Prevent leaking collectors when HPA gets updated (#54)

* Prevent leaking collectors when HPA gets updated

This fixes an issue where collectors would be leaking when HPAs are
getting updated.

Fix this by stopping the collector started for the previous version of
the HPA.

Signed-off-by: Mikkel Oscar Lyderik Larsen <mikkel.larsen@zalando.de>

* Add tests to verify old collector is removed

Signed-off-by: Mikkel Oscar Lyderik Larsen <mikkel.larsen@zalando.de>

pkg/provider/hpa_test.go

@@ -0,0 +1,95 @@
+package provider
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+	"github.com/zalando-incubator/kube-metrics-adapter/pkg/collector"
+	autoscalingv2 "k8s.io/api/autoscaling/v2beta2"
+	"k8s.io/apimachinery/pkg/api/resource"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/client-go/kubernetes/fake"
+)
+
+type mockCollectorPlugin struct{}
+
+func (m mockCollectorPlugin) NewCollector(hpa *autoscalingv2.HorizontalPodAutoscaler, config *collector.MetricConfig, interval time.Duration) (collector.Collector, error) {
+	return mockCollector{}, nil
+}
+
+type mockCollector struct{}
+
+func (c mockCollector) GetMetrics() ([]collector.CollectedMetric, error) {
+	return nil, nil
+}
+
+func (c mockCollector) Interval() time.Duration {
+	return 1 * time.Second
+}
+
+func TestUpdateHPAs(t *testing.T) {
+	value := resource.MustParse("1k")
+	hpa := &autoscalingv2.HorizontalPodAutoscaler{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      "hpa1",
+			Namespace: "default",
+			Annotations: map[string]string{
+				"metric-config.pods.requests-per-second.json-path/json-key": "$.http_server.rps",
+				"metric-config.pods.requests-per-second.json-path/path":     "/metrics",
+				"metric-config.pods.requests-per-second.json-path/port":     "9090",
+			},
+		},
+		Spec: autoscalingv2.HorizontalPodAutoscalerSpec{
+			ScaleTargetRef: autoscalingv2.CrossVersionObjectReference{
+				Kind:       "Deployment",
+				Name:       "app",
+				APIVersion: "apps/v1",
+			},
+			MinReplicas: &[]int32{1}[0],
+			MaxReplicas: 10,
+			Metrics: []autoscalingv2.MetricSpec{
+				{
+					Type: autoscalingv2.PodsMetricSourceType,
+					Pods: &autoscalingv2.PodsMetricSource{
+						Metric: autoscalingv2.MetricIdentifier{
+							Name: "requests-per-second",
+						},
+						Target: autoscalingv2.MetricTarget{
+							Type:         autoscalingv2.AverageValueMetricType,
+							AverageValue: &value,
+						},
+					},
+				},
+			},
+		},
+	}
+
+	fakeClient := fake.NewSimpleClientset()
+
+	var err error
+	hpa, err = fakeClient.AutoscalingV2beta2().HorizontalPodAutoscalers("default").Create(hpa)
+	require.NoError(t, err)
+
+	collectorFactory := collector.NewCollectorFactory()
+	err = collectorFactory.RegisterPodsCollector("", mockCollectorPlugin{})
+	require.NoError(t, err)
+
+	provider := NewHPAProvider(fakeClient, 1*time.Second, 1*time.Second, collectorFactory)
+	provider.collectorScheduler = NewCollectorScheduler(context.Background(), provider.metricSink)
+
+	err = provider.updateHPAs()
+	require.NoError(t, err)
+	require.Len(t, provider.collectorScheduler.table, 1)
+
+	// update HPA
+	hpa.Annotations["metric-config.pods.requests-per-second.json-path/port"] = "8080"
+	_, err = fakeClient.AutoscalingV2beta2().HorizontalPodAutoscalers("default").Update(hpa)
+	require.NoError(t, err)
+
+	err = provider.updateHPAs()
+	require.NoError(t, err)
+
+	require.Len(t, provider.collectorScheduler.table, 1)
+}