Is there a way to log python print statements in gunicorn?

Question

With my Procfile like this:

web: gunicorn app:app \
    --bind "$HOST:$PORT" \
    --debug --error-logfile "-" \
    --enable-stdio-inheritance \
    --reload \
    --log-level "debug"

is it in any way possible to get python print statements to be logged to stdout / bash? I am using the bottle framework here as well, if that affects anything.

The debug flag doesn't apply to gunicorn. It actually fails if you try to run it: `gunicorn: error: unrecognized arguments: --debug` — Akronix, May 25 '18 at 11:11

score 34 · Answer 1 · answered Nov 23 '18 at 04:11

34

In python 3, adding flush=True in each print statement works for my flask/gunicorn app.

E.g.

gunicorn --bind 0.0.0.0:8080 server --log-level debug

No particular flags are required.

See if this helps.

answered Nov 23 '18 at 04:11

suvtfopw

648
8
15

1

It doesn't seem convenient to change the app code to work around this. – kontur Sep 25 '20 at 06:41

score 32 · Accepted Answer · answered Dec 29 '14 at 12:11

32

It turns out the print statements were actually getting through, but with delay.

The gunicorn docs for --enable-stdio-inheritance note to set the PYTHONUNBUFFERED, which I thought I had, but it seems with wrong syntax.

I solved it using a .env file with my foreman setup to set the variable like this:

PYTHONUNBUFFERED=TRUE

answered Dec 29 '14 at 12:11

kontur

4,027
1
33
58

Even though it is official way to do it - it does not work for unknown reason (python 2.7) – FelikZ Nov 04 '16 at 11:55

Satys · Answer 3 · 2019-08-09T05:44:40.880

Please try below command:

gunicorn --workers 3 --bind 127.0.0.1:5000 --error-logfile /var/log/gunicorn/error.log --access-logfile /var/log/gunicorn/access.log --capture-output --log-level debug

It did work for me.

Please specify log-level to debug(default info)http://docs.gunicorn.org/en/stable/settings.html#loglevel,

Also, specify capture-output flag (default false)http://docs.gunicorn.org/en/stable/settings.html#capture-output.

You should be able to watch logs in error log file.

score 6 · Answer 4 · edited Jun 20 '20 at 09:12

I use Python3 along with Flask.

I use print('log info') directly instead of print('log info', flush=True).

I only set capture_output to True and set a errorlog file and it works.

Note that:

capture_output

--capture-output
False
Redirect stdout/stderr to specified file in errorlog

I think it's that you need to specifiy a errorlog file to get the standard output.

Here's my config file gunicorn.config.py setting

accesslog = 'gunicorn.log'
errorlog = 'gunicorn.error.log'
capture_output = True

Then run with gunicorn app_py:myapp -c gunicorn.config.py

The equivaluent command line would be

gunicorn app_py:myapp --error-logfile gunicorn.error.log --access-logfile gunicorn.log --capture-output

Is there a way to log python print statements in gunicorn?

4 Answers4

capture_output

Linked