Configuring Python cx_Oracle and mod_wsgi on Oracle Linux

The Web Server Gateway Interface (WSGI) is a standardized interface between web servers and Python web frameworks or applications. Many frameworks including Django support WSGI.

This post is a brief how-to about configuring Apache's mod_wsgi with Python's cx_Oracle driver for Oracle Database. The steps are for Oracle Linux.

1. Download Instant Client Basic & SDK ZIP files from OTN. For cx_Oracle, use the ZIPs, not the RPMs.

2. As root, unzip the files to the same directory, e.g. /opt/oracle/instantclient_12_1:

   mkdir /opt/oracle
   cd /opt/oracle
   unzip /tmp/instantclient-basic-linux.x64-12.1.0.2.0.zip
   unzip /tmp/instantclient-sdk-linux.x64-12.1.0.2.0.zip

3. Configure Instant Client:

   cd /opt/oracle/instantclient_12_1
   ln -s libclntsh.so.12.1 libclntsh.so

4. Install the pip package management tool for Python by following pip.readthedocs.org/en/latest/installing.html and downloading get-pip.py. Then run:

   python get-pip.py

5. Install cx_Oracle:

   export LD_RUN_PATH=/opt/oracle/instantclient_12_1
   export ORACLE_HOME=/opt/oracle/instantclient_12_1
   pip install cx_Oracle

   The key here is the use of LD_RUN_PATH. This obviates the need to later set LD_LIBRARY_PATH or configureldconfig for cx_Oracle to find the Instant Client libraries. On Oracle Linux 7, which has Apache 2.4, settingLD_LIBRARY_PATH isn't practical since suEXEC is used. Configuring ldconfig is commonly used but has a potential problem that if multiple Oracle products exist, with possibly differing versions of Oracle libraries on the same machine, then there might be library clashes.

   The cx_Oracle installer overloads the meaning ofORACLE_HOME. This variable is not normally used for Instant Client installations.

   Neither ORACLE_HOME or LD_RUN_PATH needs to be set at runtime.

6. Install mod_wsgi:

     yum install mod_wsgi

7. Add this line to /etc/httpd/conf/httpd.conf:

      WSGIScriptAlias /wsgi_test /var/www/html/wsgi_test.py

8. On Oracle Linux 7, start the web server with:

     systemctl start httpd.service

   On Oracle Linux 6 use:

     service httpd start

9. Create a test file /var/www/html/wsgi_test.py that connects to your database:

       #-*- coding: utf-8 -*-
   
       def query():
   	import cx_Oracle
   	db = cx_Oracle.connect("hr", "welcome", "localhost/orcl")
   	cursor = db.cursor()
   	cursor.execute("select city from locations where location_id = 2200")
   	return cursor.fetchone()[0]
   
       def wsgi_test(environ, start_response):
   	output = query()
   
   	status = '200 OK'
   	headers = [('Content-type', 'text/plain'),
   		   ('Content-Length', str(len(output)))]
   	start_response(status, headers)
   	yield output
   
       application = wsgi_test
   

10. Load http://localhost/wsgi_test in a browser. The city of the queried location id will be displayed.

That's it. Let me know how it works for you.

Information on cx_Oracle can be found here.

Information on Oracle Linux can be found here.

Information on Oracle Database can be found here.