Dynamic

"type" : "DYNAMIC"

The DYNAMIC task allows one to execute a task whose name is resolved dynamically at run-time. The task name to execute is specified as taskToExecute in inputParameters.

Use Cases

Consider a scenario, when we have to make decision of executing a task dynamically i.e. while the workflow is still running. In such cases, Dynamic Task would be useful.

Configuration

To use the DYNAMIC task, you need to provide dynamicTaskNameParam at the top level of the task configuration, as well as an attribute in inputParameters matching the value you selected for dynamicTaskNameParam.

name	description
dynamicTaskNameParam	Name of the parameter from inputParameters whose value is used to schedule the task. e.g. "taskToExecute"

inputParameters

name	description
*dynamicTaskNameParam e.g. taskToExecute	Name of task to execute.

Example

Suppose in a workflow, we have to take decision to ship the courier with the shipping service providers on the basis of Post Code.

Consider the following 3 task definitions.

The following task shipping_info generates an output on the basis of which decision would be taken to run the next task.

{
  "name": "shipping_info",
  "retryCount": 3,
  "timeoutSeconds": 600,
  "pollTimeoutSeconds": 1200,
  "timeoutPolicy": "TIME_OUT_WF",
  "retryLogic": "FIXED",
  "retryDelaySeconds": 300,
  "responseTimeoutSeconds": 300,
  "concurrentExecLimit": 100,
  "rateLimitFrequencyInSeconds": 60,
  "ownerEmail":"abc@example.com",
  "rateLimitPerFrequency": 1
}

The following are the two custom tasks. Only one these tasks will run based on the output generated by the shipping_info task:

{
  "name": "ship_via_fedex",
  "retryCount": 3,
  "timeoutSeconds": 600,
  "pollTimeoutSeconds": 1200,
  "timeoutPolicy": "TIME_OUT_WF",
  "retryLogic": "FIXED",
  "retryDelaySeconds": 300,
  "responseTimeoutSeconds": 300,
  "concurrentExecLimit": 100,
  "rateLimitFrequencyInSeconds": 60,
  "ownerEmail":"abc@example.com",
  "rateLimitPerFrequency": 2
},
{
  "name": "ship_via_ups",
  "retryCount": 3,
  "timeoutSeconds": 600,
  "pollTimeoutSeconds": 1200,
  "timeoutPolicy": "TIME_OUT_WF",
  "retryLogic": "FIXED",
  "retryDelaySeconds": 300,
  "responseTimeoutSeconds": 300,
  "concurrentExecLimit": 100,
  "rateLimitFrequencyInSeconds": 60,
  "ownerEmail":"abc@example.com",
  "rateLimitPerFrequency": 2
}

We will create a workflow with the following definition :

{
  "name": "Shipping_Flow",
  "description": "Ships smartly on the basis of Shipping info",
  "version": 1,
  "tasks": [
    {
      "name": "shipping_info",
      "taskReferenceName": "shipping_info",
      "inputParameters": {
      },
      "type": "CUSTOM"
    },
    {
      "name": "shipping_task",
      "taskReferenceName": "shipping_task",
      "inputParameters": {
        "taskToExecute": "${shipping_info.output.shipping_service}"
      },
      "type": "DYNAMIC",
      "dynamicTaskNameParam": "taskToExecute"
    }

  ],
  "restartable": true,
  "ownerEmail":"abc@example.com",
  "workflowStatusListenerEnabled": true,
  "schemaVersion": 2
}

The workflow created is shown in the below diagram.

Note : shipping_task is a DYNAMIC task and the taskToExecute parameter can be set with input value provided while running the workflow or with the output of previous tasks.

Here, it is set to the output provided by the previous task i.e. ${shipping_info.output.shipping_service}.

If the input value is provided while running the workflow it can be accessed by ${workflow.input.shipping_service}.

{
  "shipping_service": "ship_via_fedex"
}

We can see in the below example that on the basis of Post Code the shipping service is being decided.

Based on given set of inputs i.e. Post Code starts with '9' hence, ship_via_fedex is executed -

If the Post Code startes with anything other than 9 ship_via_ups is executed -

If the incorrect task name or the task that doesn't exist is provided then the workflow fails and we get the error Invalid task specified. Cannot find task by name in the task definitions.

If null reference is provided in the task name the workflow also fails and we get the error Cannot map a dynamic task based on the parameter and input. Parameter= taskToExecute, input= {taskToExecute=null}