Error while initializing Ray on an EC2 master node - python-3.x

Question

I am using Ray to run a parallel loop on an Ubuntu 14.04 cluster on AWS EC2. The following Python 3 script works well on my local machine with just 4 workers (imports and local initializations left out):-
ray.init() #initialize Ray
#ray.remote
def test_loop(n):
c=tests[n,0]
tout=100
rc=-1
with tmp.TemporaryDirectory() as path: #Create a temporary directory
for files in filelist: #then copy in all of the
sh.copy(filelist,path) #files
txtfile=path+'/inputf.txt' #create the external
fileId=open(txtfile,'w') #data input text file,
s='Number = '+str(c)+"\n" #write test number,
fileId.write(s)
fileId.close() #close external parameter file,
os.chdir(path) #and change working directory
try: #Try running simulation:
rc=sp.call('./simulation.run',timeout=tout,stdout=sp.DEVNULL,\
stderr=sp.DEVNULL,shell=True) #(must use .call for timeout)
outdat=sio.loadmat('outputf.dat') #get the output data struct
rt_Data=outdat.get('rt_Data') #extract simulation output
err=float(rt_Data[-1]) #use final value of error
except: #If system fails to execute,
err=deferr #use failure default
#end try
if (err<=0) or (err>deferr) or (rc!=0):
err=deferr #Catch other types of failure
return err
if __name__=='__main__':
result=ray.get([test_loop.remote(n) for n in range(0,ntest)])
print(result)
The unusual bit here is that the simulation.run has to read in a different test number from an external text file when it runs. The file name is the same for all iterations of the loop, but the test number is different.
I launched an EC2 cluster using Ray, with the number of CPUs available equal to n (I am trusting that Ray will not default to multi-threading). Then I had to copy the filelist (which includes the Python script) from my local machine to the master node using rsync, because I couldn't do this from the config (see recent question: "Workers not being launched on EC2 by Ray"). Then ssh into that node, and run the script. The result is a file-finding error:-
~$ python3 test_small.py
2019-04-29 23:39:27,065 WARNING worker.py:1337 -- WARNING: Not updating worker name since `setproctitle` is not installed. Install this with `pip install setproctitle` (or ray[debug]) to enable monitoring of worker processes.
2019-04-29 23:39:27,065 INFO node.py:469 -- Process STDOUT and STDERR is being redirected to /tmp/ray/session_2019-04-29_23-39-27_3897/logs.
2019-04-29 23:39:27,172 INFO services.py:407 -- Waiting for redis server at 127.0.0.1:42930 to respond...
2019-04-29 23:39:27,281 INFO services.py:407 -- Waiting for redis server at 127.0.0.1:47779 to respond...
2019-04-29 23:39:27,282 INFO services.py:804 -- Starting Redis shard with 0.21 GB max memory.
2019-04-29 23:39:27,296 INFO node.py:483 -- Process STDOUT and STDERR is being redirected to /tmp/ray/session_2019-04-29_23-39-27_3897/logs.
2019-04-29 23:39:27,296 INFO services.py:1427 -- Starting the Plasma object store with 0.31 GB memory using /dev/shm.
(pid=3917) sh: 0: getcwd() failed: No such file or directory
2019-04-29 23:39:44,960 ERROR worker.py:1672 -- Traceback (most recent call last):
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/ray/worker.py", line 909, in _process_task
self._store_outputs_in_object_store(return_object_ids, outputs)
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/ray/worker.py", line 820, in _store_outputs_in_object_store
self.put_object(object_ids[i], outputs[i])
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/ray/worker.py", line 375, in put_object
self.store_and_register(object_id, value)
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/ray/worker.py", line 309, in store_and_register
self.task_driver_id))
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/ray/worker.py", line 238, in get_serialization_context
_initialize_serialization(driver_id)
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/ray/worker.py", line 1148, in _initialize_serialization
serialization_context = pyarrow.default_serialization_context()
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/ray/pyarrow_files/pyarrow/serialization.py", line 326, in default_serialization_context
register_default_serialization_handlers(context)
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/ray/pyarrow_files/pyarrow/serialization.py", line 321, in register_default_serialization_handlers
_register_custom_pandas_handlers(serialization_context)
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/ray/pyarrow_files/pyarrow/serialization.py", line 129, in _register_custom_pandas_handlers
import pandas as pd
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/pandas/__init__.py", line 42, in <module>
from pandas.core.api import *
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/pandas/core/api.py", line 10, in <module>
from pandas.core.groupby import Grouper
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/pandas/core/groupby.py", line 49, in <module>
from pandas.core.frame import DataFrame
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/pandas/core/frame.py", line 74, in <module>
from pandas.core.series import Series
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/pandas/core/series.py", line 3042, in <module>
import pandas.plotting._core as _gfx # noqa
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/pandas/plotting/__init__.py", line 8, in <module>
from pandas.plotting import _converter
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/pandas/plotting/_converter.py", line 7, in <module>
import matplotlib.units as units
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/matplotlib/__init__.py", line 1060, in <module>
rcParams = rc_params()
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/matplotlib/__init__.py", line 892, in rc_params
fname = matplotlib_fname()
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/matplotlib/__init__.py", line 736, in matplotlib_fname
for fname in gen_candidates():
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/matplotlib/__init__.py", line 725, in gen_candidates
yield os.path.join(six.moves.getcwd(), 'matplotlibrc')
FileNotFoundError: [Errno 2] No such file or directory
During handling of the above exception, another exception occurred:
The problem then seems to repeat for all the other workers and finally gives up:-
AttributeError: module 'pandas' has no attribute 'core'
This error is unexpected and should not have happened. Somehow a worker
crashed in an unanticipated way causing the main_loop to throw an exception,
which is being caught in "python/ray/workers/default_worker.py".
2019-04-29 23:44:08,489 ERROR worker.py:1672 -- A worker died or was killed while executing task 000000002d95245f833cdbf259672412d8455d89.
Traceback (most recent call last):
File "test_small.py", line 82, in <module>
result=ray.get([test_loop.remote(n) for n in range(0,ntest)])
File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/ray/worker.py", line 2184, in get
raise value
ray.exceptions.RayWorkerError: The worker died unexpectedly while executing this task.
I suspect that I am not initializing Ray correctly. I tried with ray.init(redis_address="172.31.50.149:6379") - which was the redis address given when the cluster was formed, but the error was more or less the same. I also tried starting Ray on the master (in case it needed starting):-
~$ ray start --redis-address 172.31.50.149:6379 #Start Ray
2019-04-29 23:46:20,774 INFO services.py:407 -- Waiting for redis server at 172.31.50.149:6379 to respond...
2019-04-29 23:48:29,076 INFO services.py:412 -- Failed to connect to the redis server, retrying.
....etc.

Answer 1

The installation of pandas and matplotlib on the master node seems to have solved the problem. Ray now initializes successfully.