Hosting a Python Flask App on AWS Ubuntu (EC2) using cx_Oracle and mod_wsgi

Question

I'm trying to host a simple Python Flask website that connects to an Oracle DB.

So far I've managed to install cx_Oracle (and the Oracle Client and SDK) on the Ubuntu host and host the Flask app successfully using Apache2 and mod_wsgi.

I followed this guide to install cx_Oracle: https://blogs.oracle.com/opal/entry/configuring_python_cx_oracle_and I followed this tutorial to host: http://blog.garethdwyer.co.za/2013/07/getting-simple-flask-app-running-on.html

The entire application functions perfectly when run locally from the instance. I've used x-forwarding and firefox to test this.

However, when I try to host publicly, running through wsgi, it can load the flask app, but fails when asked to access the Oracle database. I can't get error logs, since the Apache logs only show what I manually print out through Python. (If anyone has a fix for THAT, please tell).

I've spent far too much time trying to host - this should be much simpler than it is. Solutions?

My directory structure

->/var/www/SACK
    ->app.py
    ->app.wsgi
    ->satic/
    ->templates/
->/etc/apache2/sites-available
    ->sitename.com.config
->/opt/oracle/instant_client_12_1
    ->... Oracle client stuff. SDK included.

app.py

app = Flask(__name__)

...

def connectToDB():
    ip = '...'
    port = ...
    SID = '...'

    dsn_tns = cx_Oracle.makedsn(ip, port, SID)
    global connection 
    connection = cx_Oracle.connect('...', '...', dsn_tns)

    print "connection successful"
    global cursor 
    cursor = connection.cursor()


def closeConnection():
    cursor.close()
    connection.close()
    print "connection closed"

def main():
    connectToDB()
    app.run()
    closeConnection()

if __name__ == '__main__':
    main()

From those guides, here is how my app is set up for wsgi:

app.wsgi

import sys
sys.path.insert(0, '/var/www/SACK')

from app import app as application

Site Config:

sitename.com.config

<VirtualHost *:80>
         WSGIDaemonProcess SACK
     WSGIScriptAlias / /var/www/SACK/app.wsgi

     <Directory /var/www/SACK>
            WSGIProcessGroup SACK
        WSGIApplicationGroup %{GLOBAL}
        Order deny,allow
        Allow from all
     </Directory>
LogLevel info
ErrorLog "/var/log/apache2/error.log"
CustomLog "/var/log/apache2/access.log" combine
</VirtualHost>

Answer 1

My wsgi is configured to only run the actual Flask app itself, aka, the code contained within app.run() , therefore the connectToDB() function never actually runs when wsgi creates the application.

Rather than fixing this in my wsgi config, I used flask's @app.before_request() and @app.teardown_request annotations to create and destroy the DB connection.

The changes in code:

@app.before_request()
def connectToDB():
    ....

@app.teardown_request()
def closeConnection(e):
    ....