Task Definition

Conductor maintains a registry of worker tasks. A task MUST be registered before being used in a workflow.

Example

{
  "name": "encode_task",
  "retryCount": 3,

  "timeoutSeconds": 1200,
  "pollTimeoutSeconds": 3600,
  "inputKeys": [
    "sourceRequestId",
    "qcElementType"
  ],
  "outputKeys": [
    "state",
    "skipped",
    "result"
  ],
  "timeoutPolicy": "TIME_OUT_WF",
  "retryLogic": "FIXED",
  "retryDelaySeconds": 600,
  "responseTimeoutSeconds": 1200,
  "concurrentExecLimit": 100,
  "rateLimitFrequencyInSeconds": 60,
  "rateLimitPerFrequency": 50,
  "ownerEmail": "foo@bar.com",
  "description": "Sample Encoding task"
}
field description Notes
name Task Type. Unique name of the Task that resonates with it's function. Unique
description Description of the task optional
retryCount No. of retries to attempt when a Task is marked as failure defaults to 3
retryLogic Mechanism for the retries see possible values below
retryDelaySeconds Time to wait before retries defaults to 60 seconds
timeoutPolicy Task's timeout policy see possible values below
timeoutSeconds Time in seconds, after which the task is marked as TIMED_OUT if not completed after transitioning to IN_PROGRESS status for the first time No timeouts if set to 0
pollTimeoutSeconds Time in seconds, after which the task is marked as TIMED_OUT if not polled by a worker No timeouts if set to 0
responseTimeoutSeconds Must be greater than 0 and less than timeoutSeconds. The task is rescheduled if not updated with a status after this time (heartbeat mechanism). Useful when the worker polls for the task but fails to complete due to errors/network failure. defaults to 3600
inputKeys Array of keys of task's expected input. Used for documenting task's input. See Using inputKeys and outputKeys. optional
outputKeys Array of keys of task's expected output. Used for documenting task's output optional
inputTemplate See Using inputTemplate below. optional
concurrentExecLimit Number of tasks that can be executed at any given time. optional
rateLimitFrequencyInSeconds, rateLimitPerFrequency See Task Rate limits below. optional

Retry Logic

  • FIXED : Reschedule the task after the retryDelaySeconds
  • EXPONENTIAL_BACKOFF : Reschedule after retryDelaySeconds * attemptNumber

Timeout Policy

  • RETRY : Retries the task again
  • TIME_OUT_WF : Workflow is marked as TIMED_OUT and terminated
  • ALERT_ONLY : Registers a counter (task_timeout)

Task Concurrent Execution Limits

  • concurrentExecLimit limits the number of simultaneous Task executions at any point.
    Example:
    If you have 1000 task executions waiting in the queue, and 1000 workers polling this queue for tasks, but if you have set concurrentExecLimit to 10, only 10 tasks would be given to workers (which would lead to starvation). If any of the workers finishes execution, a new task(s) will be removed from the queue, while still keeping the current execution count to 10.

Task Rate limits

  • rateLimitFrequencyInSeconds and rateLimitPerFrequency should be used together.
  • rateLimitFrequencyInSeconds sets the "frequency window", i.e the duration to be used in events per duration. Eg: 1s, 5s, 60s, 300s etc.
  • rateLimitPerFrequencydefines the number of Tasks that can be given to Workers per given "frequency window".
    Example:
    Let's set rateLimitFrequencyInSeconds = 5, and rateLimitPerFrequency = 12. This means, our frequency window is of 5 seconds duration, and for each frequency window, Conductor would only give 12 tasks to workers. So, in a given minute, Conductor would only give 12*(60/5) = 144 tasks to workers irrespective of the number of workers that are polling for the task.
    Note that unlike concurrentExecLimit, rate limiting doesn't take into account tasks already in progress/completed. Even if all the previous tasks are executed within 1 sec, or would take a few days, the new tasks are still given to workers at configured frequency, 144 tasks per minute in above example.
    Note: Rate limiting is only supported for the Redis-persistence module and is not available with other persistence layers.

Using inputKeys and outputKeys

  • inputKeys and outputKeys can be considered as parameters and return values for the Task.
  • Consider the task Definition as being represented by an interface: (value1, value2 .. valueN) someTaskDefinition(key1, key2 .. keyN);
  • However, these parameters are not strictly enforced at the moment. Both inputKeys and outputKeys act as a documentation for task re-use. The tasks in workflow need not define all of the keys in the task definition.
  • In the future, this can be extended to be a strict template that all task implementations must adhere to, just like interfaces in programming languages.

Using inputTemplate

  • inputTemplate allows to define default values, which can be overridden by values provided in Workflow.
  • Eg: In your Task Definition, you can define your inputTemplate as:
"inputTemplate": {
    "url": "https://some_url:7004"
}
  • Now, in your workflow Definition, when using above task, you can use the default url or override with something else in the task's inputParameters.
"inputParameters": {
    "url": "${workflow.input.some_new_url}"
}