LoadBalancingLog4jAppender.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.flume.clients.log4jappender;

import java.util.Properties;

import org.apache.commons.lang.StringUtils;
import org.apache.flume.FlumeException;
import org.apache.flume.api.RpcClientConfigurationConstants;
import org.apache.flume.api.RpcClientFactory;
import org.apache.flume.api.RpcClientFactory.ClientType;
import org.apache.log4j.helpers.LogLog;

/**
 *
 * Appends Log4j Events to an external Flume client which is decribed by the
 * Log4j configuration file. The appender takes the following required
 * parameters:
 * <p>
 * <strong>Hosts</strong> : A space separated list of host:port of the first hop
 * at which Flume (through an AvroSource) is listening for events.
 * </p>
 * <p>
 * <strong>Selector</strong> : Selection mechanism. Must be either ROUND_ROBIN,
 * RANDOM or custom FQDN to class that inherits from LoadBalancingSelector. If
 * empty defaults to ROUND_ROBIN
 * </p>
 * The appender also takes the following optional parameters:
 * <p>
 * <strong>MaxBackoff</strong> : A long value representing the maximum amount of
 * time in milliseconds the Load balancing client will backoff from a node that
 * has failed to consume an event
 * </p>
 * A sample log4j properties file which appends to a source would look like:
 *
 * <pre>
 * <p>
 * log4j.appender.out2 = org.apache.flume.clients.log4jappender.LoadBalancingLog4jAppender
 * log4j.appender.out2.Hosts = fooflumesource.com:25430 barflumesource.com:25430
 * log4j.appender.out2.Selector = RANDOM
 * log4j.logger.org.apache.flume.clients.log4jappender = DEBUG,out2</p>
 * </pre>
 * <p>
 * <pre>
 * <p>
 * log4j.appender.out2 = org.apache.flume.clients.log4jappender.LoadBalancingLog4jAppender
 * log4j.appender.out2.Hosts = fooflumesource.com:25430 barflumesource.com:25430
 * log4j.appender.out2.Selector = ROUND_ROBIN
 * log4j.appender.out2.MaxBackoff = 60000
 * log4j.logger.org.apache.flume.clients.log4jappender = DEBUG,out2</p>
 * </pre>
 * <p>
 * <i>Note: Change the last line to the package of the class(es), that will do
 * the appending.For example if classes from the package com.bar.foo are
 * appending, the last line would be:</i>
 * </p>
 *
 * <pre>
 * <p>log4j.logger.com.bar.foo = DEBUG,out2</p>
 * </pre>
 *
 *
 */
public class LoadBalancingLog4jAppender extends Log4jAppender {

  private String hosts;
  private String selector;
  private String maxBackoff;

  public void setHosts(String hostNames) {
    this.hosts = hostNames;
  }

  public void setSelector(String selector) {
    this.selector = selector;
  }

  public void setMaxBackoff(String maxBackoff) {
    this.maxBackoff = maxBackoff;
  }

  /**
   * Activate the options set using <tt>setHosts()</tt>, <tt>setSelector</tt>
   * and <tt>setMaxBackoff</tt>
   *
   * @throws FlumeException
   *           if the LoadBalancingRpcClient cannot be instantiated.
   */
  @Override
  public void activateOptions() throws FlumeException {
    try {
      final Properties properties = getProperties(hosts, selector, maxBackoff);
      rpcClient = RpcClientFactory.getInstance(properties);
    } catch (FlumeException e) {
      String errormsg = "RPC client creation failed! " + e.getMessage();
      LogLog.error(errormsg);
      throw e;
    }
  }

  private Properties getProperties(String hosts, String selector,
      String maxBackoff) throws FlumeException {

    if (StringUtils.isEmpty(hosts)) {
      throw new IllegalArgumentException("hosts must not be null");
    }

    Properties props = new Properties();
    String[] hostsAndPorts = hosts.split("\\s+");
    StringBuilder names = new StringBuilder();
    for (int i = 0; i < hostsAndPorts.length; i++) {
      String hostAndPort = hostsAndPorts[i];
      String name = "h" + i;
      props.setProperty(RpcClientConfigurationConstants.CONFIG_HOSTS_PREFIX + name,
          hostAndPort);
      names.append(name).append(" ");
    }
    props.put(RpcClientConfigurationConstants.CONFIG_HOSTS, names.toString());
    props.put(RpcClientConfigurationConstants.CONFIG_CLIENT_TYPE,
        ClientType.DEFAULT_LOADBALANCE.toString());
    if (!StringUtils.isEmpty(selector)) {
      props.put(RpcClientConfigurationConstants.CONFIG_HOST_SELECTOR, selector);
    }

    if (!StringUtils.isEmpty(maxBackoff)) {
      long millis = Long.parseLong(maxBackoff.trim());
      if (millis <= 0) {
        throw new IllegalArgumentException(
            "Misconfigured max backoff, value must be greater than 0");
      }
      props.put(RpcClientConfigurationConstants.CONFIG_BACKOFF,
          String.valueOf(true));
      props.put(RpcClientConfigurationConstants.CONFIG_MAX_BACKOFF, maxBackoff);
    }
    return props;
  }
}