EC2Utils.java

//
// typica - A client library for Amazon Web Services
// Copyright (C) 2008 Xerox Corporation
// 
// 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.xerox.amazonws.ec2;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
import java.io.StringWriter;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * This class provides helper methods to interact with the Amazon EC2 service.
 *
 * @author D. Kavanagh
 * @author developer@dotech.com
 */
public class EC2Utils {
    private static Log logger = LogFactory.getLog(EC2Utils.class);

	/**
	 * This method makes a best effort to fetch all instance metadata.
	 *
	 * @return map of metadata
	 */
	public static Map<String, String> getInstanceMetadata() {
		HashMap<String, String> result = new HashMap<String, String>();
		int retries = 0;
		while (true) {
			try {
				URL url = new URL("http://169.254.169.254/latest/meta-data/");
				BufferedReader rdr = new BufferedReader(new InputStreamReader(url.openStream()));
				String line = rdr.readLine();
				while (line != null) {
					try {
						String val = getInstanceMetadata(line);
						result.put(line, val);
					} catch (IOException ex) {
						logger.error("Problem fetching piece of instance metadata!", ex);
					}
					line = rdr.readLine();
				}
				return result;
			} catch (IOException ex) {
				if (retries == 5) {
					logger.debug("Problem getting instance data, retries exhausted...");
					return result;
				}
				else {
					logger.debug("Problem getting instance data, retrying...");
					try { Thread.sleep((int)Math.pow(2.0, retries)*1000); } catch (InterruptedException e) {}
					retries++;
				}
			}
		}
	}

	/**
	 * This method makes a best effort to fetch a piece of instance metadata.
	 *
	 * @param key the name of the metadata to fetch
	 * @return value of the metadata item
	 */
	public static String getInstanceMetadata(String key) throws IOException {
		int retries = 0;
		String value = null;
		while (true) {
			try {
				URL url = new URL("http://169.254.169.254/latest/meta-data/"+key);
				value = new BufferedReader(new InputStreamReader(url.openStream())).readLine();
				return value;
			} catch (IOException ex) {
				if (retries == 5) {
					logger.debug("Problem getting instance data, retries exhausted...");
					logger.debug("value = "+value);
					return null;
				}
				else {
					logger.debug("Problem getting instance data, retrying...");
					try { Thread.sleep((int)Math.pow(2.0, retries)*1000); } catch (InterruptedException e) {}
					retries++;
				}
			}
		}
	}

	/**
	 * This method makes a best effort to fetch a piece of instance metadata.
	 *
	 * @param key the name of the metadata to fetch
	 * @return value of the metadata item
	 */
	public static String getInstanceUserdata() throws IOException {
		int retries = 0;
		while (true) {
			try {
				URL url = new URL("http://169.254.169.254/latest/user-data/");
				InputStreamReader rdr = new InputStreamReader(url.openStream());
				StringWriter wtr = new StringWriter();
				char [] buf = new char[1024];
				int bytes;
				while ((bytes = rdr.read(buf)) > -1) {
					if (bytes > 0) {
						wtr.write(buf, 0, bytes);
					}
				}
				rdr.close();
				return wtr.toString();
			} catch (IOException ex) {
				if (retries == 5) {
					logger.debug("Problem getting user data, retries exhausted...");
					return null;
				}
				else {
					logger.debug("Problem getting user data, retrying...");
					try { Thread.sleep((int)Math.pow(2.0, retries)*1000); } catch (InterruptedException e) {}
					retries++;
				}
			}
		}
	}

	/**
	 * This method encodes key/value pairs into a user-data string
	 *
	 */
	public static String encodeUserParams(Map<String, String> params) {
		StringBuilder ret = new StringBuilder();
		for (String key : params.keySet()) {
			ret.append(key);
			ret.append("=");
			ret.append(params.get(key));
			ret.append(";");
		}
		return ret.toString();
	}

	/**
	 * This method decodes key/value pairs from a user-data string
	 *
	 */
	public static Map<String, String> decodeUserParams(String params) {
		HashMap<String, String> result = new HashMap<String, String>();
		String param = params.substring(0, params.indexOf(';'));
		while (param != null) {
			int idx = param.indexOf('=');
			String key = param.substring(0, idx);
			String value = param.substring(idx+1);
			result.put(key, value);
			if (param.length() == params.length()-1) {
				param = null; // done
			}
			else {
				params = params.substring(params.indexOf(';')+1);
				param = params.substring(0, params.indexOf(';'));
			}
		}
		return result;
	}
}