Develop Reference

Flask website -- 500 Internal Server Error

I cannot for the life of me figure of why this flask application I'm trying to launch is not working. I am running it on a $5 Digital Ocean droplet. Here's (hopefully) everything you need to know about it:
Directory layout (contained within /var/www/):
FlaskApp
FlaskApp
__init__.py
static
templates
venv
flaskapp.wsgi
__init__.py:
from flask import Flask
app = Flask(__name__)
#app.route("/")
def hello():
return "yay it worked"
if __name__ == "__main__":
app.run()
flaskapp.wsgi:
#!/usr/bin/python
import sys
import logging
logging.basicConfig(stream=sys.stderr)
sys.path.insert(0,"/var/www/FlaskApp/")
from FlaskApp import app as application
application.secret_key = 'Add your secret key'
FlaskApp.conf (contained in /etc/apache2/sites-availble):
<VirtualHost *:80>
ServerName the.ip.blah.blah
ServerAdmin admin#mywebsite.com
WSGIScriptAlias / /var/www/FlaskApp/flaskapp.wsgi
<Directory /var/www/FlaskApp/FlaskApp/>
Order allow,deny
Allow from all
</Directory>
Alias /static /var/www/FlaskApp/FlaskApp/static
<Directory /var/www/FlaskApp/FlaskApp/static/>
Order allow,deny
Allow from all
</Directory>
ErrorLog ${APACHE_LOG_DIR}/error.log
LogLevel warn
CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>
venv was created from calling virtualenv venv within /var/www/FlaskApp/FlaskApp/. I installed flask in venv using pip install flask after entering venv using source venv/bin/activate.
Wsgi has been enabled (a2enmod wsgi). FlaskApp.conf was enabled (a2ensite FlaskApp). And, finally, I restarted apache many times, but to no success (service apache2 restart).
I was following this guide on how to set up a flask application.
Here is a screenshot of what my error looks like:
Any help on getting this to work would be greatly appreciated.
Thanks in advance.
EDIT: I found the problem: ImportError: No module named flask. This is a little strange since I did do pip install flask within the virtualenv. When I just open a python console session in the virtualenv and try import flask I get no error, so not sure what's going on.
Also, how is this application even using venv? I don't see it getting accessed anywhere so how is it even using it? Perhaps this is why i'm getting the ImportError, because I only have flask installed on the virtualenv but it's not being used?

The problem is essentially that you are installing Flask, and possibly other required libraries, in a virtual environment but the python (wsgi interface) is running with the system python which does not have these extra libraries installed.
I have very little recent experience running Python on Apache (I come from an era of mod_python and cgi), but apparently one way to handle this is to use the site package to add the site-packages from your venv to the Python that is executed. This would go in your .wsgi file.
import site
site.addsitedir('/path/to/your/venv/lib/pythonX.X/site-packages')

I think the best way to solve your problem is to add tell your wsgi file about your virtual environment and activate it:
put the following code in your your flaskapp.wsgi
activate_this = '/path/to/env/bin/activate_this.py'
execfile(activate_this, dict(__file__=activate_this))
and restart apache.
hope it will help!
find more here

Why apache throws Target WSGI script not found or unable to stat on Flask app?

I want to setup my flask app for apache on my ubuntu server using wsgi. But after my setup, I get the following browser error:
Not Found
The requested URL / was not found on this server.
The apache error log throws:
Target WSGI script not found or unable to stat:
/var/www/html/appname/appname.wsgi
My wsgi file looks like this:
#!/usr/bin/python
import sys
import logging
logging.basicConfig(stream=sys.stderr)
sys.path.insert(0,"/var/www/html/appname/")
from IdeaHound import app as application
application.secret_key = 'here_the_key'
and my apache config file looks like this:
<VirtualHost *:80>
ServerName server_ip_here
WSGIScriptAlias / /var/www/html/appname/appname.wsgi
<Directory /var/www/html/appname/>
Order allow,deny
Allow from all
</Directory>
ErrorLog ${APACHE_LOG_DIR}/error.log
LogLevel info
CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>
The appname folder has the following structure:
appname
--application.py
--appname.wsgi
--LICENSE
--README.md
--requirements.txt
--db_manage.py
--appname
----frontend
----__inity__.py
----__init__.pyc
----models
----__pycache__
----socket_interface
--AppName
----__init__.py
----static
----templates
--instance
----config.py
What am I missing here to make the webserver run correctly with Flask?

