Flask WSGI application hangs when import nltk

Question

I followed the instructions here to create a onefile flask-app deployed to apache2 with mod-wsgi on ubuntu. That all works fine when using the original flask app. However, when adding import nltk to the flask app apache hangs (no 500).

I use python 2.7 and nltk 2.0.4

Others seem to have had similar problems with other packages. Setting

WSGIApplicationGroup %{GLOBAL}

in the VirtualHost configuration seemed to have helped. However, I still get the same behavior. Did anybody run into the same issue? Thanks for the help!

Here is the VirtualHost Configuration file:

<VirtualHost *:8080>

    # ---- Configure VirtualHost Defaults ----

    ServerAdmin jsmith@whoi.edu 

    DocumentRoot /home/bitnami/public_html/http

    <Directory />
            Options FollowSymLinks
            AllowOverride None
    </Directory>

    <Directory /home/bitnami/public_html/http/>
            Options Indexes FollowSymLinks MultiViews
            AllowOverride None
            Order allow,deny
            Allow from all
    </Directory>

    # ---- Configure WSGI Listener(s) ----

    WSGIDaemonProcess flaskapp user=www-data group=www-data processes=1 threads=5
    WSGIScriptAlias /flasktest1 /home/bitnami/public_html/wsgi/flasktest1.wsgi 

    <Directory /home/bitnami/public_html/http/flasktest1>
            WSGIProcessGroup flaskapp
            WSGIApplicationGroup %{GLOBAL}
            Order deny,allow
            Allow from all
    </Directory>

    # ---- Configure Logging ----

ErrorLog /home/bitnami/public_html/logs/error.log
LogLevel warn
CustomLog /home/bitnami/public_html/logs/access.log combined

Here is the modified flask code

#!/usr/bin/python
from flask import Flask

import nltk
app = Flask(__name__)
@app.route('/')
def home():
    return """<html>
    <h2>Hello from Test Application 1</h2>
    </html>"""

@app.route('/<foo>')
def foo(foo):
    return """<html>
    <h2>Test Application 1</2>
    <h3>/%s</h3>
    </html>""" % foo

if __name__ == '__main__':
    "Are we in the __main__ scope? Start test server."
    app.run(host='0.0.0.0',port=5000,debug=True)

Can you post the relevant portion of HTTPd's error.log? – jd. Dec 15 '12 at 20:27 — jd., Dec 15 '12 at 20:27

score 6 · Accepted Answer · answered Dec 15 '12 at 23:27

Where you have:

<Directory /home/bitnami/public_html/http/flasktest1>
        WSGIProcessGroup flaskapp
        WSGIApplicationGroup %{GLOBAL}
        Order deny,allow
        Allow from all
</Directory>

it should be:

<Directory /home/bitnami/public_html/http>
        WSGIProcessGroup flaskapp
        WSGIApplicationGroup %{GLOBAL}
        Order deny,allow
        Allow from all
</Directory>

as you are neither running your app in daemon mode or in the main interpreter because of the directives being in the wrong context.

That Directory directive then conflicts with one for same directory above so merge them.

If using mod_wsgi 3.0 or later count instead perhaps drop that second Directory block and use:

WSGIDaemonProcess flaskapp threads=5
WSGIScriptAlias /flasktest1 /home/bitnami/public_html/wsgi/flasktest1.wsgi process-group=flaskapp application-group=%{GLOBAL}

Note that processes=1 has been dropped as that is the default and setting it implies other things you likely don't want. You also don't need to set user/group as it will automatically run as the Apache user anyway.

thanks for your help! I changed the virtual configuration file as you described and it worked: I removed the second element and removed /flasktest1 from the third. Btw, it was not nltk but numpy and pyyaml that caused the freezing — user1906763, Dec 18 '12 at 03:11

Flask WSGI application hangs when import nltk

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