Logging stdout to gunicorn access log?

Question

When I wrap my Flask application in gunicorn writing to stdout no longer seems to go anywhere (simple print statements don\'t appear). Is there someway to either ca

Answer 1

Two solutions to this problem. They are probably longer than others, but ultimately they tap into how logging is done under the hood in Python.

1. set logging configuration in the Flask app

The official Flask documentation on logging works for gunicorn. https://flask.palletsprojects.com/en/1.1.x/logging/#basic-configuration

• some example code to try out:

from logging.config import dictConfig

from flask import Flask

dictConfig(
    {
        "version": 1,
        "disable_existing_loggers": False,
        "formatters": {
            "default": {
                "format": "[%(asctime)s] [%(process)d] [%(levelname)s] in %(module)s: %(message)s",
                "datefmt": "%Y-%m-%d %H:%M:%S %z"
            }
        },
        "handlers": {
            "wsgi": {
                "class": "logging.StreamHandler",
                "stream": "ext://flask.logging.wsgi_errors_stream",
                "formatter": "default",
            }
        },
        "root": {"level": "DEBUG", "handlers": ["wsgi"]},
    }
)
app = Flask(__name__)

@app.route("/")
def hello():
    app.logger.debug("this is a DEBUG message")
    app.logger.info("this is an INFO message")
    app.logger.warning("this is a WARNING message")
    app.logger.error("this is an ERROR message")
    app.logger.critical("this is a CRITICAL message")
    return "hello world"

• run with gunicorn

gunicorn -w 2 -b 127.0.0.1:5000 --access-logfile - app:app

• request it using curl

curl http://127.0.0.1:5000

• this would generate the following logs

[2020-09-04 11:24:43 +0200] [2724300] [INFO] Starting gunicorn 20.0.4
[2020-09-04 11:24:43 +0200] [2724300] [INFO] Listening at: http://127.0.0.1:5000 (2724300)
[2020-09-04 11:24:43 +0200] [2724300] [INFO] Using worker: sync
[2020-09-04 11:24:43 +0200] [2724311] [INFO] Booting worker with pid: 2724311
[2020-09-04 11:24:43 +0200] [2724322] [INFO] Booting worker with pid: 2724322
[2020-09-04 11:24:45 +0200] [2724322] [DEBUG] in flog: this is a DEBUG message
[2020-09-04 11:24:45 +0200] [2724322] [INFO] in flog: this is an INFO message
[2020-09-04 11:24:45 +0200] [2724322] [WARNING] in flog: this is a WARNING message
[2020-09-04 11:24:45 +0200] [2724322] [ERROR] in flog: this is an ERROR message
[2020-09-04 11:24:45 +0200] [2724322] [CRITICAL] in flog: this is a CRITICAL message
127.0.0.1 - - [04/Sep/2020:11:24:45 +0200] "GET / HTTP/1.1" 200 11 "-" "curl/7.68.0"

2. set logging configuration in Gunicorn

• same application code as above but without the dictConfig({...}) section

• create a logging.ini file

[loggers]
keys=root

[handlers]
keys=consoleHandler

[formatters]
keys=simpleFormatter

[logger_root]
level=DEBUG
handlers=consoleHandler

[handler_consoleHandler]
class=StreamHandler
level=DEBUG
formatter=simpleFormatter
args=(sys.stdout,)

[formatter_simpleFormatter]
format=[%(asctime)s] [%(process)d] [%(levelname)s] - %(module)s - %(message)s
datefmt=%Y-%m-%d %H:%M:%S %z

• run gunicorn with --log-config logging.ini option, i.e gunicorn -w 2 -b 127.0.0.1:5000 --access-logfile - --log-config logging.ini app:app

Answer 2

You can redirect standard output to a errorlog file, which is enough for me.

Note that:

capture_output

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

---

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

Answer 3

Use the logging: set the stream to stdout

import logging

app.logger.addHandler(logging.StreamHandler(sys.stdout))
app.logger.setLevel(logging.DEBUG)

app.logger.debug("Hello World")

Answer 4

The solution from John mee works, but it duplicates log entries in the stdout from gunicorn.

I used this:

import logging
from flask import Flask

app = Flask(__name__)

if __name__ != '__main__':
    gunicorn_logger = logging.getLogger('gunicorn.error')
    app.logger.handlers = gunicorn_logger.handlers
    app.logger.setLevel(gunicorn_logger.level)

and got I this from: https://medium.com/@trstringer/logging-flask-and-gunicorn-the-manageable-way-2e6f0b8beb2f