/**
* Copyright 2013 BlackLocus
*
* 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 com.blacklocus.qs.worker.aws;
import com.amazonaws.util.EC2MetadataUtils;
import com.blacklocus.qs.worker.QSWorkerIdService;
import com.blacklocus.qs.worker.simple.HostNameQSWorkerIdService;
import org.apache.commons.lang3.StringUtils;
import java.util.concurrent.atomic.AtomicReference;
/**
* Identifies this worker by its Amazon EC2 instance id {@link EC2MetadataUtils#getInstanceId()}. Caches the value
* after first lookup forever. If the read fails, defers to a fallback QSWorkerIdService -- The fallback value is not
* cached and consulted every invocation.
*
* @author Jason Dunkelberger (dirkraft)
*/
public class AmazonEC2WorkerIdService implements QSWorkerIdService {
public static final String PROP_SKIP_EC2_META = "com.blacklocus.qs.aws.disableEC2Meta";
private final QSWorkerIdService fallback;
private final AtomicReference<String> ec2id = new AtomicReference<String>();
/**
* Defaults fallback to {@link HostNameQSWorkerIdService}
*/
public AmazonEC2WorkerIdService() {
this(new HostNameQSWorkerIdService());
}
/**
* @param fallback in case the EC2 metadata lookup fails, most likely because this is not actually an EC2 instance.
* Disable EC2 checking and go straight to the fallback by setting {@link #PROP_SKIP_EC2_META} to
* <code>true</code>.
*/
public AmazonEC2WorkerIdService(QSWorkerIdService fallback) {
this.fallback = fallback;
}
@Override
public String getWorkerId() {
String id = ec2id.get();
if (null == id) {
if (!Boolean.valueOf(System.getProperty(PROP_SKIP_EC2_META, "false"))) {
id = EC2MetadataUtils.getInstanceId();
ec2id.set(id);
}
}
// Maybe ec2 meta was disabled, maybe it failed. Whatever: fall back.
if (StringUtils.isBlank(id)) {
id = fallback.getWorkerId();
}
return id;
}
}