Hi all, I am experimenting with nested tasks and the UI appears to just show the parent task as an isolated rectangle with no dependency or encapsulation of its child tasks. Is this expected behavior or am I doing something wrong? I was hoping for it to enclose the child tasks the way that sub-flows do.

Hey Daniel, We just did a quick test internally and we're seeing nested tasks encapsulated by their parent as we expect. Can you share a brief MRE (minimum reproducible example) along with your Prefect version & any other pertinent environment info?

Certainly. Flow and deployment code below. Server is hosted on K8s and is

2.19.8

. Result of running the deployment in the UI is attached as image. Python file for flow tasks:

from prefect import flow, get_run_logger, deploy
from prefect.deployments import DeploymentImage
from prefect import task


@task(log_prints=True)
def child_task():
    print("I am a child task")


@task(log_prints=True)
def parent_task():
    print("I am a parent task")
    return child_task()


@flow()
def test_flow_nested_task_mre():
    return parent_task()


if __name__ == "__main__":
    deployment_container_image = DeploymentImage(
        name="{registry remove for confidentiality}/prefect-test-flow-nested-task-mre",
        tag="latest",
        dockerfile="Dockerfile",
        platform="linux/amd64",
    )

    test_flow_nested_task_mre.deploy(
        name=f"test-flow-nested-task-mre-primary",
        work_pool_name="default",
        image=deployment_container_image,
    )

Dockerfile:

FROM prefecthq/prefect:2.20.10-python3.11
COPY requirements.txt /opt/prefect/prefect/requirements.txt
# Hotfix for oscrypto openssl bug (<https://community.snowflake.com/s/question/0D5Do000010NAVzKAO/hi-snowflake-teami-am-facing-issues-while-connecting-to-snowflake-using-snowflake-connector-with-oscryptoerrorslibrarynotfounderror-error-detecting-the-version-of-libcrypto>)
RUN python -m pip install oscrypto@git+https://github.com/wbond/oscrypto.git@d5f3437ed24257895ae1edd9e503cfb352e635a8
RUN python -m pip install -v -r /opt/prefect/prefect/requirements.txt
COPY . /opt/prefect/prefect/
WORKDIR /opt/prefect/prefect/

Requirements.txt

prefect>=2.17.1,<3.0.0
prefect-dbt>=0.4.1,<1.0.0
prefect-snowflake>=0.27.3,<1.0.0
dbt-core>=1.8.6,<2.0.0
dbt-snowflake>=1.8.3,<2.0.0
pygit2>=1.14.1,<2.0.0
azure-identity>=1.16.0,<2.0.0
azure-keyvault-secrets>=4.8.0,<5.0.0
msal>=1.28.0,<2.0.0
snowflake-connector-python>=3.8.1,<4.0.0
html-to-json>=2.0.0,<3.0.0
cryptography>=42.0.5,<43.0.0
black>=24.4.0,<25.0.0

Result in the UI:

This is a great MRE! Thanks for being so thorough 💯

.00

@Dylan After upgrading to prefect 3 nested tasks in my MRE are rendering correctly. Unfortunately they are still rendering as separate unassociated entities in my production code. I am having a difficult time re-producing this in an MRE. Any chance we could connect on this?

Hey Daniel, definitely! You can connect with an engineer on our team here: https://calendly.com/prefect-experts/prefect-product-advocates?month=2024-11

I figured it out. The UI stops nesting child tasks if the parent task has more than one argument. For example, it stops working with the below modifications to the previous mre. If you remove

test_arg_2

the UI renders it as a nested task again.

from prefect import flow, task, deploy
from prefect.docker.docker_image import DockerImage


@task(log_prints=True)
def child_task():
    print("I am a child task")
    return 1


@task(log_prints=True)
def parent_task(test_arg, test_arg_2):
    print("I am a parent task")
    result = child_task()
    print(result)
    return result


@flow()
def test_flow_nested_task_mre():
    result = parent_task(
        test_arg="hello",
        test_arg_2="world",
    )
    return result


if __name__ == "__main__":
    custom_docker_image = DockerImage(
        name="[REDACTED]/test-nested-tasks-mre",
        tag="latest",
        dockerfile="Dockerfile",
    )

    flow_deployment = test_flow_nested_task_mre.to_deployment(
        name=f"test-nested-tasks-mre",
    )

    deploy(
        flow_deployment,
        work_pool_name="kubernetes",
        image=custom_docker_image,
    )

That's certainly a bug! Would you mind opening an issue with the UI tag and we'll investigate 👍

Done! Though I don't think I have permissions to add labels so here it is: https://github.com/PrefectHQ/prefect/issues/15933

Thank you!

@Dylan I have subtasks that are created with task.submit that are not showing up either -- they have arguments, so probably the same bug, but thought I'd add another data point