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CloudSim Plus: A modern, highly extensible and easier-to-use Java 8 Framework for Modeling and Simulation of Cloud Computing Infrastructures and Services

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/*
 * CloudSim Plus: A modern, highly-extensible and easier-to-use Framework for
 * Modeling and Simulation of Cloud Computing Infrastructures and Services.
 * http://cloudsimplus.org
 *
 *     Copyright (C) 2015-2018 Universidade da Beira Interior (UBI, Portugal) and
 *     the Instituto Federal de Educação Ciência e Tecnologia do Tocantins (IFTO, Brazil).
 *
 *     This file is part of CloudSim Plus.
 *
 *     CloudSim Plus is free software: you can redistribute it and/or modify
 *     it under the terms of the GNU General Public License as published by
 *     the Free Software Foundation, either version 3 of the License, or
 *     (at your option) any later version.
 *
 *     CloudSim Plus is distributed in the hope that it will be useful,
 *     but WITHOUT ANY WARRANTY; without even the implied warranty of
 *     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *     GNU General Public License for more details.
 *
 *     You should have received a copy of the GNU General Public License
 *     along with CloudSim Plus. If not, see .
 */
package org.cloudsimplus.autoscaling.resources;

import org.cloudbus.cloudsim.util.MathUtil;
import org.cloudbus.cloudsim.vms.Vm;
import org.cloudsimplus.autoscaling.VerticalVmScaling;

import java.util.function.Function;

/**
 * A {@link ResourceScaling} for which the capacity of the resource to be scaled will be instantaneously
 * resized to move the Vm from the under or overload state.
 * This way, the SLA violation time will be reduced.
 *
 * This scaling type will resize the resource capacity in the following way:
 * 

 *     in underload conditions: it decreases the resource capacity to be equal to the current load of the resource
 *     being scaled;
 *     in overload conditions: it increases the resource capacity to be equal to the current load of the resource
 *     being scaled.
 * 
 *
 * Finally it adds an extra amount of resource, defined by the {@link VerticalVmScaling#getScalingFactor() scaling factor},
 * for safety. This extra amount added is to enable the resource usage to grow up to the scaling factor
 * without needing to resize the resource again. If it grows up to the scaling factor,
 * a new up scaling request will be sent.
 * 
 *
 * If the scaling factor for this type of scaling is zero, it means that the scaling object
 * will always resize the resource to the exact amount that is being used.
 *
 * @author Manoel Campos da Silva Filho
 * @since CloudSim Plus 1.2.0
 */
public class ResourceScalingInstantaneous implements ResourceScaling {
    private static final ResourceScaling gradual = new ResourceScalingGradual();

    @Override
    public double getResourceAmountToScale(final VerticalVmScaling vmScaling) {
        final Function thresholdFunction = vmScaling.getResourceUsageThresholdFunction();
        /* Computes the size to which the resource has to be scaled to move it from the
        * under or overload state.*/
        final double newResourceSize =
            Math.ceil(vmScaling.getResource().getAllocatedResource() *
                MathUtil.HUNDRED_PERCENT / thresholdFunction.apply(vmScaling.getVm()));

        /*Includes and additional resource amount for safety, according to the scaling factor.
        * This way, if the resource usage increases again up to this extra amount,
        * there is no need to re-scale the resource.
        * If the scale factor is zero, no extra safety amount is included.*/
        final double extraSafetyCapacity = gradual.getResourceAmountToScale(vmScaling);
        return newResourceSize + extraSafetyCapacity;
    }
}