diff --git a/vendor/github.com/hashicorp/serf/coordinate/client.go b/vendor/github.com/hashicorp/serf/coordinate/client.go
new file mode 100644
index 0000000..3582ee4
--- /dev/null
+++ b/vendor/github.com/hashicorp/serf/coordinate/client.go
@@ -0,0 +1,243 @@
+package coordinate
+
+import (
+	"fmt"
+	"math"
+	"sort"
+	"sync"
+	"time"
+
+	"github.com/armon/go-metrics"
+)
+
+// Client manages the estimated network coordinate for a given node, and adjusts
+// it as the node observes round trip times and estimated coordinates from other
+// nodes. The core algorithm is based on Vivaldi, see the documentation for Config
+// for more details.
+type Client struct {
+	// coord is the current estimate of the client's network coordinate.
+	coord *Coordinate
+
+	// origin is a coordinate sitting at the origin.
+	origin *Coordinate
+
+	// config contains the tuning parameters that govern the performance of
+	// the algorithm.
+	config *Config
+
+	// adjustmentIndex is the current index into the adjustmentSamples slice.
+	adjustmentIndex uint
+
+	// adjustment is used to store samples for the adjustment calculation.
+	adjustmentSamples []float64
+
+	// latencyFilterSamples is used to store the last several RTT samples,
+	// keyed by node name. We will use the config's LatencyFilterSamples
+	// value to determine how many samples we keep, per node.
+	latencyFilterSamples map[string][]float64
+
+	// stats is used to record events that occur when updating coordinates.
+	stats ClientStats
+
+	// mutex enables safe concurrent access to the client.
+	mutex sync.RWMutex
+}
+
+// ClientStats is used to record events that occur when updating coordinates.
+type ClientStats struct {
+	// Resets is incremented any time we reset our local coordinate because
+	// our calculations have resulted in an invalid state.
+	Resets int
+}
+
+// NewClient creates a new Client and verifies the configuration is valid.
+func NewClient(config *Config) (*Client, error) {
+	if !(config.Dimensionality > 0) {
+		return nil, fmt.Errorf("dimensionality must be >0")
+	}
+
+	return &Client{
+		coord:                NewCoordinate(config),
+		origin:               NewCoordinate(config),
+		config:               config,
+		adjustmentIndex:      0,
+		adjustmentSamples:    make([]float64, config.AdjustmentWindowSize),
+		latencyFilterSamples: make(map[string][]float64),
+	}, nil
+}
+
+// GetCoordinate returns a copy of the coordinate for this client.
+func (c *Client) GetCoordinate() *Coordinate {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+
+	return c.coord.Clone()
+}
+
+// SetCoordinate forces the client's coordinate to a known state.
+func (c *Client) SetCoordinate(coord *Coordinate) error {
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+
+	if err := c.checkCoordinate(coord); err != nil {
+		return err
+	}
+
+	c.coord = coord.Clone()
+	return nil
+}
+
+// ForgetNode removes any client state for the given node.
+func (c *Client) ForgetNode(node string) {
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+
+	delete(c.latencyFilterSamples, node)
+}
+
+// Stats returns a copy of stats for the client.
+func (c *Client) Stats() ClientStats {
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+
+	return c.stats
+}
+
+// checkCoordinate returns an error if the coordinate isn't compatible with
+// this client, or if the coordinate itself isn't valid. This assumes the mutex
+// has been locked already.
+func (c *Client) checkCoordinate(coord *Coordinate) error {
+	if !c.coord.IsCompatibleWith(coord) {
+		return fmt.Errorf("dimensions aren't compatible")
+	}
+
+	if !coord.IsValid() {
+		return fmt.Errorf("coordinate is invalid")
+	}
+
+	return nil
+}
+
+// latencyFilter applies a simple moving median filter with a new sample for
+// a node. This assumes that the mutex has been locked already.
+func (c *Client) latencyFilter(node string, rttSeconds float64) float64 {
+	samples, ok := c.latencyFilterSamples[node]
+	if !ok {
+		samples = make([]float64, 0, c.config.LatencyFilterSize)
+	}
+
+	// Add the new sample and trim the list, if needed.
+	samples = append(samples, rttSeconds)
+	if len(samples) > int(c.config.LatencyFilterSize) {
+		samples = samples[1:]
+	}
+	c.latencyFilterSamples[node] = samples
+
+	// Sort a copy of the samples and return the median.
