Task Interface

The task interface contains two methods: run and cancel. User can implement his or her own logic in run function and cancel / roll back logic in cancel function.

public class MyTask implements Task {
  @Override
  TaskResult run() {
    // Task logic
  }
 
  @Override
  void cancel() {
    // Cancel logic
  }
}

TaskConfig

In helix, usually an object config represents the abstraction of that object, such as TaskConfig, JobConfig and WorkflowConfig. TaskConfig contains configurable task conditions. TaskConfig does not require to have any input to create a new object:

TaskConfig taskConfig = new TaskConfig(null, null, null, null);

For these four fields:

• Command: The task command, will use Job command if this is null
• ID: Task unique id, will generate a new ID for this task if input is null
• TaskTargetPartition: Target partition of a target. Could be null
• ConfigMap: Task property key-value map containing all other property stated above, such as command, ID.

Share Content Across Tasks and Jobs

Task framework also provides a feature that user can store the key-value data per task, job and workflow. The content stored at workflow layer can shared by different jobs belong to this workflow. Similarly, content persisted at job layer can shared by different tasks nested in this job. Currently, user can extend the abstract class UserContentStore and use two methods putUserContent and getUserContent. It's similar to HashMap put and get method except for the additional param Scope. The Scope defines which layer this key-value pair to be persisted.

public class MyTask extends UserContentStore implements Task {
  @Override
  TaskResult run() {
    putUserContent("KEY", "WORKFLOWVALUE", SCOPE.WORKFLOW);
    putUserContent("KEY", "JOBVALUE", SCOPE.JOB);
    putUserContent("KEY", "TASKVALUE", SCOPE.TASK);
    String taskValue = getUserContent("KEY", SCOPE.TASK);
  }
 ...
}

Return Task Results

User can define the TaskResult for a task once it is at final stage (complete or failed). The TaskResult contains two fields: status and info. Status is current Task Status including COMPLETED, CANCELLED, FAILED and FATAL_FAILED. The difference between FAILED and FATAL_FAILED is that once the task defined as FATAL_FAILED, helix will not do the retry for this task and abort it. The other field is information, which is a String type. User can pass any information including error message, description and so on.

TaskResult run() {
    ....
    return new TaskResult(TaskResult.Status.FAILED, "ERROR MESSAGE OR OTHER INFORMATION");
}

Task Retry and Abort

Helix provides retry logics to users. User can specify the number of task failures to allow under a job. It is a method will be introduced in Following Job Section. Another choice offered to user that if user thinks a task is very critical and do not want to do the retry once it is failed, user can return a TaskResult stated above with FATAL_FAILED status. Then Helix will not do the retry for that task.

return new TaskResult(TaskResult.Status.FATAL_FAILED, "DO NOT WANT TO RETRY, ERROR MESSAGE");

TaskDriver

All the control operation related to workflow and job are based on TaskDriver object. TaskDriver offers several APIs to controller, modify and track the tasks. Those APIs will be introduced in each section when they are necessary. TaskDriver object can be created either by HelixManager or ZkClient with cluster name:

HelixManager manager = new ZKHelixManager(CLUSTER_NAME, INSTANCE_NAME, InstanceType.PARTICIPANT, ZK_ADDRESS);
TaskDriver taskDriver1 = new TaskDriver(manager);
 
TaskDriver taskDriver2 = new TaskDriver(zkclient, CLUSTER_NAME);

Propagate Task Error Message to Helix

When task encounter an error, it could be returned by TaskResult. Unfortunately, user can not get this TaskResult object directly. But Helix provides error messages persistent. Thus user can fetch the error messages from Helix via TaskDriver, which introduced above. The error messages will be stored in Info field per Job. Thus user have to get JobContext, which is the job status and result object.

taskDriver.getJobContext("JOBNAME").getInfo();

One-time Workflow

As common use, one-time workflow will be the default workflow as user created. The first step is to create a WorkflowConfig.Builder object with workflow name. Then all configs can be set in WorkflowConfig.Builder. Once the configuration is done, WorkflowConfig object can be got from WorkflowConfig.Builder object. We have two rules to validate the Workflow configuration:

• Expiry time should not be less than 0
• Schedule config should be valid either one-time or a positive interval magnitude (Recurrent workflow)

Example:

Workflow.Builder myWorkflowBuilder = new Workflow.Builder("MyWorkflow");
myWorkflowBuilder.setExpiry(5000L);
Workflow myWorkflow = myWorkflowBuilder.build();

Recurrent Workflow

Recurrent workflow is the workflow scheduled periodically. The only config different from One-time workflow is to set a recurrent ScheduleConfig. There two methods in ScheduleConfig can help you to create a ScheduleConfig object: recurringFromNow and recurringFromDate. Both of them needs recurUnit (time unit for recurrent) and recurInteval (magnitude of recurrent interval). Here's the example:

