api/src/main/java/com/datatorrent/api/StreamingApplication.java

/**
 * Copyright (C) 2015 DataTorrent, Inc.
 *
 * 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.datatorrent.api;

import org.apache.hadoop.conf.Configuration;

/**
 * Interface to be implemented for Java based streaming application declaration.
 * <p>
 * An application is the top level DAG with external configuration for
 * application master / engine settings, application specific properties or
 * overrides for individual operators in the DAG. <br>
 * Application launchers (CLI) use the interface to identify application DAGs
 * within jar files and supply the configuration upon instantiation.
 * <p>
 * Operator properties in the DAG can be configured externally. When an
 * application is launched from the CLI, any settings in dt-site.xml would
 * override property values in the DAG. It is therefore possible to have
 * defaults in the DAG code and supply environment/launch context specific
 * settings through the configuration.
 *
 * @since 0.3.2
 */
public interface StreamingApplication
{
  String DT_PREFIX = "dt.";
  /**
   * Launch mode for the application.
   * Used in the client to set configuration depending on how the DAG is executed.
   */
  String ENVIRONMENT = DT_PREFIX + "environment";

  /**
   * Streaming Application code would be executing in one of these environments.
   * ENVIRONMENT key in conf is set to LOCAL when the application is running in local mode.
   * It's set to CLUSTER when the application is running in distributed mode.
   */
  enum Environment
  {
    LOCAL,
    CLUSTER
  };

  /**
   * <p>populateDAG.</p>
   */
  void populateDAG(DAG dag, Configuration conf);

}