com.elastisys.scale.cloudpool.commons.scaledown.strategies.NewestInstanceVictimSelectionStrategy Maven / Gradle / Ivy

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Common utility classes for building cloud pools.

There is a newer version: 5.2.3

package com.elastisys.scale.cloudpool.commons.scaledown.strategies;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import java.util.Collection;
import java.util.Comparator;

import com.elastisys.scale.cloudpool.api.types.Machine;
import com.elastisys.scale.cloudpool.commons.scaledown.VictimSelectionStrategy;

/**
 * A {@link VictimSelectionStrategy} that selects the most recently created
 * instance for termination.
 *
 *
 */
public enum NewestInstanceVictimSelectionStrategy implements VictimSelectionStrategy {

    /** The single instance of this class. */
    INSTANCE;

    @Override
    public Machine selectVictim(Collection candidates) throws IllegalArgumentException {
        checkNotNull(candidates, "null candidate set");
        checkArgument(!candidates.isEmpty(), "empty candidate set");

        return Machine.sort(candidates, new NewestFirstOrder()).get(0);
    }

    /**
     * {@link Comparator} that orders {@link Machine} instances in order of
     * increasing age (youngest instance first).
     *
     *
     *
     */
    public class NewestFirstOrder implements Comparator {
        @Override
        public int compare(Machine instance1, Machine instance2) {
            return instance2.getLaunchTime().compareTo(instance1.getLaunchTime());
        }
    }
}