Added docker container State.Health.Status as a metric prometheus-net#7

Author: Cobertos

ContainerTracker.cs

@@ -122,6 +122,13 @@ private void UpdateStateMetrics(ContainerTrackerStateMetrics metrics, ContainerI
             else
                 metrics.RunningState.Set(0);
 
+            if (container.State.Status == "healthy")
+                metrics.HealthState.Set(1);
+            else if (container.State.Status == "starting")
+                metrics.HealthState.Set(0.5);
+            else // "unhealthy"
+                metrics.HealthState.Set(0);
+
             if (container.State.Running && !string.IsNullOrWhiteSpace(container.State.StartedAt))
                 metrics.StartTime.SetToTimeUtc(DateTimeOffset.Parse(container.State.StartedAt));
         }

ContainerTrackerStateMetrics.cs

@@ -7,26 +7,30 @@ sealed class ContainerTrackerStateMetrics : IDisposable
     {
         public Gauge.Child RestartCount { get; private set; }
         public Gauge.Child RunningState { get; private set; }
+        public Gauge.Child HealthState { get; private set; }
         public Gauge.Child StartTime { get; private set; }
 
         public ContainerTrackerStateMetrics(string displayName)
         {
             RestartCount = BaseRestartCount.WithLabels(displayName);
             RunningState = BaseRunningState.WithLabels(displayName);
+            HealthState = BaseHealthState.WithLabels(displayName);
             StartTime = BaseStartTime.WithLabels(displayName);
         }
 
         public void Dispose()
         {
             RestartCount.Remove();
             RunningState.Remove();
+            HealthState.Remove();
             StartTime.Remove();
         }
 
         public void Unpublish()
         {
             RestartCount.Unpublish();
             RunningState.Unpublish();
+            HealthState.Unpublish();
             StartTime.Unpublish();
         }
 
@@ -36,6 +40,9 @@ public void Unpublish()
         private static readonly Gauge BaseRunningState = Metrics
             .CreateGauge("docker_container_running_state", "Whether the container is running (1), restarting (0.5) or stopped (0).", ConfigureGauge());
 
+        private static readonly Gauge BaseHealthState = Metrics
+            .CreateGauge("docker_container_health_state", "Whether the container is healthy (1), starting (0.5) or unhealthy (0).", ConfigureGauge());
+
         private static readonly Gauge BaseStartTime = Metrics
             .CreateGauge("docker_container_start_time_seconds", "Timestamp indicating when the container was started. Does not get reset by automatic restarts.", ConfigureGauge());