Please read the following link of Digital Ocean. Do as describe in it. And your app will be up and running in just 5 mins.
https://www.digitalocean.com/community/tutorials/how-to-deploy-a-flask-application-on-an-ubuntu-vps
Also do check the apache error logs for more information if it still throws an error.
/var/log/apache2/error.log

Apache set-up with Flask and wsgi

I have a small web application that I have built using Flask and python. With the internal server that I used for developing everything runs fine. However now I want to use apache to start using it. But it doesn`t work. Keep in mind that I have never worked with apache or web based stuff before.
I used this guide as my starting point:
http://flask.pocoo.org/docs/deploying/mod_wsgi/
right now I have my application which is in the file called "/rg/server.py" and looks like this:
app=Flask(__name__)
# all app routes...
if __name__ == '__main__':
app.run(
debug=True,
host="127.0.0.1",
port=80
)
than I have a wsgi file as "/rg/wsgi/minerva.wsgi"
import sys
sys.path.insert(0, /rg)
from server import app as minerva
and finally I have an apache config file in "etc/apach2/sites-available/minerva.com":
<VirtualHost *>
ServerName minerva.test
WSGIDaemonProcess minerva threads=10
WSGIScriptAlias / /rg/wsgi/minerva.wsgi
<Directory /rg>
WSGIProcessGroup minerva
WSGIApplicationGroup %{GLOBAL}
Order deny,allow
Allow from all
</Directory>
</VirtualHost>
Then I updated apache with a2ensite minerva.com which succeded. Then I releaded Apache and no errors. However I cannot acces minerva.test in any way...
If I type in apache2ctl -S it does list minerva.test
I have no idea what is going wrong...
system information:
OS: debian 64bit
python 2.7

The WSGI application entry point must be called 'application' for mod_wsgi. You have:
from server import app as minerva
It should be:
from server import app as application
You aren't even getting that far though, else the line:
sys.path.insert(0, /rg)
would give a syntax error.
Going back further, instead of:
<VirtualHost *>
you should have:
<VirtualHost *:80>
and finally, if 'minerva.test' isn't actually a resolvable host, you will not get anywhere.
So fill out your question with the actual URL you are using in the browser and also indicate whether 'minerva.test' is even listed in local hosts file.

The first thing I would check would be to make sure mod_wsgi is installed and loaded by apache. If that's fine, your setup looks pretty similar to mine with a few minor differences:
I had to add WSGISocketPrefix /var/run/wsgi above my VirtualHost definitoin. See here.
I included user and group values on the WSGIDaemonProcess line.

mod_wsgi configuration with flask

I have a problem with mod_wsgi and flask Im not sure what it is after almost 48 hours of trying I've finally given up and need some help. Everything seems fine and working properly I know this because my www.example.com domain routes to example.com/login if the user is not logged in.
When I access example.com the routing does happen and I can see the url change to example.com/login
Here is my configuration:
killerapp.wsgi:
from main import app as application
and the apache virtual host:
NameVirtualHost *:8080
<VirtualHost *:8080>
ServerName example.com
WSGIDaemonProcess killerapp user=apache group=apache threads=5
WSGIScriptAlias / /var/www/wsgi/killerapp.wsgi
<Directory /var/www/wsgi>
WSGIProcessGroup killerapp
WSGIApplicationGroup %{GLOBAL}
Order deny,allow
Allow from all
</Directory>
</VirtualHost>
I was getting the following error all along
ImportError: No module named app
when I did
chmod 755 app
on the app folder I got the following in the log file indicating no errors:
[Wed Nov 06 17:25:29 2013] [info] [client xx.xx.x.xxx] mod_wsgi (pid=3823, process='killerapp', application=''): Loading WSGI script '/var/www/wsgi/killerapp.wsgi
But i still get the following error when I access the page:
The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there is an error in the application.
I suspect its a ownership/security issue but that's just my guess I wouldn't know at this point. If its of any help Im running python 2.6.6 on Centos 6.4 and mod_wsgi 3.2.3
Any help would really be appreciated.
Thank you

