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Common utility classes for building Amazon AWS-based cloud pools.

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package com.elastisys.scale.cloudpool.aws.commons.requests.autoscaling;

import static com.elastisys.scale.cloudpool.aws.commons.predicates.InstancePredicates.inAnyOfStates;

import java.util.concurrent.Callable;
import java.util.concurrent.TimeUnit;

import com.amazonaws.ClientConfiguration;
import com.amazonaws.auth.AWSCredentials;
import com.amazonaws.services.autoscaling.model.TerminateInstanceInAutoScalingGroupRequest;
import com.amazonaws.services.ec2.model.Instance;
import com.elastisys.scale.cloudpool.aws.commons.client.Ec2ApiClient;
import com.elastisys.scale.cloudpool.aws.commons.requests.ec2.GetInstance;
import com.elastisys.scale.commons.net.retryable.Retryable;
import com.elastisys.scale.commons.net.retryable.Retryers;

/**
 * A {@link Callable} task that, when executed, requests a particular Auto
 * Scaling Group member instance to be terminated. As a side-effect, the desired
 * capacity of the Auto Scaling Group is decremented. The task also waits for
 * the instance to appear terminating/terminated in {@code DescribeInstances}.
 * 
 * Due to the eventual consistency semantics of the Amazon API, operations may
 * need time to propagate through the system and results may not be immediate.
 */
public class TerminateAutoScalingGroupInstance
		extends AmazonAutoScalingRequest {

	/** The machine instance identifier to be terminated. */
	private final String instanceId;

	public TerminateAutoScalingGroupInstance(AWSCredentials awsCredentials,
			String region, ClientConfiguration clientConfig,
			String instanceId) {
		super(awsCredentials, region, clientConfig);
		this.instanceId = instanceId;
	}

	@Override
	public Void call() {
		TerminateInstanceInAutoScalingGroupRequest request = new TerminateInstanceInAutoScalingGroupRequest()
				.withInstanceId(this.instanceId)
				.withShouldDecrementDesiredCapacity(true);
		getClient().getApi().terminateInstanceInAutoScalingGroup(request);

		awaitTermination(this.instanceId);
		return null;
	}

	private void awaitTermination(String instanceId) {
		String name = String.format("await-terminal-state{%s}", instanceId);
		try (Ec2ApiClient ec2Client = new Ec2ApiClient(getAwsCredentials(),
				getRegion(), getClientConfig())) {
			Callable stateRequester = new GetInstance(
					getAwsCredentials(), getRegion(), getClientConfig(),
					instanceId);

			int initialDelay = 1;
			int maxRetries = 8;
			Retryable retryer = Retryers.exponentialBackoffRetryer(
					name, stateRequester, initialDelay, TimeUnit.SECONDS,
					maxRetries, inAnyOfStates("shutting-down", "terminated"));
			try {
				retryer.call();
			} catch (Exception e) {
				throw new RuntimeException(String.format(
						"gave up waiting for instance to terminate: '%s': %s",
						instanceId, e.getMessage()), e);
			}
		}
	}
}