Add HorizontalPodAutoscaler from kubernetes

src/main/java/cambio/simulator/entities/patterns/HorizontalPodAutoscalingPolicy.java

@@ -0,0 +1,78 @@
+package cambio.simulator.entities.patterns;
+
+import cambio.simulator.entities.microservice.Microservice;
+import cambio.simulator.export.MultiDataPointReporter;
+import cambio.simulator.misc.TimeUtil;
+import cambio.simulator.parsing.JsonTypeName;
+import desmoj.core.simulator.TimeInstant;
+
+@JsonTypeName("hpa")
+public class HorizontalPodAutoscalingPolicy implements IAutoscalingPolicy {
+
+    // TODO Maybe also include via adapter, upscaling/downscaling behavior not 100% as in Kubernetes, e.g. see HorizontalPodAutoscalerBehavior
+    // https://github.com/kubernetes/kubernetes/blob/master/pkg/apis/autoscaling/types.go#L113
+
+    private transient MultiDataPointReporter reporter = null;
+    private double targetUtilization = 0.8;
+    private int minInstances = 1;
+    private int maxInstances = Integer.MAX_VALUE;
+
+    /**
+     * Minimum time an instance has to run before it can be shutdown by down-scaling.
+     */
+    private double holdTime = 120;
+    private transient TimeInstant lastScaleUp = new TimeInstant(0);
+
+    @Override
+    public void apply(Microservice owner) {
+        //https://github.com/kubernetes/kubernetes/blob/8caeec429ee1d2a9df7b7a41b21c626346b456fb/docs/design/horizontal-pod-autoscaler.md#autoscaling-algorithm
+//        Scale-up can only happen if there was no rescaling within the last 3 minutes. Scale-down will wait for 5 minutes from the last rescaling.
+//        Moreover any scaling will only be made if: avg(CurrentPodsConsumption) / Target drops below 0.9 or increases above 1.1 (10% tolerance)
+
+        if (reporter == null) {
+            reporter = new MultiDataPointReporter(String.format("AS[%s]_", owner.getPlainName()), owner.getModel());
+        }
+
+        TimeInstant presentTime = owner.presentTime();
+        int currentInstanceCount = owner.getInstancesCount();
+        double avg2Target = owner.getAverageRelativeUtilization() / targetUtilization;
+        // Tolerance area
+        if (avg2Target > 0.9 && avg2Target < 1.1) {
+            return;
+        }
+
+        int newInstanceCount = (int) Math.ceil(avg2Target * currentInstanceCount);
+
+        newInstanceCount = Math.min(newInstanceCount, maxInstances);
+        newInstanceCount = Math.max(minInstances, newInstanceCount);
+
+        if (currentInstanceCount < minInstances) { //starts minimum instances
+            owner.setInstancesCount(minInstances);
+            reporter.addDatapoint("Decision", presentTime, "Spawn");
+            reporter.addDatapoint("InstanceChange", presentTime, minInstances-currentInstanceCount);
+        } else if (currentInstanceCount > maxInstances) {
+            owner.setInstancesCount(maxInstances);
+            reporter.addDatapoint("Decision", presentTime, "Despawn");
+            reporter.addDatapoint("InstanceChange", presentTime, maxInstances-currentInstanceCount);
+        } else if (avg2Target > 1 && currentInstanceCount < maxInstances) {
+            owner.scaleToInstancesCount(newInstanceCount);
+            lastScaleUp = presentTime;
+            reporter.addDatapoint("Decision", presentTime, "Up");
+            reporter.addDatapoint("InstanceChange", presentTime, newInstanceCount - currentInstanceCount);
+        } else if (avg2Target < 1
+                && currentInstanceCount > minInstances
+                && TimeUtil.subtract(presentTime, lastScaleUp).getTimeAsDouble() > holdTime) {
+            owner.scaleToInstancesCount(newInstanceCount);
+            lastScaleUp = presentTime;
+            reporter.addDatapoint("Decision", presentTime, "Down");
+            reporter.addDatapoint("InstanceChange", presentTime, newInstanceCount - currentInstanceCount);
+        } else {
+            reporter.addDatapoint("Decision", presentTime, "Hold");
+            reporter.addDatapoint("InstanceChange", presentTime, 0);
+        }
+
+        if (owner.getInstancesCount() != currentInstanceCount) {
+            owner.sendTraceNote(String.format("Changed target instance count to %d", owner.getInstancesCount()));
+        }
+    }
+}