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Task Definition

Task Definitions are used to register CUSTOM tasks (workers). Conductor maintains a registry of user task types. A task type MUST be registered before being used in a workflow.

This should not be confused with Task Configurations which are part of the Workflow Definition, and are iterated in the tasks property in the definition.

Schema

Field Type Description Notes
name string Task Name. Unique name of the Task that resonates with its function. Must be unique
description string Description of the task Optional
retryCount number Number of retries to attempt when a Task is marked as failure Defaults to 3 with maximum allowed capped at 10
retryLogic string (enum) Mechanism for the retries See Retry Logic
retryDelaySeconds number Time to wait before retries Defaults to 60 seconds
timeoutPolicy string (enum) Task's timeout policy Defaults to TIME_OUT_WF; See Timeout Policy
timeoutSeconds number 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
responseTimeoutSeconds number If greater than 0, 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
pollTimeoutSeconds number Time in seconds, after which the task is marked as TIMED_OUT if not polled by a worker No timeouts if set to 0
inputKeys array of string(s) Array of keys of task's expected input. Used for documenting task's input. Optional. See Using inputKeys and outputKeys.
outputKeys array of string(s) Array of keys of task's expected output. Used for documenting task's output. Optional. See Using inputKeys and outputKeys.
inputTemplate object Define default input values. Optional. See Using inputTemplate
concurrentExecLimit number Number of tasks that can be executed at any given time Optional
rateLimitFrequencyInSeconds number Sets the rate limit frequency window. Optional. See Task Rate limits
rateLimitPerFrequency number Sets the max number of tasks that can be given to workers within window. Optional. See Task Rate limits below
ownerEmail string Email address of the team that owns the task Required

Retry Logic

  • FIXED: Reschedule the task after retryDelaySeconds
  • EXPONENTIAL_BACKOFF: Reschedule the task after retryDelaySeconds * (2 ^ attemptNumber)
  • LINEAR_BACKOFF: Reschedule after retryDelaySeconds * backoffRate * attemptNumber

Timeout Policy

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

Task Concurrent Execution Limits

concurrentExecLimit limits the number of simultaneous Task executions at any point.

Example 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

Rate Limiting

Rate limiting is only supported for the Redis-persistence module and is not available with other persistence layers.

  • 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". No rate limit if set to 0.

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.

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}"
}

Complete Example

This is an example of a Task Definition for a worker implementation named encode_task.

{
  "name": "encode_task",
  "retryCount": 3,
  "timeoutSeconds": 1200,
  "inputKeys": [
    "sourceRequestId",
    "qcElementType"
  ],
  "outputKeys": [
    "state",
    "skipped",
    "result"
  ],
  "timeoutPolicy": "TIME_OUT_WF",
  "retryLogic": "FIXED",
  "retryDelaySeconds": 600,
  "responseTimeoutSeconds": 3600,
  "pollTimeoutSeconds": 3600,
  "concurrentExecLimit": 100,
  "rateLimitFrequencyInSeconds": 60,
  "rateLimitPerFrequency": 50,
  "ownerEmail": "foo@bar.com",
  "description": "Sample Encoding task"
}