Logging in production in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this Flask logging configuration?

Given the following Flask app logging setup, what will be printed to the console when a request is made?

Flask

import logging
from flask import Flask
app = Flask(__name__)

logging.basicConfig(level=logging.WARNING)

@app.route('/')
def home():
    app.logger.debug('Debug message')
    app.logger.warning('Warning message')
    return 'Hello'

if __name__ == '__main__':
    app.run()

A

[DEBUG] Debug message
[WARNING] Warning message

B [WARNING] Warning message

C No output

D [ERROR] Error message

💡 Hint

Check the logging level set by basicConfig and which messages are shown at that level.

The logging level is set to WARNING, so only WARNING and above messages are printed. DEBUG messages are ignored.

❓ Configuration

intermediate

Which logging configuration writes logs to a file with rotation in Flask?

Select the correct Flask logging setup that writes logs to a file named 'app.log' and rotates the file after it reaches 1MB, keeping 3 backups.

A

from logging.handlers import RotatingFileHandler
handler = RotatingFileHandler('app.log', maxBytes=1048576, backupCount=3)
app.logger.addHandler(handler)

B

from logging.handlers import TimedRotatingFileHandler
handler = TimedRotatingFileHandler('app.log', when='M', interval=1, backupCount=3)
app.logger.addHandler(handler)

C

handler = logging.FileHandler('app.log')
app.logger.addHandler(handler)

D

handler = logging.StreamHandler(open('app.log', 'w'))
app.logger.addHandler(handler)

💡 Hint

Look for a handler that rotates based on file size, not time.

RotatingFileHandler rotates logs based on file size. TimedRotatingFileHandler rotates based on time intervals.

❓ Troubleshoot

advanced

Why are Flask logs not appearing in production with Gunicorn?

You deployed a Flask app with Gunicorn. Your Flask app uses app.logger.warning('Test'). But no logs appear in the console or files. What is the most likely cause?

A Flask app.logger is disabled in production by default.

B The logging level is set to ERROR, so WARNING messages are ignored.

C Gunicorn does not support logging at all.

D Gunicorn overrides Flask logging and needs its own logging configuration.

💡 Hint

Consider how Gunicorn manages logging separately from Flask.

Gunicorn manages its own logging and may override or ignore Flask's logger unless configured properly.

✅ Best Practice

advanced

What is the best practice for logging sensitive information in production Flask apps?

Which option describes the best practice for handling sensitive data in logs for a Flask production app?

A Encrypt logs containing sensitive data and store them publicly.

B Log all data including sensitive info for full traceability.

C Never log sensitive data like passwords or tokens; mask or omit them if needed.

D Disable logging entirely to avoid any data leaks.

💡 Hint

Think about privacy and security risks in logs.

Logging sensitive data can cause security risks. Best practice is to avoid logging such data or mask it.

🔀 Workflow

expert

Order the steps to set up centralized logging for a Flask app in production using Docker and ELK stack.

Arrange the steps in the correct order to enable centralized logging for a Flask app running in Docker containers, sending logs to an ELK (Elasticsearch, Logstash, Kibana) stack.

A 3,1,2,4

B 1,3,2,4

C 1,2,3,4

D 3,2,1,4

💡 Hint

Think about setting up infrastructure before configuring app and forwarding logs.

First deploy ELK stack, then configure app logging format, then set Docker to forward logs, finally visualize in Kibana.