/**
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.aurora.scheduler.updater.strategy;

import java.util.Set;

/**
 * A strategy that chooses which instances in a group to update next.
 */
public interface UpdateStrategy<T> {

  /**
   * Gets the next group to update.
   *
   * @param idle Idle instances, candidate for being updated.
   * @param active Instances currently being updated.
   * @return A subset of {@code idle}, instances to start updating.
   */
  Set<T> getNextGroup(Set<T> idle, Set<T> active);
}