+	sorted := make([]float64, len(samples))
+	copy(sorted, samples)
+	sort.Float64s(sorted)
+	return sorted[len(sorted)/2]
+}
+
+// updateVivialdi updates the Vivaldi portion of the client's coordinate. This
+// assumes that the mutex has been locked already.
+func (c *Client) updateVivaldi(other *Coordinate, rttSeconds float64) {
+	const zeroThreshold = 1.0e-6
+
+	dist := c.coord.DistanceTo(other).Seconds()
+	if rttSeconds < zeroThreshold {
+		rttSeconds = zeroThreshold
+	}
+	wrongness := math.Abs(dist-rttSeconds) / rttSeconds
+
+	totalError := c.coord.Error + other.Error
+	if totalError < zeroThreshold {
+		totalError = zeroThreshold
+	}
+	weight := c.coord.Error / totalError
+
+	c.coord.Error = c.config.VivaldiCE*weight*wrongness + c.coord.Error*(1.0-c.config.VivaldiCE*weight)
+	if c.coord.Error > c.config.VivaldiErrorMax {
+		c.coord.Error = c.config.VivaldiErrorMax
+	}
+
+	delta := c.config.VivaldiCC * weight
+	force := delta * (rttSeconds - dist)
+	c.coord = c.coord.ApplyForce(c.config, force, other)
+}
+
+// updateAdjustment updates the adjustment portion of the client's coordinate, if
+// the feature is enabled. This assumes that the mutex has been locked already.
+func (c *Client) updateAdjustment(other *Coordinate, rttSeconds float64) {
+	if c.config.AdjustmentWindowSize == 0 {
+		return
+	}
+
+	// Note that the existing adjustment factors don't figure in to this
+	// calculation so we use the raw distance here.
+	dist := c.coord.rawDistanceTo(other)
+	c.adjustmentSamples[c.adjustmentIndex] = rttSeconds - dist
+	c.adjustmentIndex = (c.adjustmentIndex + 1) % c.config.AdjustmentWindowSize
+
+	sum := 0.0
+	for _, sample := range c.adjustmentSamples {
+		sum += sample
+	}
+	c.coord.Adjustment = sum / (2.0 * float64(c.config.AdjustmentWindowSize))
+}
+
+// updateGravity applies a small amount of gravity to pull coordinates towards
+// the center of the coordinate system to combat drift. This assumes that the
+// mutex is locked already.
+func (c *Client) updateGravity() {
+	dist := c.origin.DistanceTo(c.coord).Seconds()
+	force := -1.0 * math.Pow(dist/c.config.GravityRho, 2.0)
+	c.coord = c.coord.ApplyForce(c.config, force, c.origin)
+}
+
+// Update takes other, a coordinate for another node, and rtt, a round trip
+// time observation for a ping to that node, and updates the estimated position of
+// the client's coordinate. Returns the updated coordinate.
+func (c *Client) Update(node string, other *Coordinate, rtt time.Duration) (*Coordinate, error) {
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+
+	if err := c.checkCoordinate(other); err != nil {
+		return nil, err
+	}
+
+	// The code down below can handle zero RTTs, which we have seen in
+	// https://github.com/hashicorp/consul/issues/3789, presumably in
+	// environments with coarse-grained monotonic clocks (we are still
+	// trying to pin this down). In any event, this is ok from a code PoV
+	// so we don't need to alert operators with spammy messages. We did
+	// add a counter so this is still observable, though.
+	const maxRTT = 10 * time.Second
+	if rtt < 0 || rtt > maxRTT {
+		return nil, fmt.Errorf("round trip time not in valid range, duration %v is not a positive value less than %v ", rtt, maxRTT)
+	}
+	if rtt == 0 {
+		metrics.IncrCounter([]string{"serf", "coordinate", "zero-rtt"}, 1)
+	}
+
+	rttSeconds := c.latencyFilter(node, rtt.Seconds())
+	c.updateVivaldi(other, rttSeconds)
+	c.updateAdjustment(other, rttSeconds)
+	c.updateGravity()
+	if !c.coord.IsValid() {
+		c.stats.Resets++
+		c.coord = NewCoordinate(c.config)
+	}
+
+	return c.coord.Clone(), nil
+}
+
+// DistanceTo returns the estimated RTT from the client's coordinate to other, the
+// coordinate for another node.
+func (c *Client) DistanceTo(other *Coordinate) time.Duration {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+
+	return c.coord.DistanceTo(other)
+}