Python: Erratic joblib behaviour on Flask - flask

Question

I am trying to deploy a machine learning model on AWS EC2 instance using Flask. These are sklearn's fitted Random Forest models that are pickled using joblib. When I host Flask on localhost and load them into memory everything runs smoothly. However, when I deploy it on the apache2 server using mod_wsgi, joblib works sometimes(i.e. the models are loaded using joblib sometimes) and the other times the server just hangs. There is no error in logs. Any ideas would be appreciated.
Here is the relevant code that I am using:
# In[49]:
from flask import Flask, jsonify, request, render_template
from datetime import datetime
from sklearn.externals import joblib
import pickle as pkl
import os
# In[50]:
app = Flask(__name__, template_folder="/home/ubuntu/flaskapp/")
# In[51]:
log = lambda msg: app.logger.info(msg, extra={'worker_id': "request.uuid" })
# Logger
import logging
handler = logging.FileHandler('/home/ubuntu/app.log')
handler.setLevel(logging.ERROR)
app.logger.addHandler(handler)
# In[52]:
#app.route('/')
def host_template():
return render_template('Static_GUI.html')
# In[53]:
def load_models(path):
model_arr = [0]*len(os.listdir(path))
for filename in os.listdir(path):
f = open(path+"/"+filename, 'rb')
model_arr[int(filename[2:])] = joblib.load(f)
print("Classifier ", filename[2:], " added.")
f.close()
return model_arr
# In[54]:
partition_limit = 30
# In[55]:
print("Dictionaries being loaded.")
dict_file_path = "/home/ubuntu/Dictionaries/VARR"
dictionaries = pkl.load(open(dict_file_path, "rb"))
print("Dictionaries Loaded.")
# In[56]:
print("Begin loading classifiers.")
model_path = "/home/ubuntu/RF_Models/"
classifier_arr = load_models(model_path)
print("Classifiers Loaded.")
if __name__ == '__main__':
log("/home/ubuntu/print.log")
print("Starting API")
app.run(debug=True)

Answer 1

I was stuck with this for quite sometime. Posting the answer in case someone runs into this problem. Using print statements and looking at logs I narrowed the problem down to joblib.load statement. I found this awesome blog: http://blog.rtwilson.com/how-to-fix-flask-wsgi-webapp-hanging-when-importing-a-module-such-as-numpy-or-matplotlib
The idea of using a global process group fixed the problem. That forced the use of main interpreter just as the top comment on that blog page mentions.