uWSGI works as process but not as daemon - flask

Question

For my current flask deployment, I had to set up a uwsgi server.
This is how I have created the uwsgi daemon:
sudo vim /etc/init/uwsgi.conf
# file: /etc/init/uwsgi.conf
description "uWSGI server"
start on runlevel [2345]
stop on runlevel [!2345]
respawn
exec /myproject/myproject-env/bin/uwsgi --uid www-data --gid www-data --home /myproject/myproject-env/site/F11/Engineering/ --socket /tmp/uwsgi.sock --chmod-socket --module F11 --callable app --pythonpath /myproject/myproject-env/site/F11/Engineering/ -H /myproject/myproject-env
However after running this successfully: sudo start uwsgi
uwsgi start/running, process 1286
And trying to access the application via browser:
I get a 502 Bad Gateway
and an error entry in nginx error.log:
2013/06/13 23:47:28 [error] 743#0: *296 upstream prematurely closed
connection while reading response header from upstream, client:
xx.161.xx.228, server: myproject.com, request: "GET /show_records/2013/6 HTTP/1.1", upstream:
"uwsgi://unix:///tmp/uwsgi.sock:", host: "myproject.com"
But the sock file has the permission it needs:
srw-rw-rw- 1 www-data www-data 0 Jun 13 23:46 /tmp/uwsgi.sock
If I run the exec command from above in the command line as a process, it works perfectly fine. Why is the daemon not working correctly please?
btw Nginx is running as
vim /etc/nginx/nginx.conf
user www-data;
and vim /etc/nginx/sites-available/default
location / {
uwsgi_pass unix:///tmp/uwsgi.sock;
include uwsgi_params;
}
and it is started as sudo service nginx start
I am running this on Ubuntu 12.04 LTS.
I hope I have provided all the necessary data, hope someone can guide me into the right direction. Thanks.

