FileNotFoundError on Heroku after creating that file

Question

My app has some additional logging, it works fine on a local machine and even on Heroku local. When I push it to Heroku, it raises a FileNotFoundError . Here is my code:

class Logger:
    def __init__(self, name, file_handler, formatter, stream_handler):
        if not os.path.exists('Logs'):
            os.makedirs('Logs')

        self.logger = logging.getLogger(name)
        self.logger.setLevel(logging.DEBUG)

        file_handler.setFormatter(formatter)
        self.logger.addHandler(file_handler)

        if stream_handler:
            stream_handler = logging.StreamHandler()
            stream_handler.setFormatter(formatter)
            self.logger.addHandler(stream_handler)


logger_dev = Logger('dev',
                    handlers.TimedRotatingFileHandler(f'Logs/dev.log', when='midnight', backupCount=2),
                    logging.Formatter('%(asctime)s : %(levelname)s : %(filename)s : %(funcName)s : %(message)s'),
                    True)

logger_usr = Logger('usr',
                    handlers.RotatingFileHandler(f'Logs/usr.log', maxBytes=7 * 1024 * 1024, backupCount=2),
                    logging.Formatter('%(asctime)s : %(message)s'),
                    False)

I've also tried explicitly creating .log files by adding this to the Logger class:

if not os.path.exists(f'Logs/{name}.log'):
    open(f'Logs/{name}.log', 'w+').close()

Here are Heroku logs:

2020-06-15T20:59:43.441969+00:00 app[worker.1]: Traceback (most recent call last):
2020-06-15T20:59:43.441997+00:00 app[worker.1]: File "bot.py", line 8, in <module>
2020-06-15T20:59:43.442110+00:00 app[worker.1]: import settings as s
2020-06-15T20:59:43.442114+00:00 app[worker.1]: File "/app/settings.py", line 60, in <module>
2020-06-15T20:59:43.442251+00:00 app[worker.1]: handlers.TimedRotatingFileHandler(f'Logs/dev.log', when='midnight', backupCount=2),
2020-06-15T20:59:43.442254+00:00 app[worker.1]: File "/app/.heroku/python/lib/python3.8/logging/handlers.py", line 200, in __init__
2020-06-15T20:59:43.442437+00:00 app[worker.1]: BaseRotatingHandler.__init__(self, filename, 'a', encoding, delay)
2020-06-15T20:59:43.442439+00:00 app[worker.1]: File "/app/.heroku/python/lib/python3.8/logging/handlers.py", line 55, in __init__
2020-06-15T20:59:43.442606+00:00 app[worker.1]: logging.FileHandler.__init__(self, filename, mode, encoding, delay)
2020-06-15T20:59:43.442622+00:00 app[worker.1]: File "/app/.heroku/python/lib/python3.8/logging/__init__.py", line 1143, in __init__
2020-06-15T20:59:43.443050+00:00 app[worker.1]: StreamHandler.__init__(self, self._open())
2020-06-15T20:59:43.443054+00:00 app[worker.1]: File "/app/.heroku/python/lib/python3.8/logging/__init__.py", line 1172, in _open
2020-06-15T20:59:43.443475+00:00 app[worker.1]: return open(self.baseFilename, self.mode, encoding=self.encoding)
2020-06-15T20:59:43.443501+00:00 app[worker.1]: FileNotFoundError: [Errno 2] No such file or directory: '/app/Logs/dev.log'

Answer 1

Don't log to files on Heroku. Its ephemeral filesystem means that anything you write could be lost at any time, and will be lost at least daily.

Instead, log to stderr or stdout . Then Heroku can incorporate your logs into its log stream :

A Heroku app's logs are aggregated from the output streams of all of its running processes, system components, and backing services

Logs are mostly transient on Heroku, so you might want to set up a logging addon or log drain :

The logs command retrieves 100 log lines by default. You can specify the number of log lines to retrieve (up to a maximum of 1,500 lines) by using the --num (or -n ) option.