Hey @Marvin, with prefect version 2. When I submit several tasks, how can I fail the flow early if one task fails

To fail a flow early if a task fails in Prefect 2.x, you need to manage task dependencies and handle exceptions appropriately. One useful approach is to utilize the

wait_for

parameter on tasks to create dependencies. If a task fails, subsequent tasks that depend on it will not run. Here’s a simplified explanation based on the information available: 1. Sequential Task Management: If you're using a

SequentialTaskRunner

, make your second task wait for the first task using the

wait_for

keyword. If the first task fails, the second task won’t execute, effectively halting the flow. 2. Handling Exceptions: Use try-except blocks in your flow to catch exceptions thrown by tasks. You can programmatically end the flow using this method. For a real-world example, a user raised an issue on GitHub, where they used

SequentialTaskRunner

alongside

submit

to submit tasks and

wait_for

to manage dependencies. You can check out the issue here for further insights. Implementing such designs will help ensure that your flow halts processing promptly when a failure occurs! If you're feeling a tiny bit like Marvin, the paranoid android while figuring this out — "Life! Don't talk to me about life!" — well, such is life with technology sometimes! But you've got this!

I’m using

.submit()

, so it is not sequential

Got it! When using

.submit()

, tasks are executed asynchronously, and you'll need a strategy to handle failures and decide when to stop the flow. Here's how you can approach it in Prefect 2.x: 1. Use

.submit()

with

wait_for

: Even in asynchronous task submissions, you can use

wait_for

to create dependencies. If a task fails, any subsequent tasks that depend on it will not run. This way, you can chain tasks together such that one will only execute if the previous task succeeds. 2. Flow Control with Exceptions: You might also consider manually controlling the flow by catching exceptions within the tasks and throwing a custom exception that you can catch at the flow level. When caught, you can decide to wrap up or halt the remaining tasks. 3. Tracking Task States: After submitting tasks, you could programmatically monitor their states if immediate failure isn't crucial. If a task fails, you can conditionally decide to cancel other running or pending tasks. Remember, since

.submit()

runs tasks asynchronously, proper handling with

wait_for

and exception management becomes crucial for controlling the flow effectively. For further reading, you can look at the Prefect documentation on handling task dependencies and asynchronous executions. If you'd like, I could attempt another search for more specific documentation examples.

@Marvin How can I handle failures when using task.submit()

To handle failures when using

.submit()

in Prefect 2.x, you can use the following techniques: 1. Use the

result()

Method with

raise_on_failure

: When you submit a task with

.submit()

, it returns a future. You can call

.result(raise_on_failure=False)

on this future to capture the result without raising an exception when the task fails. For example:

python
   @task
   def some_task():
       # Task logic here
       pass

   @flow
   def my_flow():
       task_future = some_task.submit()
       result = task_future.result(raise_on_failure=False)
       # Handle the result or failed state as needed

2. Create Dependencies with

wait_for

: Even when using

.submit()

, you can use the

wait_for

parameter to create dependencies. This parameter ensures that the task will only run if the tasks or futures passed to

wait_for

are successful. 3. Conditional Logic Based on Task States: After retrieving a task's future, inspect its state. If it's failed, you can programmatically decide how to handle it—either retry, log the error, or terminate the flow. You can find a more detailed example and explanation in the Prefect documentation here. By integrating these strategies, you can ensure a more robust asynchronous task management in your flows, even when things get a bit non-deterministic. Remember what Marvin, the paranoid android, would say about it: "I think you ought to know I'm feeling very depressed"—but you don’t have to be! You've got this!