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Has anyone seen an issue with Dask workers having ...
# prefect-server
g
Has anyone seen an issue with Dask workers having errors around serialization? I'm submitting a flow from a client (simple hello world) -> prefect server on an ec2 instance -> prefect agent -> Dask scheduler -> Dask workers. Everything is flowing allthe way to the worker, but then I am seeing a 
TypeError: can not serialize 'Variable' object
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==> prefect_logs/dask_worker.log <==
distributed.protocol.core - CRITICAL - Failed to Serialize
Traceback (most recent call last):
  File "/opt/conda/lib/python3.7/site-packages/distributed/protocol/core.py", line 25, in dumps
    small_header, small_payload = dumps_msgpack(msg)
  File "/opt/conda/lib/python3.7/site-packages/distributed/protocol/core.py", line 163, in dumps_msgpack
    payload = msgpack.dumps(msg, use_bin_type=True)
  File "/opt/conda/lib/python3.7/site-packages/msgpack/__init__.py", line 35, in packb
    return Packer(**kwargs).pack(o)
  File "msgpack/_packer.pyx", line 286, in msgpack._cmsgpack.Packer.pack
  File "msgpack/_packer.pyx", line 292, in msgpack._cmsgpack.Packer.pack
  File "msgpack/_packer.pyx", line 289, in msgpack._cmsgpack.Packer.pack
  File "msgpack/_packer.pyx", line 225, in msgpack._cmsgpack.Packer._pack
  File "msgpack/_packer.pyx", line 283, in msgpack._cmsgpack.Packer._pack
TypeError: can not serialize 'Variable' object
distributed.comm.utils - INFO - Unserializable Message: {'op': 'variable_get', 'timeout': 0, 'name': <distributed.variable.Variable object at 0x7fec9eafaef0>, 'client': 'Client-worker-365168fe-ccf9-11ea-800b-0242ac110004', 'reply': True}
distributed.comm.utils - ERROR - can not serialize 'Variable' object
Traceback (most recent call last):
  File "/opt/conda/lib/python3.7/site-packages/distributed/comm/utils.py", line 35, in _to_frames
    msg, serializers=serializers, on_error=on_error, context=context
  File "/opt/conda/lib/python3.7/site-packages/distributed/protocol/core.py", line 25, in dumps
    small_header, small_payload = dumps_msgpack(msg)
  File "/opt/conda/lib/python3.7/site-packages/distributed/protocol/core.py", line 163, in dumps_msgpack
    payload = msgpack.dumps(msg, use_bin_type=True)
  File "/opt/conda/lib/python3.7/site-packages/msgpack/__init__.py", line 35, in packb
    return Packer(**kwargs).pack(o)
  File "msgpack/_packer.pyx", line 286, in msgpack._cmsgpack.Packer.pack
  File "msgpack/_packer.pyx", line 292, in msgpack._cmsgpack.Packer.pack
  File "msgpack/_packer.pyx", line 289, in msgpack._cmsgpack.Packer.pack
  File "msgpack/_packer.pyx", line 225, in msgpack._cmsgpack.Packer._pack
  File "msgpack/_packer.pyx", line 283, in msgpack._cmsgpack.Packer._pack
TypeError: can not serialize 'Variable' object
d
Hey @Greg Desmarais! Would you mind sharing your flow?
I will see if I can help or direct you to our resident Dask expert who almost certainly can 😄
l
Copy code
Unserializable Message: {'op': 'variable_get', 'timeout': 0, 'name': <distributed.variable.Variable object at 0x7fec9eafaef0>, 'client': 'Client-worker-365168fe-ccf9-11ea-800b-0242ac110004', 'reply': True}
that part reveals that you try to send not serializable object distributed.variable.Variable as a json
maybe just extract a string representation?
g
Flow on the way...
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@task
def say_hello():
    return f'done'

with Flow("Dask ECS Test 2") as flow:
    say_hello()
Simple enough?
😉
Then,
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bucket = 'celsius-temp-data'
key = 'datasciences/prefect_flows/dask_ecs_flow_test_2'
flow.storage = S3(bucket, key=key)
labels = ['size-small']
executor = DaskExecutor(address=f'{PREFECT_COMPOSE_HOST}:38786') 
flow.environment = LocalEnvironment(executor=executor, labels=labels)
flow_id = flow.register(labels=labels)
p_client = Client()
ret = p_client.create_flow_run(flow_id=flow_id)
print(f'Created flow run: {ret}')
👀 1
I had some fargate cruft from previous efforts...
Also - the stack trace above isn't from my code - it is inside the dask stuff. I don't sall any of those ops directly.
d
Looks like this was fixed recently! What version of Prefect are you using?
g
You are probably going to laugh a bit. In between the writing of this original posting and now, my pycharm told me there was an update to prefect - I was on 0.12.4. I went through the change logs and found that exact issue. I am about to kick off a re-build of all my images and the like to go to 0.12.5.
In reading through the fix, I'm not sure how it addresses the issue, but there is a lot of magic going on, and it certainly is in the right arena. I'll upgrade then post back here.
d
Great! 😄
g
I was pretty sure I had searched the issues on github, but maybe not. It also looks like this pr might not be tied to an issue?
Oh - and the pr refers to an issue reported on slack...which was me 😉 :snake eating tail:
😂 2
Ok - after upgrading all over the place, you can consider the case closed! Got a nice setup working now...Thanks!
d
You’re welcome! Glad it all worked out 😄
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