com.amazonaws.regions.InstanceMetadataRegionProvider Maven / Gradle / Ivy

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The AWS SDK for Java with support for OSGi. The AWS SDK for Java provides Java APIs for building software on AWS' cost-effective, scalable, and reliable infrastructure products. The AWS Java SDK allows developers to code against APIs for all of Amazon's infrastructure web services (Amazon S3, Amazon EC2, Amazon SQS, Amazon Relational Database Service, Amazon AutoScaling, etc).

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/*
 * Copyright 2011-2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file 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 com.amazonaws.regions;

import com.amazonaws.AmazonClientException;
import com.amazonaws.util.EC2MetadataUtils;

import org.apache.commons.logging.LogFactory;

/**
 * Attempts to load region information from the EC2 Metadata service. If the application is not
 * running on EC2 this provider will return null.
 */
public class InstanceMetadataRegionProvider extends AwsRegionProvider {

    /**
     * Cache region as it will not change during the lifetime of the JVM.
     */
    private volatile String region;

    @Override
    public String getRegion() throws AmazonClientException {
        if (region == null) {
            synchronized (this) {
                if (region == null) {
                    this.region = tryDetectRegion();
                }
            }
        }
        return region;
    }

    private String tryDetectRegion() {
        try {
            return EC2MetadataUtils.getEC2InstanceRegion();
        } catch (AmazonClientException ace) {
            LogFactory.getLog(InstanceMetadataRegionProvider.class)
                    .debug("Ignoring failure to retrieve the region: " + ace.getMessage());
            return null;
        }
    }
}