ScheduleConfig myConfig1 = ScheduleConfig.recurringFFromNow(TimeUnit.MINUTES, 5L);
ScheduleConfig myConfig2 = ScheduleConfig.recurringFFromDate(Calendar.getInstance.getTime, TimeUnit.HOURS, 10L);

Once this schedule config is created. It could be set in the workflow config:

Workflow.Builder myWorkflowBuilder = new Workflow.Builder("MyWorkflow");
myWorkflowBuilder.setExpiry(2000L)
                 .setScheduleConfig(ScheduleConfig.recurringFromNow(TimeUnit.DAYS, 5));
Workflow myWorkflow = myWorkflowBuilder.build();

Start a Workflow

Start a workflow is just using taskdrive to start it. Since this is an async call, after start the workflow, user can keep doing actions.

taskDriver.start(myWorkflow);

Stop a Workflow

Stop workflow can be executed via TaskDriver:

taskDriver.stop(myWorkflow);

Resume a Workflow

Once the workflow is stopped, it does not mean the workflow is gone. Thus user can resume the workflow that has been stopped. Using TaskDriver resume the workflow:

taskDriver.resume(myWorkflow);

Delete a Workflow

Similar to start, stop and resume, delete operation is supported by TaskDriver.

taskDriver.delete(myWorkflow);

Add a Job

WARNING: Job can only be added to WorkflowConfig.Builder. Once WorkflowConfig is built, no job can be added! For creating a Job, please refer to the following section (Create a Job)

myWorkflowBuilder.addJob("JobName", jobConfigBuilder);

Add a Job dependency

Jobs can have dependencies. If one job2 depends on job1, job2 will not be scheduled until job1 finished.

myWorkflowBuilder.addParentChildDependency(ParentJobName, ChildJobName);

Schedule a workflow for executing in a future time

Application can create a workflow with a ScheduleConfig so as to schedule it to be executed in a future time.

myWorkflowBuilder.setScheduleConfig(ScheduleConfig.oneTimeDelayedStart(new Date(inFiveSeconds)));

Additional Workflow Options

Add Tasks

There are two ways of adding tasks:

• Add by TaskConfig. Tasks can be added via adding TaskConfigs. User can create a List of TaskConfigs or add TaskConfigMap, which is a task id to TaskConfig mapping.

TaskConfig taskCfg = new TaskConfig(null, null, null, null);
List<TaskConfig> taskCfgs = new ArrayList<TaskConfig>();
myJobCfg.addTaskConfigs(taskCfgs);
 
Map<String, TaskConfig> taskCfgMap = new HashMap<String, TaskConfig>();
taskCfgMap.put(taskCfg.getId(), taskCfg);
myJobCfg.addTaskConfigMap(taskCfgMap);

• Add by Job command. If user does not want to specify each TaskConfig, we can create identical tasks based on Job command with number of tasks.

myJobCfg.setCommand("JobCommand").setNumberOfTasks(10);

WARNING: Either user provides TaskConfigs / TaskConfigMap or both of Job command and number tasks (except Targeted Job, refer following section) . Otherwise, validation will be failed.

Generic Job

Generic Job is the default job created. It does not have targeted resource. Thus this generic job could be assigned to one of eligble instances.

Targeted Job

Targeted Job has set up the target resource. For this kind of job, Job command is necessary, but number of tasks is not. The tasks will depends on the partion number of targeted resource. To set target resource, just put target resource name to JobConfig.Builder.

myJobCfgBuilder.setTargetResource("TargetResourceName");

In addition, user can specify the instance target state. For example, if user want to run the Task on “Master” state instance, setTargetPartitionState method can help to set the partition to assign to specific instance.

myJobCfgBuilder.setTargetPartitionState(Arrays.asList(new String[]{"Master", "Slave"}));

Instance Group

Grouping jobs with targeted group of instances feature has been supported. User firstly have to define the instance group tag for instances, which means label some instances with specific tag. Then user can put those tags to a job that only would like to assigned to those instances. For example, customer data only available on instance 1, 2, 3. These three instances can be tagged as “CUSTOMER” and customer data related jobs can set the instance group tag “CUSTOMER”. Thus customer data related jobs will only assign to instance 1, 2, 3. To add instance group tag, just set it in JobConfig.Builder:

jobCfg.setInstanceGroupTag("INSTANCEGROUPTAG");

Delayed scheduling job

Set up a schedule plan for the job. If both items are set, Helix will calculate and use the later one.

myJobCfgBuilder.setExecutionDelay(delayMs);
myJobCfgBuilder.setExecutionStart(startTimeMs);

Note that the scheduled job needs to be runnable first. Then Helix will start checking it's configuration for scheduling. If any parent jobs are not finished, the job won't be scheduled even the scheduled timestamp has already passed.

Additional Job Options

Task framework monitoring metrics

Please refer to following links.

• Job Monitor
• Workflow Monitor