Logging with WSGI server and flask application

Question

I am using wsgi server to spawn the servers for my web application. I am having problem with information logging.

This is how I am running the app

from gevent import monkey; monkey.patch_all()
from logging.handlers import RotatingFileHandler
import logging
from app import app # this imports app

# create a file to store weblogs
log = open(ERROR_LOG_FILE, 'w'); log.seek(0); log.truncate();
log.write("Web Application Log\n"); log.close();

log_handler = RotatingFileHandler(ERROR_LOG_FILE, maxBytes =1000000, backupCount=1)

formatter = logging.Formatter(
    "[%(asctime)s] {%(pathname)s:%(lineno)d} %(levelname)s - %(message)s"
    )
log_handler.setFormatter(formatter)
app.logger.setLevel(logging.DEBUG)
app.logger.addHandler(log_handler)

# run the application
server=  wsgi.WSGIServer(('0.0.0.0', 8080), app)
server.serve_forever()

However, on running the application it is not logging anything. I guess it must be because of WSGI server because app.logger works in the absence of WSGI. How can I log information when using WSGI?

Answer 1

According to the gevent uwsgi documentation you need to pass your log handler object to the WSGIServer object at creation:

log – If given, an object with a write method to which request (access) logs will be written. If not given, defaults to sys.stderr. You may pass None to disable request logging. You may use a wrapper, around e.g., logging, to support objects that don’t implement a write method. (If you pass a Logger instance, or in general something that provides a log method but not a write method, such a wrapper will automatically be created and it will be logged to at the INFO level.)

error_log – If given, a file-like object with write, writelines and flush methods to which error logs will be written. If not given, defaults to sys.stderr. You may pass None to disable error logging (not recommended). You may use a wrapper, around e.g., logging, to support objects that don’t implement the proper methods. This parameter will become the value for wsgi.errors in the WSGI environment (if not already set). (As with log, wrappers for Logger instances and the like will be created automatically and logged to at the ERROR level.)

so you should be able to do wsgi.WSGIServer(('0.0.0.0', 8080), app, log=app.logger)