That worked perfectly, Graham. Thank you!
I read the documentation on WSGIApplicationGroup, and I'm afraid I didn't
completely understand it. Is there any downside to using %{GLOBAL}
routinely instead of the default?
I don't have a lot of applications running on this server. My "production"
application, which is the only one I care about, is defined thus:
WSGIApplicationGroup %{GLOBAL}
WSGIDaemonProcess md user=scott processes=1 threads=8
display-name=apache2-md home=/var/www/html/scott/prod
WSGIScriptAlias /scott/prod/md /var/www/html/scott/prod/md.wsgi
process-group=md
So, this is using daemon mode, right? It didn't work before I set
WSGIApplicationGroup
to %{GLOBAL}, but it does now. Is there any flaw with this combination of
settings?
Thanks again,
Scott
On Wed, Jul 26, 2017 at 5:15 PM, Graham Dumpleton <
[email protected]> wrote:
> The numpy package can fail when used in Python sub interpreters.
>
> Preferably use daemon mode, but more importantly delegate the WSGI
> application to run in the main interpreter context by setting
> WSGIApplicationGroup.
>
> http://modwsgi.readthedocs.io/en/develop/user-guides/
> application-issues.html#python-simplified-gil-state-api
>
> See if that changes anything.
>
> If not, next issue would be to make sure lang/locale is set to reasonable
> value.
>
> Graham
>
> On 27 Jul 2017, at 4:36 AM, Scott D Anderson <[email protected]>
> wrote:
>
> This might be the wrong venue for this question, but WSGI is part of the
> trouble, and Graham is always so helpful and responsive that it seems best
> to start here.
>
> I ran into a difficult-to-debug error in a Flask application, which I
> eventually boiled down to a very short example. I'll give the complete
> implementation with logs below, but let me start at the high level:
>
> The high-level description is pretty simple: there's a data structure
> that I had a "print" statement for. The print statement works perfectly in
> the development version, but when I run the code in a "production" WSGI
> environment, the print statement causes the server process to hang, with a
> "500 Internal Server Error" in the browser. So, somehow, printing is
> fundamentally different between development and WSGI, so I thought to start
> here.
>
> Here's the complete code for the application:
>
> from flask import Flask
>
> import pandas
> import numpy
>
> application = Flask(__name__)
>
> @application.route('/')
> def index():
> print('about to load JSON')
> df = pandas.read_json('/var/www/html/scott/prod/dfbad.json')
> print('JSON loaded')
> print('df is ',df)
> return '<!doctype html><html><body>df is '+str(df)+'</body></html>'
>
>
> if __name__ == '__main__':
> port = 5000
> application.run('0.0.0.0',port=port)
>
> In development mode, the (slightly edited) console output looks like this:
>
> about to load JSON
> JSON loaded
> ('df is ', basal_amt bolus_volume carbs date_time rec_num
> 0 0.375 NaN NaN 2016-04-03 18:31:00 18539
> 1 0.000 NaN NaN 2016-04-03 18:37:00 18540
> ...
> 7 1.100 NaN NaN 2016-04-03 20:31:00 18546
> 8 0.000 NaN NaN 2016-04-03 21:13:00 18547
> 9 1.100 NaN NaN 2016-04-03 21:16:00 18548)
> 127.0.0.1 - - [26/Jul/2017 10:47:05] "GET / HTTP/1.1" 200 -
>
> The GET response looks like this:
>
> GET http://localhost:5000/
> <!doctype html><html><body>df is basal_amt bolus_volume carbs
> date_time rec_num
> 0 0.375 NaN NaN 2016-04-03 18:31:00 18539
> 1 0.000 NaN NaN 2016-04-03 18:37:00 18540
> ...
> 7 1.100 NaN NaN 2016-04-03 20:31:00 18546
> 8 0.000 NaN NaN 2016-04-03 21:13:00 18547
> 9 1.100 NaN NaN 2016-04-03 21:16:00
> 18548</body></html>
>
> However, if I set up a WSGI production version (apache2, version
> 2.4.18-2ubuntu3.3) like this:
>
> WSGIScriptAlias /df_not_printable /var/www/html/scott/prod/df_
> not_printable.py
>
> Then the response to the GET request is the following:
>
> GET http://localhost/df_not_printable
> read timeout at /usr/share/perl5/Net/HTTP/Methods.pm line 273, <STDIN>
> line 2.
>
> The /var/log/apache2/error.log shows the following:
>
> [Wed Jul 26 10:48:09.164138 2017] [wsgi:info] [pid 2291] mod_wsgi
> (pid=2291): Create interpreter 'ip-132-148-72-77.ip.secureserver.net
> |/df_not_printable'.
> [Wed Jul 26 10:48:09.165605 2017] [wsgi:info] [pid 2291] [client
> 127.0.0.1:48072] mod_wsgi (pid=2291, process='', application='
> ip-132-148-72-77.ip.secureserver.net|/df_not_printable'): Loading WSGI
> script '/var/www/html/scott/prod/df_not_printable.py'.
> [Wed Jul 26 10:48:09.658077 2017] [wsgi:error] [pid 2291] about to load
> JSON
> [Wed Jul 26 10:48:09.701097 2017] [wsgi:error] [pid 2291] JSON loaded
>
> So, you can see that the first two 'print' statements worked fine and went
> to the log, but trying to print this pandas dataframe caused a
> catastrophe. There is nothing more in the logs; that's the last line.
> There's no stack backtrace, no exception, no hint about what could possibly
> have gone wrong. Maybe some kind of infinite loop?
>
> I know it's tempting just to blame pandas for the trouble, but I haven't a
> clue about what went wrong or how to debug this. Obviously, for now I'll
> just avoid printing any dataframes, but I worry about other unprintable
> objects out there.
>
> Thanks,
>
> Scott
> --
> Scott D. Anderson
> Computer Science Department
> Wellesley College
> [email protected]
> [email protected]
> pronouns: he, him, his
>
>
>
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--
Scott D. Anderson
Computer Science Department
Wellesley College
[email protected]
[email protected]
pronouns: he, him, his
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