {
+	if in.full() {
+		panic("cannot add into a full inflights")
+	}
+	next := in.start + in.count
+	size := in.size
+	if next >= size {
+		next -= size
+	}
+	if next >= len(in.buffer) {
+		in.growBuf()
+	}
+	in.buffer[next] = inflight
+	in.count++
+}
+
+// grow the inflight buffer by doubling up to inflights.size. We grow on demand
+// instead of preallocating to inflights.size to handle systems which have
+// thousands of Raft groups per process.
+func (in *inflights) growBuf() {
+	newSize := len(in.buffer) * 2
+	if newSize == 0 {
+		newSize = 1
+	} else if newSize > in.size {
+		newSize = in.size
+	}
+	newBuffer := make([]uint64, newSize)
+	copy(newBuffer, in.buffer)
+	in.buffer = newBuffer
+}
+
+// freeTo frees the inflights smaller or equal to the given `to` flight.
+func (in *inflights) freeTo(to uint64) {
+	if in.count == 0 || to < in.buffer[in.start] {
+		// out of the left side of the window
+		return
+	}
+
+	idx := in.start
+	var i int
+	for i = 0; i < in.count; i++ {
+		if to < in.buffer[idx] { // found the first large inflight
+			break
+		}
+
+		// increase index and maybe rotate
+		size := in.size
+		if idx++; idx >= size {
+			idx -= size
+		}
+	}
+	// free i inflights and set new start index
+	in.count -= i
+	in.start = idx
+	if in.count == 0 {
+		// inflights is empty, reset the start index so that we don't grow the
+		// buffer unnecessarily.
+		in.start = 0
+	}
+}
+
+func (in *inflights) freeFirstOne() { in.freeTo(in.buffer[in.start]) }
+
+// full returns true if the inflights is full.
+func (in *inflights) full() bool {
+	return in.count == in.size
+}
+
+// resets frees all inflights.
+func (in *inflights) reset() {
+	in.count = 0
+	in.start = 0
+}