The failure task feature enables you to designate a specific task to execute in the event of a failure within your workflow. This is useful when you want to handle a failure in a specific way, such as retrying the task or sending an email notification or cleaning up the resources after a failure.
Important Note: Failure task or function accepts an optional err parameter which is an instance of FlyteError. To use the FlyteError, you will need the truefoundry version to be greater than or equal to 0.9.1 and the name of the parameter should be err only.

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How to use Failure Task/Node

  • let’s say we have a workflow with a task that fails
import typing
from truefoundry.workflow import (
    PythonTaskConfig,
    TaskPythonBuild,
    task,
    workflow,
    FlyteError,
)

task_config = PythonTaskConfig(
    image=TaskPythonBuild(
        pip_packages=["truefoundry[workflow]==0.9.1"],
    ),
)


@task(task_config=task_config)
def normal_task(param_1: str):
    print(f"param_1: {param_1}")
    raise Exception("This task will fail")

@task(task_config=task_config)
def failure_task(param_1: str, param_2: str, err: typing.Optional[FlyteError] = None):
    print(f"param_1: {param_1}")
    print(f"param_2: {param_2}")
    print(f"error: {err.message}")
    print("This task will be executed in the event of a failure")

@workflow(on_failure=failure_task)
def my_workflow(param_1: str, param_2: str):
    normal_task(param_1)
  • In the above example, we have defined two task functions normal_task and failure_task. One is a normal task that will fail and the other is a failure task that will be executed in the event of a failure.
The failure task function input parameters should be completely same as the workflow function parameters else it will raise an error.
  • Failure task function also accepts an optional err parameter which is an instance of FlyteError which you can import from truefoundry.workflow and this will contain the error message or stack trace of the failure.
  • So this workflow will execute the normal_task and if it fails, the failure_task will be executed
In this way you can handle the failure of a task in a workflow.