Answer 1

Finally I have solved this problem after working nearly 2 days on it. I hope this solution will help other flask/uwsgi users that are experiencing a similar problem.
I had two major issues that caused this.
1) The best way to find the problems with a daemon is obviously a log file and a cleaner structure.
sudo vim /etc/init/uwsgi.conf
Change the daemon script to the following:
# file: /etc/init/uwsgi.conf
description "uWSGI server"
start on runlevel [2345]
stop on runlevel [!2345]
respawn
exec /home/ubuntu/uwsgi-1.9.12/uwsgi -c /myproject/uwsgi.ini
vim /myproject/uwsgi.ini
[uwsgi]
socket = /tmp/uwsgi.sock
master = true
enable-threads = true
processes = 5
chdir= /myproject/F11/Engineering
module=F11:app
virtualenv = /myproject/myproject-env/
uid = www-data
gid = www-data
logto = /myproject/error.log
This is much cleaner way of setting up the daemon. Also notice the last line how to setup the log file. Initially I had set the log file to /var/log/uwsgi/error.log. After a lot of sweat and tears I realized the daemon is running as www-data and hence can not access the /var/log/uwsgi/error.log since the error.log was owned by root:root. This made the uwsgi fail silently.
I found it much more efficient to just point the log file to my own /myproject, where the daemon has guaranteed access as www-data. And also don't forget to make the whole project accessible to www-data or the daemon will fail with an Internal Server error message. -->
sudo chown www-data:www-data -R /myproject/
Restart uwsgi daemon:
sudo service uwsgi restart
2) Now you have three log files to lookout for:
tail -f /var/log/upstart/uwsgi.log --> Shows problems with your daemon upon start
tail -f /var/log/nginx/error.log --> Shows permission problems when wsgi access is refused, often because /tmp/uwsgi.sock file is owned by root instead of www-data. In that case simply delete the sock file sudo rm /tmp/uwsgi.sock
tail -f /myproject/error.log --> Shows errors thrown by uwsgi in your application
This combination of log files helped me to figure out that I also had a bad import with Flask-Babel in my Flask application. Bad in that sense, that the way I utilized the library was falling back to the system's locale to determine the datetime format.
File "/myproject/F11/Engineering/f11_app/templates/show_records.html", line 25, in block "body"
<td>{{ record.record_date|format_date }}</td>
File "./f11_app/filters.py", line 7, in format_date
day = babel_dates.format_date(value, "EE")
File "/myproject/myproject-env/local/lib/python2.7/site-packages/babel/dates.py", line 459, in format_date
return pattern.apply(date, locale)
File "/myproject/myproject-env/local/lib/python2.7/site-packages/babel/dates.py", line 702, in apply
return self % DateTimeFormat(datetime, locale)
File "/myproject/myproject-env/local/lib/python2.7/site-packages/babel/dates.py", line 699, in __mod__
return self.format % other
File "/myproject/myproject-env/local/lib/python2.7/site-packages/babel/dates.py", line 734, in __getitem__
return self.format_weekday(char, num)
File "/myproject/myproject-env/local/lib/python2.7/site-packages/babel/dates.py", line 821, in format_weekday
return get_day_names(width, context, self.locale)[weekday]
File "/myproject/myproject-env/local/lib/python2.7/site-packages/babel/dates.py", line 69, in get_day_names
return Locale.parse(locale).days[context][width]
AttributeError: 'NoneType' object has no attribute 'days'
This is the way I was using the Flask filter:
import babel.dates as babel_dates
#app.template_filter('format_date')
def format_date(value):
day = babel_dates.format_date(value, "EE")
return '{0} {1}'.format(day.upper(), affix(value.day))
The strangest part is that this code is working perfectly fine within the dev environment (!). It works even fine when running the uwsgi as a root process from the command line. But it fails when ran by the www-data daemon. This must have something to do with how the locale is set, which Flask-Babel is trying to fall back to.
When I changed the import like this, it all worked finally with the daemon:
from flask.ext.babel import format_date
#app.template_filter('format_date1')
def format_date1(value):
day = format_date(value, "EE")
return '{0} {1}'.format(day.upper(), affix(value.day))
Hence be careful when using Eclipse/Aptana Studio that is trying to pick the right namespace for your classes in code. It can really turn ugly.
It is now working perfectly fine as a uwsgi daemon on an Amazon Ec2 (Ubuntu 12.04) since 2 days. I hope this experience helps fellow python developers.