With many thanks to Mark Hildreth for showing me the 'way' I managed to finally see what the problem was. It was a permission issue
In my python app I turned on debugging after initializing the flask app like so:
app = Flask(__name__)
app.debug = True
This allowed Flask to display the error messages in the apache error log. In my case the problem was Jinja was unable to access the templates directory because the apache user was not set as owner of that directory so the following fixed it:
chown apache:apache templates
Once again credit and thanks goes to Mark Hildreth for showing me the light!

django, apache, mod_wsgi and python py-scrypt not working together

I am running a ec2 instance to host some Django websites. The websites are being served by Apache with the use of mod_wsgi
Since a few days I am trying to deploy a new webplatform we are developing but I am running into a problem that seems impossible for me to solve. For security reasons we use scrypt 0.4 to secure the users personal information like passwords.
On the development server everything works like a charm but when we deploy to our live server we get a 500 Internal Server error. The apache log gives me the following message
Premature end of script headers: socialmarketingplatform.wsgi, referer:
When I uncomment the line where the scrypt module is used everything works fine. Also when I run the server delivered with Django with scrypt enabled everything works on the live server. So it is a combination of mod_wsgi, django and scrypt that generates the error.
I am using the following wsgi file:
import os
import sys
path = '/var/www/vhosts/[sub_domain]'
if path not in sys.path:
sys.path.append(path)
sys.path.append(path + '/socialmarketingplatform')
os.environ['DJANGO_SETTINGS_MODULE'] = 'socialmarketingplatform.settings'
import django.core.handlers.wsgi
application = django.core.handlers.wsgi.WSGIHandler()
And the following virtualhost config:
<VirtualHost *:80>
#Basic setup
ServerAdmin [removed email]
ServerName luxdevelopment.net
ServerAlias [sub domain]
DocumentRoot /var/www/vhosts/[sub domain]/socialmarketingplatform/
Alias /media/admin /usr/lib/python2.6/site-packages/Django-1.3-py2.6.egg/django/contrib/admin/media
Alias /media /var/www/vhosts/[sub domain]/socialmarketingplatform/media
<Location media="">
SetHandler None
</Location>
LogLevel warn
ErrorLog /var/log/httpd/smp_error.log
CustomLog /var/log/httpd/smp_access.log combined
WSGIDaemonProcess luxdevelopment.net user=apache group=apache threads=25
WSGIProcessGroup luxdevelopment.net
WSGIScriptAlias / /var/www/cgi-bin/socialmarketingplatform.wsgi
</VirtualHost>
I hope someone can help me with this problem. If there are any further question let me know.

See:
http://code.google.com/p/modwsgi/wiki/FrequentlyAskedQuestions#Apache_Process_Crashes
The message 'premature end of script headers' is usually indicative of your code crashing the daemon process. You can verify this by looking for segmentation fault or similar message in main Apache error log file. If you enable 'LogLevel info' in main Apache config and VirtualHost then mod_wsgi will log more about daemon process restarts.
A quick remedy if running only application in that daemon process group is to add:
WSGIApplicationGroup %{GLOBAL}
This will work around crashes caused by broken third party extension modules for Python which aren't written properly to work in sub interpreters.
Other than that, can be shared library version mismatches as described in the FAQ.