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Python logging in JSON format

Published at: 2/8/2020

Logging in python can be achieved using inbuilt logging module. However, analysing the text based logs like below, can be complicated for log aggregation tools like ELK, especially in a microservice architecture

2020-07-20 12:05:30,766 - __main__ - DEBUG - This is a debug message

Alternatively, if we manage to output logs as stream of json objects with pre-defined key-values, it becomes much easier to index & analyse in an organised manner.

Required package

One such python package, which enabled Json logging for python application is https://github.com/thangbn/json-logging-python. Other similar solutions are also available.

Install

Using pip
```
pip install json-logging
```

Example setup

Create a genetic utility function to return a logger object

def get_logger():
    """
    Generic utility function to get logger object with fixed configurations
    :return:
    logger object
    """
    json_logging.ENABLE_JSON_LOGGING = True
    json_logging.init_non_web()
    logger = logging.getLogger(__name__)
    logging.basicConfig()
    json_logging.config_root_logger()
    logger.setLevel(logging.DEBUG)
    logging.addLevelName(logging.ERROR, 'error')
    logging.addLevelName(logging.WARNING, 'warning')
    logging.addLevelName(logging.INFO, 'info')
    logging.addLevelName(logging.DEBUG, 'debug')
    logger.addHandler(logging.NullHandler())
    return logger

Create a logger object
```
logger = get_logger()
```
Sample log generation code & output

logger.error(e)

{"written_at": "2020-08-01T19:39:45.359Z", "written_ts": 1596310785359963000, "msg": "Internal Server Error: /api/endpoint1/user_name", "type": "log", "logger": "django.request", "thread": "Thread-3", "level": "error", "module": "log", "line_no": 228, "exc_info": "Traceback (most recent call last):\n...", "filename": "log.py"}

Ideas for advanced use

In addition to general logs, we can also use log messages with custom key-values for specific insights about the application. For example, we can add some extra keys to keep track of inter-api response time & use it afterwards to understand application performance.

logger.info("Fetched from apiA/search",
                       extra={'props':
                           {
                               'caller_api': 'apiA',
                               'receiver_api': 'apiB',
                               'receiver_endpoint': 'search',
                               'api_response_parsed_duration': 28
                           }
                       }
            )

Conclusion

As json is one of the most flexible, portable & understandable data transfer format, it can provide immense benefit to use json logging for any application (including python).

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