WorkflowToken Enhancements

User Stories

As a developer of the Workflow application -

• I want the ability to pass the custom data (such as metric, status, error codes etc.) from one program in the Workflow to the next subsequent programs in the form of token. 
• At any node in the Workflow, I want ability to query the data from the token.
• I want ability to fetch the data from the token which was set by a specific node.  
• I want ability to find the name of the node which most recently set the token value for the specific key e.g. node who last set the ERROR flag in the token, so that I can take appropriate action (such as logging or improving its code) on it.
• I want to have the conditional execution in the Workflow based on the information contained in the token.
• I want to terminate the execution if some node in the Workflow produce unexpected results.

As an admin/support person/developer of the Workflow application -

• I want ability to query the WorkflowToken from the past runs for running analysis such as which node is executed more frequently and why.
• I want ability to query the token values which were added by the specific node in the Workflow to debug the flow of execution. 

Requirements

• Generic Token support (not only MR counters)

• Ability for the user to access the token set by any node in the Workflow
• Persist token per Workflow run in the MDS
• View token set by specific node in the Workflow

Assumptions

• Generic information in the token is of the key-value type, each represented by String.

Potential Changes

• WorkflowToken interface changes

  /**
   * Interface to represent the data that is transferred from one node to the next nodes in the {@link Workflow}.
   */
  @Beta
  public interface WorkflowToken {
  
    /**
     * Keys in the {@link WorkflowToken} can be added by user, using the
     * {@link WorkflowToken#put} method. These keys are added under the {@link Scope#USER} scope.
     * CDAP also adds some keys to the {@link WorkflowToken}. for e.g. MapReduce counters.
     * The keys added by CDAP gets added under {@link Scope#SYSTEM} scope.
     */
    public enum Scope {
      USER,
      SYSTEM
    }
  
    /**
     * Put the specified key-value entry into the {@link WorkflowToken}.
     * The token may store additional information about the context in which
     * this key is being set, for example, the unique name of the workflow node.
     * @param key the key representing the entry
     * @param value the value for the key
     */
    // TODO [CDAP-2895] put operation should throw certain exceptions
    void put(String key, String value);
  
    /**
     * Get the most recent value for the specified key.
     * @param key the key to be searched
     * @return the {@link Value} for the key
     */
    @Nullable
    Value get(String key);
  
    /**
     * Get the most recent value for the specified key for a given scope.
     * @param key the key to be searched
     * @param scope the {@link WorkflowToken.Scope} for the key
     * @return the {@link Value} for the key from the specified scope
     */
    @Nullable
    Value get(String key, Scope scope);
  
    /**
     * Get the value set for the specified key by the specified node.
     * @param key the key to be searched
     * @param nodeName the name of the node
     * @return the {@link Value} set for the key by nodeName
     */
    @Nullable
    Value get(String key, String nodeName);
  
    /**
     * Get the value set for the specified key by the specified node for a given scope.
     * @param key the key to be searched
     * @param nodeName the name of the node
     * @param scope the {@link WorkflowToken.Scope} for the key
     * @return the {@link Value} set for the key by nodeName for a given scope
     */
    @Nullable
    Value get(String key, String nodeName, Scope scope);
  
    /**
     * Same key can be added to the WorkflowToken by multiple nodes.
     * This method returns the {@link List} of {@link NodeValueEntry}, where
     * each entry represents the unique node name and the value that it set
     * for the specified key.
     * <p>
     * The list maintains the order in which the values were
     * inserted in the WorkflowToken for a specific key except in the case of fork
     * and join. In case of fork in the Workflow, copies of the WorkflowToken are made
     * and passed along each branch. At the join, all copies of the
     * WorkflowToken are merged together. While merging, the order in which the values were
     * inserted for a specific key is guaranteed within the same branch, but not across
     * different branches.
     * @param key the key to be searched
     * @return the list of {@link NodeValueEntry} from node name to the value that node
     * added for the input key
     */
    List<NodeValueEntry> getAll(String key);
  
    /**
     * Same key can be added to the WorkflowToken by multiple nodes.
     * This method returns the {@link List} of {@link NodeValueEntry}, where
     * each entry represents the unique node name and the value that it set
     * for the specified key.
     * <p>
     * The list maintains the order in which the values were
     * inserted in the WorkflowToken for a specific key except in the case of fork
     * and join. In case of fork in the Workflow, copies of the WorkflowToken are made
     * and passed along each branch. At the join, all copies of the
     * WorkflowToken are merged together. While merging, the order in which the values were
     * inserted for a specific key is guaranteed within the same branch, but not across
     * different branches.
     * @param key the key to be searched
     * @param scope the {@link WorkflowToken.Scope} for the key
     * @return the list of {@link NodeValueEntry} from node name to the value that node
     * added for the input key for a given scope
     */
    List<NodeValueEntry> getAll(String key, Scope scope);
  
