plugin/metrics: Add a metric to monitor which plugin(s) is(are) enabled (#2700)

* Add a GaugeVec for enabled plugins monitoring.

Signed-off-by: Jiacheng Xu <xjcmaxwellcjx@gmail.com>

* Add server label and zone label for enable_plugin matric.

* Add a test for PluginEnabled metric

* Add description for enabledPlugin metric.

* Change the description for the enabledPlugin metric.

* Reset the enabledPlugin metric when restart the server.

* Add the bug session for enabledPlugin metric.

* Remove the resolveTCPAddr

1 files changed, 36 insertions, 0 deletions

diff --git a/test/metrics_test.go b/test/metrics_test.go
index c37126a74..4aaf89036 100644
--- a/test/metrics_test.go
+++ b/test/metrics_test.go
@@ -186,3 +186,39 @@ google.com:0 {
 		t.Errorf("Expected metric data retrieved for %s, expected %d, got %d", cacheSizeMetricName, 1, endCacheSize-beginCacheSize)
 	}
 }
+
+func TestMetricsPluginEnabled(t *testing.T) {
+	corefile := `example.org:0 {
+	chaos CoreDNS-001 miek@miek.nl
+	prometheus localhost:0
+}
+
+example.com:0 {
+	forward . 8.8.4.4:53
+	prometheus localhost:0
+}
+`
+	srv, err := CoreDNSServer(corefile)
+	if err != nil {
+		t.Fatalf("Could not get CoreDNS serving instance: %s", err)
+	}
+	defer srv.Stop()
+
+	metricName := "coredns_plugin_enabled" //{server, zone, name}
+
+	data := test.Scrape("http://" + metrics.ListenAddr + "/metrics")
+
+	// Get the value for the metrics where the one of the labels values matches "chaos".
+	got, _ := test.MetricValueLabel(metricName, "chaos", data)
+
+	if got != "1" {
+		t.Errorf("Expected value %s for %s, but got %s", "1", metricName, got)
+	}
+
+	// Get the value for the metrics where the one of the labels values matches "whoami".
+	got, _ = test.MetricValueLabel(metricName, "whoami", data)
+
+	if got != "" {
+		t.Errorf("Expected value %s for %s, but got %s", "", metricName, got)
+	}
+}