Add Server count metric

e2e/metrics_assertions_test.go

@@ -138,3 +138,29 @@ func assertAgentKnownServerCount(expectedServerCount int) func(context.Context,
 		return ctx
 	}
 }
+
+// assertServerCountMetric asserts that the server count metric is set to the expected value.
+func assertServerCountMetric(expectedServerCount int) func(context.Context, *testing.T, *envconf.Config) context.Context {
+	return func(ctx context.Context, t *testing.T, cfg *envconf.Config) context.Context {
+		client := cfg.Client()
+
+		serverPods := &corev1.PodList{}
+		err := client.Resources().List(ctx, serverPods, resources.WithLabelSelector("k8s-app=konnectivity-server"))
+		if err != nil {
+			t.Fatalf("couldn't get server pods (label selector 'k8s-app=konnectivity-server'): %v", err)
+		}
+
+		for _, serverPod := range serverPods.Items {
+			serverCount, err := getMetricsGaugeValue(cfg.Client().RESTConfig(), serverPod.Namespace, serverPod.Name, 8095, "konnectivity_network_proxy_server_server_count")
+			if err != nil {
+				t.Fatalf("couldn't get server metric 'konnectivity_network_proxy_server_server_count' for pod %v: %v", serverPod.Name, err)
+			}
+
+			if serverCount != expectedServerCount {
+				t.Errorf("incorrect server count metric (want: %v, got: %v)", expectedServerCount, serverCount)
+			}
+		}
+
+		return ctx
+	}
+}

e2e/static_count_test.go

@@ -92,6 +92,7 @@ func TestSingleServer_SingleAgent_StaticCount(t *testing.T) {
 	feature = feature.Assess("konnectivity server has a connected client", assertServersAreConnected(1))
 	feature = feature.Assess("konnectivity agent is connected to a server", assertAgentsAreConnected(1))
 	feature = feature.Assess("agents correctly count 1 server", assertAgentKnownServerCount(1))
+	feature = feature.Assess("server count metric is set correctly", assertServerCountMetric(1))
 	feature = feature.Teardown(deleteDeployment(agentDeployment))
 	feature = feature.Teardown(deleteDeployment(serverDeployment))
 
@@ -113,6 +114,7 @@ func TestMultiServer_MultiAgent_StaticCount(t *testing.T) {
 	feature = feature.Assess("all servers connected to all clients", assertServersAreConnected(replicas))
 	feature = feature.Assess("all agents connected to all servers", assertAgentsAreConnected(replicas))
 	feature = feature.Assess("agents correctly count all servers", assertAgentKnownServerCount(replicas))
+	feature = feature.Assess("server count metric is set correctly", assertServerCountMetric(replicas))
 	feature = feature.Teardown(deleteDeployment(agentDeployment))
 	feature = feature.Teardown(deleteDeployment(serverDeployment))
 

pkg/server/metrics/metrics.go

@@ -64,6 +64,7 @@ type ServerMetrics struct {
 	leaseDeletes         *prometheus.CounterVec
 	leaseListLatencies   *prometheus.HistogramVec
 	leaseLists           *prometheus.CounterVec
+	serverCount          prometheus.Gauge
 }
 
 // newServerMetrics create a new ServerMetrics, configured with default metric names.
@@ -209,6 +210,14 @@ func newServerMetrics() *ServerMetrics {
 		},
 		[]string{"http_status_code", "reason"},
 	)
+	serverCount := prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Namespace: Namespace,
+			Subsystem: Subsystem,
+			Name:      "server_count",
+			Help:      "Number of proxy server instances in the cluster",
+		},
+	)
 	streamPackets := commonmetrics.MakeStreamPacketsTotalMetric(Namespace, Subsystem)
 	streamErrors := commonmetrics.MakeStreamErrorsTotalMetric(Namespace, Subsystem)
 	prometheus.MustRegister(endpointLatencies)
@@ -228,6 +237,7 @@ func newServerMetrics() *ServerMetrics {
 	prometheus.MustRegister(leaseDeletes)
 	prometheus.MustRegister(leaseListLatencies)
 	prometheus.MustRegister(leaseLists)
+	prometheus.MustRegister(serverCount)
 	return &ServerMetrics{
 		endpointLatencies:    endpointLatencies,
 		frontendLatencies:    frontendLatencies,
@@ -246,6 +256,7 @@ func newServerMetrics() *ServerMetrics {
 		leaseDeletes:         leaseDeletes,
 		leaseListLatencies:   leaseListLatencies,
 		leaseLists:           leaseLists,
+		serverCount:          serverCount,
 	}
 }
 
@@ -315,6 +326,11 @@ func (s *ServerMetrics) SetEstablishedConnCount(count int) {
 	s.establishedConns.WithLabelValues().Set(float64(count))
 }
 
+// SetServerCount sets the number of proxy server instances in the cluster.
+func (s *ServerMetrics) SetServerCount(count int) {
+	s.serverCount.Set(float64(count))
+}
+
 // FullRecvChannel retrieves the metric for counting full receive channels.
 func (s *ServerMetrics) FullRecvChannel(serviceMethod string) prometheus.Gauge {
 	return s.fullRecvChannels.With(prometheus.Labels{"service_method": serviceMethod})

pkg/server/metrics/metrics_test.go

@@ -0,0 +1,62 @@
+/*
+Copyright 2024 The Kubernetes 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 metrics
+
+import (
+	"testing"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/testutil"
+)
+
+// TestServerCountMetric tests the server count metric.
+func TestServerCountMetric(t *testing.T) {
+	// Reset metrics to ensure clean state
+	Metrics.Reset()
+
+	// Test setting server count
+	expectedCount := 3
+	Metrics.SetServerCount(expectedCount)
+
+	// Verify the metric value
+	actualCount := testutil.ToFloat64(Metrics.serverCount)
+	if actualCount != float64(expectedCount) {
+		t.Errorf("Expected server count %d, got %f", expectedCount, actualCount)
+	}
+
+	// Test updating server count
+	newCount := 5
+	Metrics.SetServerCount(newCount)
+	actualCount = testutil.ToFloat64(Metrics.serverCount)
+	if actualCount != float64(newCount) {
+		t.Errorf("Expected updated server count %d, got %f", newCount, actualCount)
+	}
+}
+
+// TestServerCountMetricRegistration tests the registration of the server count metric.
+func TestServerCountMetricRegistration(t *testing.T) {
+	// Verify the metric is properly registered
+	registry := prometheus.NewRegistry()
+	registry.MustRegister(Metrics.serverCount)
+
+	// Set a value and check if it's accessible
+	Metrics.SetServerCount(2)
+	actualCount := testutil.ToFloat64(Metrics.serverCount)
+	if actualCount != 2.0 {
+		t.Errorf("Expected server count 2, got %f", actualCount)
+	}
+}

pkg/server/server.go

@@ -389,6 +389,8 @@ func NewProxyServer(serverID string, proxyStrategies []proxystrategies.ProxyStra
 		}
 	}
 
+	metrics.Metrics.SetServerCount(serverCount)
+
 	return &ProxyServer{
 		established:                make(map[string](map[int64]*ProxyClientConnection)),
 		PendingDial:                NewPendingDialManager(),