    /**
     * Get the {@link Map} of key-values that were added to the {@link WorkflowToken}
     * by specific node.
     * @param nodeName the unique name of the node
     * @return the map of key to values that were added by the specified node
     */
    Map<String, Value> getAllFromNode(String nodeName);
  
    /**
     * Get the {@link Map} of key-values that were added to the {@link WorkflowToken}
     * by specific node.
     * @param nodeName the unique name of the node
     * @param scope the {@link WorkflowToken.Scope} for the key
     * @return the map of key to values that were added by the specified node for a given scope
     */
    Map<String, Value> getAllFromNode(String nodeName, Scope scope);
  
    /**
     * This method is deprecated as of release 3.1.
     * Get the Hadoop counters from the previous MapReduce program in the Workflow.
     * The method returns null if the counters are not set.
     * @return the Hadoop MapReduce counters set by the previous MapReduce program
     */
    @Deprecated
    @Nullable
    Map<String, Map<String, Long>> getMapReduceCounters();
  
    /**
     * Return true if the {@link WorkflowToken} contains the specified key.
     * @param key the key to be tested for the presence in the {@link WorkflowToken}
     * @return the result of the test
     */
    boolean containsKey(String key);
  
    /**
     * Return true if the {@link WorkflowToken} contains the specified key.
     * @param key the key to be tested for the presence in the {@link WorkflowToken}
     * @param scope the {@link WorkflowToken.Scope} for the key
     * @return the result of the test
     */
    boolean containsKey(String key, Scope scope);
  }
   

  
  The method getAll(String key) in the above interface returns the List of NodeValueEntry objects. NodeValueEntry class represents nodeName and value that the node put for the specific key.

  /**
   * Multiple nodes in the Workflow can add the same key to the {@link WorkflowToken}.
   * This class provides a mapping from node name to the value which was set for the
   * specific key.
   */
  public final class NodeValueEntry {
    private final String nodeName;
    private final Value value;
  
    public NodeValueEntry(String nodeName, String value) {
      this.nodeName = nodeName;
      this.value = value;
    }
  
    public String getNodeName() {
      return nodeName;
    }
  
    public Value getValue() {
      return value;
    }
    
    ...
    // other methods like toString(), equals() and hashCode()		 
    ...
  }

  
  The details of the Value class are as follows:

  /**
   * Represents the value for the specific key in the {@link WorkflowToken}
   */
  public final class Value {
    private final String value;
  
    public Value(String value) {
      this.value = value;
    }
  
    public String toString() {
      return value;
    }
  
    public long getAsLong() {
      return Long.parseLong(value);
    }
  }

• Ability to include same program multiple times in the Workflow

  Use Case: Email campaign generates two categories of events - send events (SUCCESS, FAIL) and tracking events (OPEN, CLICK etc.). Records representing the send event and tracking event have different number of fields. These two categories of the events are sent to CDAP using streams "send" and "tracking".

  Tracking event format:

  audience_id,event_type,ip_address,device_type,event_time,link

  Example records:

  bob,CLICK,192.168.29.10,android,1436311150092,http://www.somedomain.com

  adam,CLICK,192.168.29.18,ipad,1436311232276,http://www.anotherdomain.com

  Send event format:

  audience_id::event_sub_type::ip_address::deliveryCode::event_time

  Example records:

  bob::SEND::192.168.29.10::SUCCESS::1436311232276

  adam::SEND::192.168.29.9::SUCCESS::1436311434476

  Solution: 

  Same MapReduce program "EventParser" can be used in the Workflow to parse these two categories of the events in parallel and create the list Event object per audience id. 

  Step 1: Add same MapReduce/Spark program multiple times in the Application.

  API changes for the ApplicationConfigurer to allow adding MapReduce/Spark program in the Application with the explicit name.

