watch pods instead of polling

deployment/roles.yaml

@@ -4,7 +4,7 @@ metadata:
   name: cart-discovery
 rules:
   - apiGroups: [""] # "" indicates the core API group
-    resources: ["pods","services"]
+    resources: ["pods","services", "deployments"]
     verbs: ["get", "watch", "list"]
 ---
 apiVersion: rbac.authorization.k8s.io/v1

deployment/scaling.yaml

@@ -4,8 +4,9 @@ metadata:
   name: cart-scaler
 spec:
   scaleTargetRef:
+    apiVersion: apps/v1
     kind: Deployment
     name: cart-actor
-  minReplicas: 1
-  maxReplicas: 5
+  minReplicas: 2
+  maxReplicas: 8
   targetCPUUtilizationPercentage: 50

discovery.go

@@ -3,12 +3,17 @@ package main
 import (
 	"context"
 
+	v1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/watch"
 	"k8s.io/client-go/kubernetes"
+	"k8s.io/client-go/tools/cache"
+	toolsWatch "k8s.io/client-go/tools/watch"
 )
 
 type Discovery interface {
 	Discover() ([]string, error)
+	Watch() (<-chan string, error)
 }
 
 type K8sDiscovery struct {
@@ -33,6 +38,32 @@ func (k *K8sDiscovery) DiscoverInNamespace(namespace string) ([]string, error) {
 	return hosts, nil
 }
 
+func (k *K8sDiscovery) Watch() (<-chan string, error) {
+	timeout := int64(30)
+	watcherFn := func(options metav1.ListOptions) (watch.Interface, error) {
+		return k.client.CoreV1().Pods("").Watch(k.ctx, metav1.ListOptions{
+			LabelSelector:  "actor-pool=cart",
+			TimeoutSeconds: &timeout,
+		})
+	}
+	watcher, err := toolsWatch.NewRetryWatcher("1", &cache.ListWatch{WatchFunc: watcherFn})
+	if err != nil {
+		return nil, err
+	}
+	ch := make(chan string)
+	go func() {
+		for event := range watcher.ResultChan() {
+			if event.Type != watch.Added {
+				continue
+			}
+			pod := event.Object.(*v1.Pod)
+
+			ch <- pod.Status.PodIP
+		}
+	}()
+	return ch, nil
+}
+
 func NewK8sDiscovery(client *kubernetes.Clientset) *K8sDiscovery {
 	return &K8sDiscovery{
 		ctx:    context.Background(),

discovery_test.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"testing"
+	"time"
 
 	"k8s.io/client-go/kubernetes"
 	"k8s.io/client-go/tools/clientcmd"
@@ -25,3 +26,24 @@ func TestDiscovery(t *testing.T) {
 		t.Errorf("Expected at least one host, got none")
 	}
 }
+
+func TestWatch(t *testing.T) {
+	config, err := clientcmd.BuildConfigFromFlags("", "/Users/mats/.kube/config")
+	if err != nil {
+		t.Errorf("Error building config: %v", err)
+	}
+	client, err := kubernetes.NewForConfig(config)
+	if err != nil {
+		t.Errorf("Error creating client: %v", err)
+	}
+	d := NewK8sDiscovery(client)
+	ch, err := d.Watch()
+	if err != nil {
+		t.Errorf("Error watching: %v", err)
+	}
+	select {
+	case <-ch:
+	case <-time.After(5 * time.Second):
+		t.Errorf("Timeout waiting for watch")
+	}
+}

packet.go

@@ -54,6 +54,7 @@ func SendPacket(conn io.Writer, messageType uint16, datafn func(w io.Writer) err
 		MessageType: messageType,
 		DataLength:  uint16(len(data)),
 	})
+	packetsSent.Inc()
 	_, err = conn.Write(data)
 	return err
 }

synced-pool.go

@@ -78,20 +78,23 @@ func NewSyncedPool(local *GrainLocalPool, hostname string, d Discovery) (*Synced
 
 	if d != nil {
 		go func() {
-			for range time.Tick(time.Second * 5) {
-				hosts, err := d.Discover()
+			ch, err := d.Watch()
 			if err != nil {
 				log.Printf("Error discovering hosts: %v", err)
+				return
 			}
-				for _, h := range pool.ExcludeKnown(hosts) {
-
-					log.Printf("Discovered host %s", h)
-
+			for host := range ch {
+				if pool.IsKnown(host) {
+					continue
+				}
+				go func(h string) {
+					log.Printf("Discovered host %s, waiting for startup", h)
+					time.Sleep(time.Second)
 					err := pool.AddRemote(h)
 					if err != nil {
 						log.Printf("Error adding remote %s: %v", h, err)
 					}
-				}
+				}(host)
 			}
 		}()
 	} else {
@@ -112,6 +115,15 @@ func NewSyncedPool(local *GrainLocalPool, hostname string, d Discovery) (*Synced
 	return pool, nil
 }
 
+func (p *SyncedPool) IsKnown(host string) bool {
+	for _, r := range p.remotes {
+		if r.Host == host {
+			return true
+		}
+	}
+	return host != p.Hostname
+}
+
 func (p *SyncedPool) ExcludeKnown(hosts []string) []string {
 	ret := make([]string, 0, len(hosts))
 	for _, h := range hosts {
@@ -172,6 +184,14 @@ var (
 		Name: "cart_packet_queue_size",
 		Help: "The total number of packets in the queue",
 	})
+	packetsSent = promauto.NewCounter(prometheus.CounterOpts{
+		Name: "cart_pool_packets_sent_total",
+		Help: "The total number of packets sent",
+	})
+	packetsReceived = promauto.NewCounter(prometheus.CounterOpts{
+		Name: "cart_pool_packets_received_total",
+		Help: "The total number of packets received",
+	})
 )
 
 const (
@@ -216,7 +236,7 @@ func NewPacketQueue(connection net.Conn) *PacketQueue {
 
 				//return
 			}
-			packetQueue.Inc()
+
 			queue.mu.Lock()
 			for i, packet := range queue.Packets {
 				if time.Since(packet.Added) < time.Second*5 {
@@ -231,6 +251,8 @@ func NewPacketQueue(connection net.Conn) *PacketQueue {
 				Data:        data,
 			})
 			queue.mu.Unlock()
+			packetsReceived.Inc()
+			packetQueue.Inc()
 		}
 	}()
 	return queue