New metric indicating whether Jenkins is in quietdown mode

This metric exposes the Jenkins isQuietingDown status as a gauge.
When Jenkins is in quiet mode, the new metric will represent this
as a '1', otherwise the value will be '0'

Exposing this metric allows Prometheus to determine whether Jenkins
is in quiet mode.  This can be useful in cases where an alert should
be triggered if quiet mode has been enabled for too long or falls
outside of a maintenance window.

Fixes issue jenkinsci#686

docs/metrics/index.md

@@ -40,6 +40,7 @@ Required Plugin:
 | default_jenkins_up           | Shows if jenkins ready to receive requests | gauge           |
 | default_jenkins_uptime       | Shows time since Jenkins was initialized   | gauge           |
 | default_jenkins_nodes_online | Shows Nodes online status                  | gauge           |
+| default_jenkins_quietdown    | Shows if jenkins is in quiet mode          | gauge           |
 
 ## JobCollector
 

src/main/java/org/jenkinsci/plugins/prometheus/JenkinsStatusCollector.java

@@ -23,6 +23,7 @@ public List<MetricFamilySamples> collect() {
         collectors.add(factory.createJenkinsCollector(CollectorType.JENKINS_UP_GAUGE, new String[]{}));
         collectors.add(factory.createJenkinsCollector(CollectorType.JENKINS_UPTIME_GAUGE, new String[]{}));
         collectors.add(factory.createJenkinsCollector(CollectorType.NODES_ONLINE_GAUGE, new String[]{"node"}));
+        collectors.add(factory.createJenkinsCollector(CollectorType.JENKINS_QUIETDOWN_GAUGE, new String[]{}));
 
         collectors.forEach(c -> c.calculateMetric(jenkins, new String[]{}));
 

src/main/java/org/jenkinsci/plugins/prometheus/collectors/CollectorType.java

@@ -5,6 +5,7 @@ public enum CollectorType {
     JENKINS_UP_GAUGE("up"),
     JENKINS_UPTIME_GAUGE("uptime"),
     JENKINS_VERSION_INFO_GAUGE("version"),
+    JENKINS_QUIETDOWN_GAUGE("quietdown"),
     NODES_ONLINE_GAUGE("nodes_online"),
     BUILD_DURATION_GAUGE("build_duration_milliseconds"),
     BUILD_LOGFILE_SIZE_GAUGE("build_logfile_size_bytes"),

src/main/java/org/jenkinsci/plugins/prometheus/collectors/jenkins/JenkinsCollectorFactory.java

@@ -17,6 +17,8 @@ public class JenkinsCollectorFactory extends BaseCollectorFactory {
         switch (type) {
             case JENKINS_UP_GAUGE:
                 return saveBuildCollector(new JenkinsUpGauge(labelNames, namespace, subsystem));
+            case JENKINS_QUIETDOWN_GAUGE:
+                return saveBuildCollector(new JenkinsQuietDownGauge(labelNames, namespace, subsystem));
             case NODES_ONLINE_GAUGE:
                 if (!isNodeOnlineGaugeEnabled()) {
                     return new NoOpMetricCollector<>();

src/main/java/org/jenkinsci/plugins/prometheus/collectors/jenkins/JenkinsQuietDownGauge.java

@@ -0,0 +1,37 @@
+package org.jenkinsci.plugins.prometheus.collectors.jenkins;
+
+import io.prometheus.client.Gauge;
+import io.prometheus.client.SimpleCollector;
+import jenkins.model.Jenkins;
+import org.jenkinsci.plugins.prometheus.collectors.BaseMetricCollector;
+import org.jenkinsci.plugins.prometheus.collectors.CollectorType;
+
+public class JenkinsQuietDownGauge extends BaseMetricCollector<Jenkins, Gauge> {
+
+    JenkinsQuietDownGauge(String[] labelNames, String namespace, String subsystem) {
+        super(labelNames, namespace, subsystem);
+    }
+
+    @Override
+    protected CollectorType getCollectorType() {
+        return CollectorType.JENKINS_QUIETDOWN_GAUGE;
+    }
+
+    @Override
+    protected String getHelpText() {
+        return "Is Jenkins in quiet mode";
+    }
+
+    @Override
+    protected SimpleCollector.Builder<?, Gauge> getCollectorBuilder() {
+        return Gauge.build();
+    }
+
+    @Override
+    public void calculateMetric(Jenkins jenkinsObject, String[] labelValues) {
+        if (jenkinsObject == null) {
+            return;
+        }
+        this.collector.set(jenkinsObject.isQuietingDown() ? 1 : 0);
+    }
+}

src/test/java/org/jenkinsci/plugins/prometheus/collectors/jenkins/JenkinsQuietDownGaugeTest.java

@@ -0,0 +1,71 @@
+package org.jenkinsci.plugins.prometheus.collectors.jenkins;
+
+import io.prometheus.client.Collector;
+import org.jenkinsci.plugins.prometheus.collectors.testutils.MockedJenkinsTest;
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+
+import static org.mockito.Mockito.when;
+
+public class JenkinsQuietDownGaugeTest extends MockedJenkinsTest {
+
+
+    @Test
+    public void testCollectResultForJenkinsQuietModeEnabled() {
+
+        when(mock.isQuietingDown()).thenReturn(true);
+
+        JenkinsQuietDownGauge sut = new JenkinsQuietDownGauge(new String[]{}, getNamespace(), getSubSystem());
+        sut.calculateMetric(mock, getLabelValues());
+
+        List<Collector.MetricFamilySamples> collect = sut.collect();
+
+        validateMetricFamilySampleListSize(collect, 1);
+
+        Collector.MetricFamilySamples samples = collect.get(0);
+
+        validateNames(samples, new String[]{"default_jenkins_quietdown"});
+        validateMetricFamilySampleSize(samples, 1);
+        validateHelp(samples, "Is Jenkins in quiet mode");
+        validateValue(samples, 0, 1.0);
+    }
+
+
+    @Test
+    public void testCollectResultForJenkinsQuietModeDisabled() {
+
+        when(mock.isQuietingDown()).thenReturn(false);
+
+        JenkinsQuietDownGauge sut = new JenkinsQuietDownGauge(new String[]{}, getNamespace(), getSubSystem());
+        sut.calculateMetric(mock, getLabelValues());
+
+        List<Collector.MetricFamilySamples> collect = sut.collect();
+
+        validateMetricFamilySampleListSize(collect, 1);
+
+        Collector.MetricFamilySamples samples = collect.get(0);
+
+        validateNames(samples, new String[]{"default_jenkins_quietdown"});
+        validateMetricFamilySampleSize(samples, 1);
+        validateHelp(samples, "Is Jenkins in quiet mode");
+        validateValue(samples, 0, 0.0);
+    }
+
+    @Test
+    public void testJenkinsIsNull() {
+        JenkinsQuietDownGauge sut = new JenkinsQuietDownGauge(new String[]{}, getNamespace(), getSubSystem());
+        sut.calculateMetric(null, getLabelValues());
+
+        List<Collector.MetricFamilySamples> collect = sut.collect();
+
+        validateMetricFamilySampleListSize(collect, 1);
+
+        Collector.MetricFamilySamples samples = collect.get(0);
+
+        validateNames(samples, new String[]{"default_jenkins_quietdown"});
+        validateMetricFamilySampleSize(samples, 1);
+        validateHelp(samples, "Is Jenkins in quiet mode");
+        validateValue(samples, 0, 0.0);
+    }
+}