  /**
   * Adds a {@link MapReduce} to the Application.
   * @param name the name to be given to the {@link MapReduce} program
   * @param mapReduce the {@link MapReduce} program to be included in the Application
   */
  void addMapReduce(String name, MapReduce mapReduce);
   
  /**
   * Adds a {@link Spark} to the Application.
   * @param name the name to be given to the {@link Spark} program
   * @param spark the {@link Spark} program to be included in the Application
   */
  void addSpark(String name, Spark spark);
  

  EventParser application:

  public class EventParserApp extends AbstractApplication {
    @Override
    public void configure() {
  	// Stream to receive send events
  	addStream(new Stream("send"));
   	// Stream to receive tracking events
  	addStream(new Stream("tracking"));
   
      // Add EventParser MapReduce program multiple times in the application with different properties
    	Map<String, String> properties = Maps.newHashMap();
  	properties.put("input.stream", "tracking");
  	// 'trackingParser' is instance of the EventParser which will read the 'tracking' stream 
  	addMapReduce("trackingParser", new EventParser(properties));
  
  	properties = Maps.newHashMap();
  	properties.put("input.stream", "send");
  	// 'sendParser' is instance of the EventParser which will read the 'send' stream 
  	addMapReduce("sendParser", new EventParser(properties));
   
  	// Add Workflow which will process the tracking and send events in parallel
  	addWorkflow(new EventParserWorkflow());
    }
  }

  EventParser MapReduce program:

  public class EventParser extends AbstractMapReduce {
  
    private final Map<String, String> properties;
    public EventParser(Map<String, String> properties) {
      this.properties = properties;
    }
   
    @Override
    public void configure() {
      setDescription("MapReduce program for parsing the email events and storing them in the dataset.");
      // Serialize the properties
    	setProperties(properties);
    	setOutputDataset("events");
    }
   
    @Override
    public void beforeSubmit(MapReduceContext context) throws Exception {
    	Job job = context.getHadoopJob();
    	job.setMapperClass(EventParserMapper.class);
    	job.setReducerClass(EventParserReducer.class);
  
    	job.setMapOutputKeyClass(Text.class);
    	job.setOutputValueClass(Event.class);
  
    	job.setNumReduceTasks(1);
  	String streamToVerify = context.getSpecification().getProperties().get("input.stream");
    	job.getConfiguration().set("input.stream", streamToVerify);
  
    	// Read the purchase events from the last 60 minutes as input to the mapper.
    	final long endTime = context.getLogicalStartTime();
    	final long startTime = endTime - TimeUnit.MINUTES.toMillis(60);
    	StreamBatchReadable.useStreamInput(context, streamToVerify, startTime, endTime);
    }
  }
   
  // EventParserMapper
  public static class EventParserMapper extends Mapper<LongWritable, Text, Text, Event>  {
  
    @Override
    public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
      String logEvent = value.toString();
      if (logEvent.isEmpty()) {
        return;
      }
      
      String inputStream = context.getConfiguration().get("input.stream");
      Event event;
      if(inputStream.equals("send")) {
        event = getSendEvent(logEvent);
      } else {
        event = getTrackingEvent(logEvent);
      }
      if (event != null) {
        context.write(new Text(event.getAudienceId()), event);
      }
    }
    
    private Event getSendEvent(String logEvent) {
      String seperator = "::";
      int fieldLength = 5;
      String[] fields = logEvent.split(seperator);
      if (fields.length != fieldLength) {
        return null;
      }
      String audienceId = fields[0];
      String eventType = fields[1];
      String ipAddress = fields[2];
      String deliveryCode = fields[3];
      String eventTime = fields[4];
      
      return new Event(audienceId, eventType, ipAddress, eventTime, deliveryCode)
    }
    
    private Event getTrackingEvent(String logEvent) {
      String seperator = ",";
      int fieldLength = 6;
      String[] fields = logEvent.split(seperator);
      if (fields.length != fieldLength) {
        return null;
      }
      String audienceId = fields[0];
      String eventType = fields[1];
      String ipAddress = fields[2];
      String deviceType = fields[3];
      String eventTime = fields[4];
      String link = fields[5];
      return new Event(audienceId, eventType, ipAddress, eventTime, deviceType + "&&" + link);
    }
  }
   

  EventParserWorkflow:

  public class EventParserWorkflow extends AbstractWorkflow {
    @Override
    protected void configure() {
      fork()
        .addMapReduce("trackingParser")
      .also()
        .addMapReduce("sendParser")
      .join();
    }
  }

   

  Step 2: WorkflowConfigurer interface changes

  With the API changes mentioned in the above section, same program (MapReduce/Spark) can be added multiple times in the Application with different names and parameters. These programs can be referred to in the Workflow. However in order to add same action multiple times in the Workflow, we still need to specify the unique name.  

