Which logger to use in a Python Flask app with Connexion

Question

I'm using both Flask and Connexion for a Python based REST API, and it runs within a Docker container. Here is main.py:

import connexion
import logging
from app.log import handler

# initiate swagger/connexion
application = connexion.App(__name__, specification_dir='./')
application.add_api('swagger.yml')

# logging
application.app.logger.handlers.clear()
application.app.logger.addHandler(handler)
application.app.logger.setLevel(logging.DEBUG)
application.app.logger.debug('application starting...')

# if we're running in standalone mode, run the application
if __name__ == '__main__':
    application.run(host='0.0.0.0', port=5000, debug=True)

This works fine, and in my syslog server I can see:

2020-01-14 11:03:14,951 app main:DEBUG application starting...

However, I'm not sure how to log correctly from files outside of main.py. For example, I have a status.py which has a single route for GET /status and the code looks like:

import yaml
from flask import current_app
import logging

def read():

    # LOG TESTING
    current_app.logger.debug('Test using current_app')
    logging.getLogger(__name__).debug('Test using getLogger')
    print('Test using print')

    with open('./swagger.yml', 'r') as f:
        y = yaml.load(f)

    return {
        # .... some data here
    }

In my syslog server, I can see:

Test using print
./status.py:22: YAMLLoadWarning: calling yaml.load() without Loader=... is deprecated, as the default Loader is unsafe. Please read https://msg.pyyaml.org/load for full details.
  y = yaml.load(f)

I would like to use the same logging mechanism that main.py is using in all of my separate files, but I can only get it to work from main.py, and the only thing that works outside of main.py is the print function, however, as can be seen above, errors also seem to get picked up (albeit with no timestamp).

Answer 1

Please review the docs here. https://flask.palletsprojects.com/en/1.1.x/logging/ You are changing the logging after calling app.log or is it app.logger (I forget) so the application has already started. You need to override the default. The document covers it but here is a gist.

Before you instantiate the Flask App. do this

from logging.config import dictConfig

dictConfig({
    'version': 1,
    'formatters': {'default': {
        'format': '[%(asctime)s] %(levelname)s in %(module)s: %(message)s',
    }},
    'handlers': {'wsgi': {
        'class': 'logging.StreamHandler',
        'stream': 'ext://flask.logging.wsgi_errors_stream',
        'formatter': 'default'
    }},
    'root': {
        'level': 'INFO',
        'handlers': ['wsgi']
    }
})

app = Flask(__name__) # important!  logging stuff is set before this.

One thing to note is that error from web request get logged differently than the errors outside of web requests (for e.g. jobs, cli etc). The default behavior is to log to standard error which in your case is syslog