Task Definition

Task Definitions are used to register SIMPLE 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

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

!!! note "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 or a terminal state. 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": "[email protected]",
  "description": "Sample Encoding task"
}