Logging configuration in FastAPI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of logging configuration with custom format

Given this FastAPI logging setup, what will be the output when a GET request is made to '/'?

FastAPI

import logging
from fastapi import FastAPI

app = FastAPI()

logging.basicConfig(level=logging.INFO, format='%(levelname)s:%(message)s')
logger = logging.getLogger(__name__)

@app.get('/')
async def root():
    logger.info('Root endpoint accessed')
    return {'message': 'Hello World'}

A INFO:root endpoint accessed

B INFO:Root endpoint accessed

C root endpoint accessed

D Logging not configured

💡 Hint

Check the logging format string and case sensitivity.

The logging format specifies level name in uppercase followed by a colon and the message. The message is exactly 'Root endpoint accessed' with capital R.

❓ Configuration

intermediate

Correct YAML logging config for rotating file handler

Which YAML snippet correctly configures a rotating file handler for FastAPI logs with max 5 files and 1MB each?

A

version: 1
handlers:
  file:
    class: logging.handlers.RotatingFileHandler
    filename: app.log
    maxBytes: 1048576
    backupCount: 5
    level: INFO
loggers:
  uvicorn:
    handlers: [file]
    level: INFO

B

version: 1
handlers:
  file:
    class: logging.FileHandler
    filename: app.log
    maxBytes: 1048576
    backupCount: 5
    level: INFO
loggers:
  uvicorn:
    handlers: [file]
    level: INFO

C

version: 1
handlers:
  file:
    class: logging.handlers.TimedRotatingFileHandler
    filename: app.log
    when: 'midnight'
    backupCount: 5
    level: INFO
loggers:
  uvicorn:
    handlers: [file]
    level: INFO

D

version: 1
handlers:
  file:
    class: logging.handlers.RotatingFileHandler
    filename: app.log
    maxBytes: 512000
    backupCount: 10
    level: INFO
loggers:
  uvicorn:
    handlers: [file]
    level: INFO

💡 Hint

RotatingFileHandler requires maxBytes and backupCount for size-based rotation.

Option A correctly uses RotatingFileHandler with maxBytes 1MB (1048576 bytes) and backupCount 5. Others either use wrong handler or wrong sizes.

❓ Troubleshoot

advanced

Why are logs missing in production with this FastAPI setup?

You configured logging in FastAPI with this code but see no logs in production. What is the most likely cause? import logging logging.basicConfig(level=logging.DEBUG) logger = logging.getLogger('uvicorn.error') logger.info('App started')

A Missing call to logger.setLevel() to enable logging

B Logging level DEBUG is too low to show info messages

C Logger name 'uvicorn.error' does not exist, so no logs are captured

D Uvicorn overrides logging config; basicConfig is ignored when running with uvicorn server

💡 Hint

Consider how uvicorn manages logging internally.

Uvicorn configures logging itself when started, so calling basicConfig in app code is ignored. Logs must be configured via uvicorn or external config.

🔀 Workflow

advanced

Order steps to enable JSON logging in FastAPI with uvicorn

Arrange these steps in the correct order to enable JSON formatted logs in a FastAPI app running with uvicorn.

A 1,2,3,4

B 1,3,2,4

C 2,1,3,4

D 3,1,2,4

💡 Hint

Think about installing dependencies before using them.

First install the package, then create the formatter, configure uvicorn to use it, and finally run uvicorn with that config.

✅ Best Practice

expert

Which logging practice improves FastAPI app observability in production?

Select the best practice that improves observability and troubleshooting in a production FastAPI app.

A Log only error messages to reduce log volume

B Log all debug messages to a single file without rotation

C Use structured logging with JSON format including request IDs and timestamps

D Disable logging to improve performance

💡 Hint

Think about how logs help in tracing and analyzing issues.

Structured JSON logs with request IDs and timestamps help correlate events and improve observability. Other options reduce usefulness or cause issues.