pkg/{k8s,mesh}: introduce liveness checks

This commit introduces liveness checks to Kilo. This allows the Kilo
daemons to take nodes with inactive or dead Kilo deamons out of the
topology until they are alive again.

pkg/mesh/mesh.go

@@ -77,6 +77,9 @@ type Node struct {
 	ExternalIP *net.IPNet
 	Key        []byte
 	InternalIP *net.IPNet
+	// LastSeen is a Unix time for the last time
+	// the node confirmed it was live.
+	LastSeen int64
 	// Leader is a suggestion to Kilo that
 	// the node wants to lead its segment.
 	Leader   bool
@@ -87,7 +90,7 @@ type Node struct {
 
 // Ready indicates whether or not the node is ready.
 func (n *Node) Ready() bool {
-	return n != nil && n.ExternalIP != nil && n.Key != nil && n.InternalIP != nil && n.Subnet != nil
+	return n != nil && n.ExternalIP != nil && n.Key != nil && n.InternalIP != nil && n.Subnet != nil && time.Now().Unix()-n.LastSeen < int64(resyncPeriod)*2/int64(time.Second)
 }
 
 // EventType describes what kind of an action an event represents.
@@ -284,6 +287,7 @@ func (m *Mesh) Run() error {
 		case e = <-w:
 			m.sync(e)
 		case <-t.C:
+			m.checkIn()
 			m.applyTopology()
 			t.Reset(resyncPeriod)
 		case <-m.stop:
@@ -332,6 +336,25 @@ func (m *Mesh) sync(e *Event) {
 	}
 }
 
+// checkIn will try to update the local node's LastSeen timestamp
+// in the backend.
+func (m *Mesh) checkIn() {
+	m.mu.Lock()
+	n := m.nodes[m.hostname]
+	m.mu.Unlock()
+	if n == nil {
+		level.Debug(m.logger).Log("msg", "no local node found in backend")
+		return
+	}
+	n.LastSeen = time.Now().Unix()
+	if err := m.Set(m.hostname, n); err != nil {
+		level.Error(m.logger).Log("error", fmt.Sprintf("failed to set local node: %v", err), "node", n)
+		m.errorCounter.WithLabelValues("checkin").Inc()
+		return
+	}
+	level.Debug(m.logger).Log("msg", "successfully checked in local node in backend")
+}
+
 func (m *Mesh) handleLocal(n *Node) {
 	// Allow the external IP to be overridden.
 	if n.ExternalIP == nil {
@@ -340,7 +363,16 @@ func (m *Mesh) handleLocal(n *Node) {
 	// Compare the given node to the calculated local node.
 	// Take leader, location, and subnet from the argument, as these
 	// are not determined by kilo.
-	local := &Node{ExternalIP: n.ExternalIP, Key: m.pub, InternalIP: m.internalIP, Leader: n.Leader, Location: n.Location, Name: m.hostname, Subnet: n.Subnet}
+	local := &Node{
+		ExternalIP: n.ExternalIP,
+		Key:        m.pub,
+		InternalIP: m.internalIP,
+		LastSeen:   time.Now().Unix(),
+		Leader:     n.Leader,
+		Location:   n.Location,
+		Name:       m.hostname,
+		Subnet:     n.Subnet,
+	}
 	if !nodesAreEqual(n, local) {
 		level.Debug(m.logger).Log("msg", "local node differs from backend")
 		if err := m.Set(m.hostname, local); err != nil {
@@ -543,6 +575,7 @@ func nodesAreEqual(a, b *Node) bool {
 	if a == b {
 		return true
 	}
+	// Ignore LastSeen when comparing equality.
 	return ipNetsEqual(a.ExternalIP, b.ExternalIP) && string(a.Key) == string(b.Key) && ipNetsEqual(a.InternalIP, b.InternalIP) && a.Leader == b.Leader && a.Location == b.Location && a.Name == b.Name && subnetsEqual(a.Subnet, b.Subnet)
 }
 

pkg/mesh/mesh_test.go

@@ -17,6 +17,7 @@ package mesh
 import (
 	"net"
 	"testing"
+	"time"
 )
 
 func TestNewAllocator(t *testing.T) {
@@ -133,6 +134,7 @@ func TestReady(t *testing.T) {
 				ExternalIP: externalIP,
 				InternalIP: internalIP,
 				Key:        []byte{},
+				LastSeen:   time.Now().Unix(),
 				Subnet:     &net.IPNet{IP: net.ParseIP("10.2.0.0"), Mask: net.CIDRMask(16, 32)},
 			},
 			ready: true,