@Marvin, do subflows inherent the task runner of the parent flow they are called from?

In Prefect, subflows do not inherit the task runner from their parent flow. Each subflow starts with its own task runner. So, if you need a specific task runner for a subflow, you'll have to explicitly define it for that subflow. Otherwise, you'll find the subflow behaving more independently, much like a teenager trying to assert their independence by picking their own path, rather than following the parents'. For more detailed information, you can check out the Prefect documentation: - Prefect 2.x Task Runners - Prefect 3.x Task Runners You can see that setting up a nested or subflow with a different task runner is a good approach for optimizing task performance, just like wearing sunglasses to look cool in photos—it's all about the right tool for the job.

@Marvin, how can I make a subflow inherent the same type of task runner as its parent ?

To make a subflow inherit the same type of task runner as its parent in Prefect, you need to explicitly set the same task runner for the subflow as used by the parent flow. Prefect, by default, doesn't make subflows automatically adopt the parent's task runner type. It's a bit like trying to get all ducks in a row; you have to specify where you want each duck to go. Here's how you can do it: 1. When you define your parent flow, note the task runner you use. 2. For the subflow, specify the same task runner explicitly in its decorator. For Prefect 2.x and 3.x, here's how you might set it:

python
from prefect import flow, task
from prefect.task_runners import SomeTaskRunner  # Replace with your desired task runner

@task
def some_task():
    print("Executing task")

@flow(task_runner=SomeTaskRunner())  # Parent flow with specific task runner
def parent_flow():
    child_flow()  # Call subflow
    some_task.submit()

@flow(task_runner=SomeTaskRunner())  # Subflow with the same task runner
def child_flow():
    some_task.submit()

if __name__ == "__main__":
    parent_flow()

For more details on this topic, you may want to peruse the official Prefect documentation: - Prefect 2.x Task Runners - Prefect 3.x Task Runners Remember, even the most autonomous subflows appreciate a little guidance from their parent flows now and again.

@Marvin, how can I create new task runners for a subflow dynamically? It seems like if I have a flow defined as

@flow(task_runner = SomeTaskRunner)
def flow1():
    print('foo')

and called with

if __name__ == "__main__":
  newflow = flow1.with_options(task_runner=ConcurrentTaskRunner())
  newflow()

the newflow still calls the task runner in the flow definition

When you want to dynamically create a new task runner for a subflow in Prefect and change it at runtime, it's essential to ensure that you're correctly using method calls designed to alter flow configurations. The issue you're encountering with using

with_options

not affecting the task runner likely stems from needing the correct method or approach for changing runtime parameters. Here's a more reliable way to dynamically specify a task runner for a subflow at runtime: 1. Use the

.with_options()

method as intended, ensuring integration with the chosen task runner. 2. Ensure your Prefect version is consistent with the features you're expecting. Some features might behave differently across versions. From the documentation insights: - Prefect allows specifying task runners dynamically; however, it requires the

task_runner

to be adjusted appropriately when creating new instances of the flows or subflows. - If the

with_options

method is not reflecting changes, you may consider creating a new instance of the flow and explicitly passing the desired task runner as an argument. Here's a typical approach in Prefect 2.x and 3.x:

python
from prefect import flow, task
from prefect.task_runners import ConcurrentTaskRunner

@task
def say_hello():
    print("Hello!")

@flow(task_runner=ConcurrentTaskRunner())
def my_flow():
    say_hello()

if __name__ == "__main__":
    my_flow_new = my_flow.with_options(task_runner=ConcurrentTaskRunner())
    my_flow_new()

If

with_options

doesn't seem effective, verifying Prefect version-specific nuances or consulting updated documentation might provide additional guidance. You can learn more about using task runners via the following resources: - Prefect 2.x Task Runners - Prefect 3.x Task Runners In the grand saga of flow orchestration, task runners are basically the underappreciated supporting actors – much needed for getting the job done, but sometimes needing a bit of prodding to perform on cue!