I am trying to follow the intro to sub-flow results passing and for some reason, the get_task_run_results task get stack. I am using prefect server and have kubernetes agent (though I am not sure that matter since I use the --execute cli arg.

You can find one example and more info about it here. If this doesn’t help you and you’re still stuck, can you share your flow so that we can check together what’s wrong in your setup?

I see in the log:

(venv) tomercagan@Tomers-MacBook-Pro prefect-play % prefect run --name "parent" --execute
Looking up flow metadata... Done
Creating run for flow 'parent'... Done
└── Name: classy-piculet
└── UUID: 10ea2885-93c6-4ca9-9053-9770ed0b4ae0
└── Labels: ['agentless-run-b8b53ae8']
└── Parameters: {}
└── Context: {}
└── URL: <http://localhost:8080/default/flow-run/10ea2885-93c6-4ca9-9053-9770ed0b4ae0>
Executing flow run...
└── 15:18:10 | INFO    | Creating subprocess to execute flow run...
└── 15:18:10 | INFO    | Beginning Flow run for 'parent'
└── 15:18:11 | INFO    | Task 'create_flow_run': Starting task run...
└── 15:18:11 | INFO    | Creating flow run 'classy-piculet-child' for flow 'child'...
└── 15:18:11 | INFO    | Created flow run 'classy-piculet-child': <http://localhost:8080/default/flow-run/595921bf-7b99-406f-b71a-89e99c35797b>
└── 15:18:11 | INFO    | Task 'create_flow_run': Finished task run for task with final state: 'Success'
└── 15:18:11 | INFO    | Task 'get_task_run_result': Starting task run...

and it gets stack there for a while. Eventually I am getting this:

└── 14:52:21 | ERROR   | Task 'get_task_run_result': Exception encountered during task execution!
Traceback (most recent call last):
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/urllib3/connectionpool.py", line 703, in urlopen
    httplib_response = self._make_request(
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/urllib3/connectionpool.py", line 449, in _make_request
    six.raise_from(e, None)
  File "<string>", line 3, in raise_from
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/urllib3/connectionpool.py", line 444, in _make_request
    httplib_response = conn.getresponse()
  File "/usr/local/Cellar/python@3.9/3.9.10/Frameworks/Python.framework/Versions/3.9/lib/python3.9/http/client.py", line 1377, in getresponse
    response.begin()
  File "/usr/local/Cellar/python@3.9/3.9.10/Frameworks/Python.framework/Versions/3.9/lib/python3.9/http/client.py", line 320, in begin
    version, status, reason = self._read_status()
  File "/usr/local/Cellar/python@3.9/3.9.10/Frameworks/Python.framework/Versions/3.9/lib/python3.9/http/client.py", line 281, in _read_status
    line = str(self.fp.readline(_MAXLINE + 1), "iso-8859-1")
  File "/usr/local/Cellar/python@3.9/3.9.10/Frameworks/Python.framework/Versions/3.9/lib/python3.9/socket.py", line 704, in readinto
    return self._sock.recv_into(b)
ConnectionResetError: [Errno 54] Connection reset by peer