Answer 2

I gave up, there was no uwsgi.log generated, and nginx just kept complaining about :
2014/03/06 01:06:28 [error] 23175#0: *22 upstream prematurely closed connection while reading response header from upstream, client: client.IP, server: my.server.IP, request: "GET / HTTP/1.1", upstream: "uwsgi://unix:/var/web/the_gelatospot/uwsgi.sock:", host: "host.ip"
for every single request. This only happened if running uwsgi as a service, as a process it started fine under any user. So this would work from command line (page responds):
$exec /var/web/the_gelatospot/mez_server.sh
This didn't (/etc/init/site_service.conf):
description "mez sites virtualenv and uwsgi_django" start on runlevel
[2345] stop on runlevel [06] respawn respawn limit 10 5 exec
/var/web/the_gelatospot/mez_server.sh
The process would start but on each request nginx would complain about the closed connection. Strangely I have this same config working just fine for 2 other apps using the same nginx version and same uwsgi version as well as both apps are mezzanine CMS apps. I tried everything I could think of and what was suggested. In the end I switched to gunicorn which works fine:
#!/bin/bash
NAME="the_gelatospot" # Name of the application
DJANGODIR=/var/web/the_gelatospot # Django project directory
SOCKFILE=/var/web/the_gelatospot/gunicorn.sock # we will communicte using this unix socket
USER=ec2-user
GROUP=ec2-user # the user to run as, the group to run as
NUM_WORKERS=3 # how many worker processes should Gunicorn spawn
DJANGO_SETTINGS_MODULE=settings
#DJANGO_SETTINGS_MODULE=the_gelatospot.settings # which settings file should Django use
#DJANGO_WSGI_MODULE=the_gelatospot.wsgi # WSGI module name
DJANGO_WSGI_MODULE=wsgi
echo "Starting $NAME as `the_gelatospot`"
# Activate the virtual environment
cd $DJANGODIR
source ../mez_env/bin/activate
export DJANGO_SETTINGS_MODULE=$DJANGO_SETTINGS_MODULE
export PYTHONPATH=$DJANGODIR:$PYTHONPATH
# Create the run directory if it doesn't exist
RUNDIR=$(dirname $SOCKFILE)
test -d $RUNDIR || mkdir -p $RUNDIR
cd ..
# Start your Django GUnicorn
# Programs meant to be run under supervisor should not daemonize themselves (do not use --daemon)
exec gunicorn -k eventlet ${DJANGO_WSGI_MODULE}:application \
--name $NAME \
--workers $NUM_WORKERS \
--log-level=debug \
--bind=unix:$SOCKFILE
And here is the one that wouldn't work as a service (nginx complaining of prematurely closed connection and no app log data coming through).
#!/bin/bash
DJANGODIR=/var/web/the_gelatospot/ # Django project directory
cd $DJANGODIR
source ../mez_env/bin/activate
uwsgi --ini uwsgi.ini
And the uwsgi.ini:
[uwsgi]
uid = 222
gid = 500
socket = /var/web/the_gelatospot/uwsgi.sock
virtualenv = /var/web/mez_env
chdir = /var/web/the_gelatospot/
wsgi-file = /var/web/the_gelatospot/wsgi.py
pythonpath = ..
env = DJANGO_SETTINGS_MODULE=the_gelatospot.settings
die-on-term = true
master = true
chmod-socket = 666
;experiment using uwsgitop
worker = 1
;gevent = 100
processes = 1
daemonize = /var/log/nginx/uwsgi.log
logto = /var/log/nginx/uwsgi.logi
log-maxsize = 10000000
enable-threads = true
I went from gunicorn to uWSGI last year and I had no issues with it till now, it also seemed a bit faster than gunicorn. Right now I'm thinking of sticking to gunicorn. Its getting better, puts up much nicer numbers with eventlet installed, and it is easier to configure.
Hope this workaround helps. I would still like to know the issue with uWSGI and nginx but I'm stumped.
Update:
So using gunicorn allowed me to run the server as a service and while toying in mezzanine I ran into this error: FileSystemEncodingChanged
To fix this I found the solution here:
https://groups.google.com/forum/#!msg/mezzanine-users/bdln_Y99zQw/9HrhNSKFyZsJ
And I had to modify it a bit since I don't use supervisord, I only use upstart and a shell script. I added this to right before I execute gunicorn in my mez_server.sh file:
export LANG=en_US.UTF-8, LC_ALL=en_US.UTF-8, LC_LANG=en_US.UTF-8
exec gunicorn -k eventlet ${DJANGO_WSGI_MODULE}:application \
--name $NAME \
--workers $NUM_WORKERS \
--log-level=debug \
--bind=unix:$SOCKFILE
I also tried this fix using uWSGI like so ( a lot shorter since using uwsgi.ini ):
export LANG=en_US.UTF-8, LC_ALL=en_US.UTF-8, LC_LANG=en_US.UTF-8
exec uwsgi --ini uwsgi.ini
I am still sticking to gunicorn since it still worked with the problem and lead me in the right direction to resolve it. I was very disappointed that uWSGI provided no output in the log file even with these params, I only seen the server start process and that's it:
daemonize = /var/log/nginx/uwsgi.log
logto = /var/log/nginx/uwsgi.logi
While nginx kept throwing the disconnect error, uWSGI sat there like nothing is happening.

Answer 3

As a single line running with daemon true command is
gunicorn app.wsgi:application -b 127.0.0.1:8000 --daemon
bind your app with 127.0.0.1:8000 and --deamon force it to run as daemon
but define a gunicorn_config.cfg file and run with -c flag is good practice
for more:
https://gunicorn-docs.readthedocs.org/en/develop/configure.html