  The WorkflowConfigurer API can be updated to allow a user to set a unique name for the Workflow action, if it occurs multiple times in a Workflow and use that unique name to retrieve the token.
  
  

   /**
     * {@link Workflow} consists of multiple {@link WorkflowNode}s.
     * Same Workflow action can be added multiple times in the {@link Workflow} at
     * different {@link WorkflowNode}s.
     * <p>
     * This method allows associating the uniqueName to the {@link WorkflowNode}
     * which represents the Workflow action. The uniqueName helps querying for the
     * values that were added to the {@link WorkflowToken} by the particular node.
     * <p>
     * The uniqueName must be unique across all {@link WorkflowNode} in the Workflow,
     * otherwise the Application deployment will fail.
     * @param uniqueName the uniqueName to be assigned to the {@link WorkflowNode}
     *                   which represents the Spark program
     * @param action the action to be added to the {@link Workflow}
     * @return the configurer for the current condition
     */
    WorkflowForkConfigurer<T> addAction(String uniqueName, WorkflowAction action);

  
  WorkflowToken can also be updated from a predicate on the condition node. In the presence of multiple condition nodes in a Workflow, we will need the ability to specify unique names for the conditions as well so that token values from specific condition nodes can be fetched. 

  /**
   * Adds a condition with the unique name to the {@link Workflow}.
   * @param conditionName the unique name to be assigned to the condition
   * @param condition     the {@link Predicate} to be evaluated for the condition
   * @return the configurer for the condition
   */
  WorkflowConditionConfigurer<? extends WorkflowConfigurer> condition(String conditionName, Predicate<WorkflowContext> condition);

• Provide ability to set and get information in the WorkflowToken
  
  1. MapReduce program: Users should be able to access and modify WorkflowToken from "beforeSubmit" and "onFinish" methods of the MapReduce program. Since these methods get the MapReduceContext, we will need to update the MapReduceContext interface to get the WorkflowToken.

  /**
   * If {@link MapReduce} program is executed as a part of the {@link Workflow} 
   * then get the {@link WorkflowToken} associated with the current run, otherwise return null.  
   * @return the {@link WorkflowToken} if available
   */
  @Nullable
  WorkflowToken getWorkflowToken();

  
  

  Consider the following code sample to update the WorkflowToken in the MapReduce program:

  @Override
  public void beforeSubmit(MapReduceContext context) throws Exception {
    ...
    WorkflowToken workflowToken = context.getWorkflowToken();
    if (workflowToken != null) {
      // Put the action type in the WorkflowToken
      workflowToken.put("action_type", "MAPREDUCE");
      // Put the start time for the action
      workflowToken.put("startTime", String.valueOf(System.currentTimeMillis()));
    }
    ...
  }
   
  @Override
  public void onFinish(boolean succeeded, MapReduceContext context) throws Exception {
    ...
    WorkflowToken workflowToken = context.getWorkflowToken();
    if (workflowToken != null) {
      // Put the end time for the action 
      workflowToken.put("endTime", String.valueOf(System.currentTimeMillis()));
    }
    ...
  }
  

  2. Spark program: Users should be able to access and modify WorkflowToken from "beforeSubmit" and "onFinish" methods of the Spark program. Since these methods get the SparkContext, we will need to update the SparkContext interface to get the WorkflowToken.

   

  /**
   * If {@link Spark} program is executed as a part of the {@link Workflow}
   * then get the {@link WorkflowToken} associated with the current run, otherwise return null.
   * @return the {@link WorkflowToken} if available
   */
  @Nullable
  WorkflowToken getWorkflowToken();

  3. Custom Workflow action: Since custom workflow actions already receive WorkflowContext, no changes are anticipated in the interface.
  
  

  Following is the sample code to get values from the WorkflowToken in custom action:

  @Override
  public void run() {
    ...
    WorkflowToken token = getContext().getToken();
    // set the type of the action of the current node	
    token.put("action_type", "CUSTOM_ACTION");
   
    // Assume that we have the following Workflow 
   
    //												|------->PurchaseByCustomer------->|
    //										True	|								   |	
    // Start---->RecordVerifier---->Predicate-------->|								   |------------->StatusReporter----->End 	
    //								  |				| 								   |	    |
    //								  | False		|------->PurchaseByProduct-------->|        |
    //                                  |                        									|
    //                                  |--------------------->ProblemLogger--------------------->|
   