During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/requests/adapters.py", line 440, in send
    resp = conn.urlopen(
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/urllib3/connectionpool.py", line 785, in urlopen
    retries = retries.increment(
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/urllib3/util/retry.py", line 550, in increment
    raise six.reraise(type(error), error, _stacktrace)
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/urllib3/packages/six.py", line 769, in reraise
    raise value.with_traceback(tb)
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/urllib3/connectionpool.py", line 703, in urlopen
    httplib_response = self._make_request(
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/urllib3/connectionpool.py", line 449, in _make_request
    six.raise_from(e, None)
  File "<string>", line 3, in raise_from
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/urllib3/connectionpool.py", line 444, in _make_request
    httplib_response = conn.getresponse()
  File "/usr/local/Cellar/python@3.9/3.9.10/Frameworks/Python.framework/Versions/3.9/lib/python3.9/http/client.py", line 1377, in getresponse
    response.begin()
  File "/usr/local/Cellar/python@3.9/3.9.10/Frameworks/Python.framework/Versions/3.9/lib/python3.9/http/client.py", line 320, in begin
    version, status, reason = self._read_status()
  File "/usr/local/Cellar/python@3.9/3.9.10/Frameworks/Python.framework/Versions/3.9/lib/python3.9/http/client.py", line 281, in _read_status
    line = str(self.fp.readline(_MAXLINE + 1), "iso-8859-1")
  File "/usr/local/Cellar/python@3.9/3.9.10/Frameworks/Python.framework/Versions/3.9/lib/python3.9/socket.py", line 704, in readinto
    return self._sock.recv_into(b)
urllib3.exceptions.ProtocolError: ('Connection aborted.', ConnectionResetError(54, 'Connection reset by peer'))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/prefect/engine/task_runner.py", line 876, in get_task_run_state
    value = prefect.utilities.executors.run_task_with_timeout(
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/prefect/utilities/executors.py", line 468, in run_task_with_timeout
    return task.run(*args, **kwargs)  # type: ignore
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/prefect/tasks/prefect/flow_run.py", line 223, in get_task_run_result
    flow_run = flow_run.get_latest()
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/prefect/backend/flow_run.py", line 414, in get_latest
    return self.from_flow_run_id(
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/prefect/backend/flow_run.py", line 566, in from_flow_run_id
    flow_run_data = cls._query_for_flow_run(where={"id": {"_eq": flow_run_id}})
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/prefect/backend/flow_run.py", line 608, in _query_for_flow_run
    result = client.graphql(flow_run_query)
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/prefect/client/client.py", line 452, in graphql
    result = <http://self.post|self.post>(
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/prefect/client/client.py", line 407, in post
    response = self._request(
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/prefect/client/client.py", line 641, in _request
    response = self._send_request(
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/prefect/client/client.py", line 506, in _send_request
    response = <http://session.post|session.post>(
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/requests/sessions.py", line 577, in post
    return self.request('POST', url, data=data, json=json, **kwargs)
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/requests/sessions.py", line 529, in request
    resp = self.send(prep, **send_kwargs)
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/requests/sessions.py", line 645, in send
    r = adapter.send(request, **kwargs)
  File "/Users/tomercagan/dev/venv/lib/python3.9/site-packages/requests/adapters.py", line 501, in send
    raise ConnectionError(err, request=request)
requests.exceptions.ConnectionError: ('Connection aborted.', ConnectionResetError(54, 'Connection reset by peer'))
└── 14:52:24 | ERROR   | Failed to set task state with error: ConnectionError(ProtocolError('Connection aborted.', ConnectionResetError(54, 'Connection reset by peer')))

And this continues on and on

this error suggests some API or networking issue. Your server need to use a Prefect version which is >= Prefect version used by your agents and flow registration environment

I tried with prefect version 0.15.13 and version 2022.01.25 of the helm chart. I then removed everything, reinstalled the chart and reinstalled prefect to version 1.0.0 (I saw it was just announced 🙂 )

Based on your introduction, it looks you are just getting started with Prefect. We recommend using Prefect Cloud at first, since it’s much easier than using Server. Server adds a lot of additional complexity that you need to manage and Cloud is free to use for 20,000 task runs each month and you don’t even need to give your credit card details when signing up for the free Starter or Standard account. You can always deploy your own Server later, but to get started, I’d recommend using Cloud at first.

Thanks - I will try cloud and will see I didn't miss anything in the getting started guide

If you use --execute, you are triggering the so called "agentless" flow run. Check out this excellent blog post, it explains it really well (it still totally applies in Prefect 1.0, not just in 0.15.0)

I read it. I am not sure how this applies to the scenario of having a child flow - I was inspecting it and didn't find the labels I was expecting. I would expect that if I am starting an agentless execution, I will not need any agent but I am not sure this is the case (is there a bug when running parent-child flows with agentless exec?!)

Agentless execution is for a single ad-hoc flow run, so it won't work for running subflows. For that, you need to have an agent running and the proper agent label set on your flow's run config.

I was trying to use agentless to see how it works. It is worth noting that this is not possible in relevant docs 🙂

Yeah I see it mentioned here https://docs.prefect.io/orchestration/faq/upgrading_1.0.html#running-flows and here https://docs.prefect.io/orchestration/flow-runs/creation.html#cli - if you feel like we can mention it somewhere else, we are happy to accept a docs PR 🙏

In the former the

--execute

is described, and in the latter, there is a box talking about agentless running ("Agentless flow run execution") - maybe there would be a good place to mention that calling a sub-flow with local execution would not work?

I see, that's a good point, we can definitely add it as a comment - happy to review a PR if you would want to add it to the docs otherwise let me open an issue for now

That's a cool feature!