Flask Request within request fails on production WSGI environment - apache

Question

I am making a request within a request, in order to accommodate my service oriented design. Locally, this code works. However on production using ubuntu libapache2-mod-wsgi-py3, my nested request fails.
A key point is both services exist within the same <Virtualhost> on the server, so I suspect this is a threading issue.
The second request called within newitem() fails with ConnectionRefusedError(111, 'Connection refused') on my WSGI Ubuntu box even though the API endpoint functions as expected when I POST to it outside of this context (for example curl POST to the exact url).
Another important point is this request within reqest design works on my local when I have two separate flask apps running on different ports. I had this exact issue on my local until I ran the API server with --threaded flag.
My server is configured as follows:
app2.wsgi:
#!env/bin/python3
import sys, os
sys.path.append('/var/www/api_app')
from app import create_app
from flask.ext.script import Manager
from flask.ext.migrate import Migrate, MigrateCommand
application = create_app(os.getenv('FLASK_CONFIG') or 'default')
if __name__ == "__main__":
manager.run()
apache2/sites-available/default.conf:
<VirtualHost *:80>
DocumentRoot /var/www/html
# ------ WSGI config ------
WSGIDaemonProcess app1 user=www-data group=www-data threads=5
WSGIDaemonProcess app2 user=www-data group=www-data threads=5
WSGIScriptAlias /front_end /var/www/front_end/app2.wsgi
WSGIScriptAlias /api_app /var/www/api_app/app2.wsgi
WSGIScriptReloading On
<Directory /var/www/api_app>
WSGIProcessGroup app2
WSGIApplicationGroup %{GLOBAL}
Order deny,allow
Allow from all
</Directory>
<Directory /var/www/front_end>
WSGIProcessGroup app1
WSGIApplicationGroup %{GLOBAL}
Order deny,allow
Allow from all
</Directory>
</VirtualHost>
The following code works great on my local environment when I start the API service with the --threaded flag It fails on WSGI Apache2 on the requests.post() line.
#plant_material.route('/plant_material/new', methods=['GET', 'POST'])
def newitem():
form = PlantMaterialForm()
if form.validate_on_submit():
api_uri = current_app.config['API_SERVER_URI']
url = api_uri + "api/plant_material/new"
headers = {'Content-Type': 'application/json'}
print(request.form)
r = requests.post(url, data=json.dumps(request.form), headers=headers)
if r.status_code == 200:
return redirect(url_for('plant_material.index'))
elif r.status_code == 401:
flash('Whiteboard API Unauthorized')
elif r.status_code == 403:
flash('Whiteboard API Forbidden')
elif r.status_code == 500:
flash('Internal Server Error')
return render_template('plant_material/new.html', form=form)
How can I make a request within a request on my production server?

Answer 1

Apache and mod_wsgi take care of concurrency here; there is no reason for a well-formed request from one WSGI app to another on the same server to fail here.
Make sure that there is no firewall blocking requests to the server from localhost. Test the same URL from the command line with curl for example.
Triple-check your assumptions; use the live value of current_app.config['API_SERVER_URI'] when testing if your connections work, not what you assume it to be.
swap out HTTP methods; try running curl from a subprocess call, or use urllib2 to access the API