fastapi-logging

name	fastapi-logging
description	Configure structured JSON logging with correlation IDs and request context for FastAPI

FastAPI Logging & Correlation IDs

Overview

This skill covers setting up structured JSON logging with correlation ID middleware for request tracing across the application.

Create logging.py

Create src/app/logging.py:

import logging
import sys
from typing import Any

from pythonjsonlogger import jsonlogger

from app.config import settings


class CustomJsonFormatter(jsonlogger.JsonFormatter):
    """
    Custom JSON formatter that adds standard fields to all log records.

    Output format:
    {
        "timestamp": "2025-01-05T12:00:00.000Z",
        "level": "INFO",
        "message": "Request completed",
        "logger": "app.api.v1.items",
        "correlation_id": "uuid",
        ...additional fields
    }
    """

    def add_fields(
        self,
        log_record: dict[str, Any],
        record: logging.LogRecord,
        message_dict: dict[str, Any],
    ) -> None:
        super().add_fields(log_record, record, message_dict)

        
        log_record[] = .formatTime(record, .datefmt)
        log_record[] = record.levelname
        log_record[] = record.name

        
        log_record.pop(, )
        log_record.pop(, )

        
         app.middleware.correlation_id  get_correlation_id

        correlation_id = get_correlation_id()
         correlation_id:
            log_record[] = correlation_id


 () -> :
    
    log_level = (logging, settings.log_level.upper(), logging.INFO)

    
    root_logger = logging.getLogger()
    root_logger.setLevel(log_level)

    
    root_logger.handlers.clear()

    
    handler = logging.StreamHandler(sys.stdout)
    handler.setLevel(log_level)

     settings.log_json_format:
        
        formatter = CustomJsonFormatter(
            fmt=,
            datefmt=,
        )
    :
        
        formatter = logging.Formatter(
            fmt=,
            datefmt=,
        )

    handler.setFormatter(formatter)
    root_logger.addHandler(handler)

    
    logging.getLogger().setLevel(logging.WARNING)
    logging.getLogger().setLevel(logging.WARNING)
    logging.getLogger().setLevel(
        logging.INFO  settings.database_echo  logging.WARNING
    )
    logging.getLogger().setLevel(logging.WARNING)
    logging.getLogger().setLevel(logging.WARNING)


 () -> logging.Logger:
    
     logging.getLogger(name)