    
    // Use case 1: Predicate can add the key "branch" in the WorkflowToken with value as "true" if true branch will be executed
    // or "false" otherwise. In "StatusReporter" in order to get which branch in the Workflow was executed
    boolean bTrueBranch = Boolean.parseBoolean(token.get("branch"));
   
    // Use case 2: User may want to compare the counters emitted by "PurchaseByCustomer" and "PurchaseByProduct", in order to find which job
    // is processing more records. 
    String purchaseByCustomerCounterValue = token.get("MapReduceCounterName", "PurchaseByCustomer");
    String purchaseByProductCounterValue = token.get("MapReduceCounterName", "PurchaseByProduct");
    
    // Use case 3: Since Workflow can have multiple complex conditions and forks in its structure, in the "StatusReporter", 
    // user may want to  know how many actions were executed as a part of this run. If the number of nodes executed were below
    // certain threshold send an alert. Assuming that every node in the Workflow adds the key "action_type" with the value as action
    // type for node in the WorkflowToken, user can further figure out the break down by action type in the particular Workflow run.
    List<NodeValueEntry> nodeValues = token.getAll("action_type");
    int totalNodeExecuted = nodeValues.size();
    int mapReduceNodes = 0;
    int sparkNodes = 0;
    int customActionNodes = 0;
    int conditions = 0;
    for (NodeValueEntry entry : nodeValues) {
      if (entry.getValue().equals("MAPREDUCE")) {
        mapReduceNodes++;
      } 
      if (entry.getValue().equals("SPARK")) {
        sparkNodes++;
      } 
      if (entry.getValue().equals("CUSTOM_ACTION")) {
        customActionNodes++;
      }
      if (entry.getValue().equals("CONDITION")) {
        conditions++;
      }
    }
  
    // Use case 4: To get the name of the last node which set the "ERROR" flag in the WorkflowToken
    List<NodeValueEntry> errorNodeValueList = token.getAll("ERROR");
    String nodeNameWhoSetTheErrorFlagLast = errorNodeValueList.get(errorNodeValueList.size() - 1);
   
    // To get the start time of the MapReduce program with unique name "PurchaseHistoryBuilder"
    String startTime = token.get("startTime", "PurchaseHistoryBuilder");
   
    // To get the most recent value of counter with group name
    // 'org.apache.hadoop.mapreduce.TaskCounter' and counter name 'MAP_INPUT_RECORDS'
    
    String flattenCounterKey = "mr.counters.org.apache.hadoop.mapreduce.TaskCounter.MAP_INPUT_RECORDS";
    workflowToken.get(flattenCounterKey);
  
    // To get the value of counter with group name 'org.apache.hadoop.mapreduce.TaskCounter'
    // and counter name 'MAP_INPUT_RECORDS' as set by MapReduce program with unique name 'PurchaseHistoryBuilder'
    workflowToken.get(flattenCounterKey, "PurchaseHistoryBuilder");
   ...
  }

• WorkflowToken in presence of Fork and Join
  When a fork is encountered in the Workflow, we make a copy of the WorkflowToken and pass it along to each branch. At the join, we create a new WorkflowToken, which will be a merge of the WorkflowTokens associated with each of the branches of the fork. Since we are storing the information in the token at the node level, there will not be any conflicts during the merge process.
  
  
• Persisting the WorkflowToken
  The RunRecord for the Workflow will contain the WorkflowToken as its property. This token will be updated before the execution of the action in the Workflow. We will add a version field to the RunRecord itself which will help in the upgrade process.
  
  
• RESTful end-points to access the value of the WorkflowToken that was received by an individual node in the Workflow
  We will expose a RESTful end point to retrieve the token values that were set by a particular node as identified by its unique name.

   

  /apps/{app-id}/workflows/{workflow-name}/runs/{run-id}/nodes/{unique-node-name}/token

  REST API	Response	Comments	Reviewed?
  /namespaces/{namespace-id}/apps/{app-id}/workflows/{workflow-name}/runs/{run-id}/token	Json containing the entire workflow token for a particular workflow run e.g. { "tokenValueMap": { "key1": [ { "nodeName": "node1", "value": "value1" }, { "nodeName": "node2", "value": "value2" } ], "key2": [ { "nodeName": "node2", "value": "v2" } ] } } Response Codes:  200 if successful 404 if app/workflow not found 500 if there is an internal error
  /namespaces/{namespace-id}/apps/{app-id}/workflows/{workflow-name}/runs/{run-id}/nodes/{unique-node-name}/token	{ "key1": "value1", "key2": "value2 } Response Codes:  200 if successful 404 if app/workflow not found 500 if there is an internal error