# Logging

Sanic allows you to do different types of logging (access log, error log) on the requests based on the Python logging API (opens new window). You should have some basic knowledge on Python logging if you want to create a new configuration.

# Quick Start

A simple example using default settings would be like this:

from sanic import Sanic
from sanic.log import logger
from sanic.response import text

app = Sanic('logging_example')

@app.route('/')
async def test(request):
    logger.info('Here is your log')
    return text('Hello World!')

if __name__ == "__main__":
  app.run(debug=True, access_log=True)

After the server is running, you should see logs like this.

[2021-01-04 15:26:26 +0200] [1929659] [INFO] Goin' Fast @ http://127.0.0.1:8000
[2021-01-04 15:26:26 +0200] [1929659] [INFO] Starting worker [1929659]

You can send a request to server and it will print the log messages.

[2021-01-04 15:26:28 +0200] [1929659] [INFO] Here is your log
[2021-01-04 15:26:28 +0200] - (sanic.access)[INFO][127.0.0.1:44228]: GET http://localhost:8000/  200 -1

# Changing Sanic loggers

To use your own logging config, simply use logging.config.dictConfig, or pass log_config when you initialize Sanic app.

app = Sanic('logging_example', log_config=LOGGING_CONFIG)

if __name__ == "__main__":
  app.run(access_log=False)

FYI

Logging in Python is a relatively cheap operation. However, if you are serving a high number of requests and performance is a concern, all of that time logging out access logs adds up and becomes quite expensive.

This is a good opportunity to place Sanic behind a proxy (like nginx) and to do your access logging there. You will see a significant increase in overall performance by disabling the access_log.

For optimal production performance, it is advised to run Sanic with debug and access_log disabled: app.run(debug=False, access_log=False)

# Configuration

Sanic's default logging configuration is: sanic.log.LOGGING_CONFIG_DEFAULTS.

There are three loggers used in sanic, and must be defined if you want to create your own logging configuration:

Logger Name Use Case
sanic.root Used to log inernal messages.
sanic.error Used to log error logs.
sanic.access Used to log access logs.

# Log format

In addition to default parameters provided by Python (asctime, levelname, message), Sanic provides additional parameters for access logger with.

Log Context Parameter Parameter Value Datatype
host request.ip str
request request.method + " " + request.url str
status response int
byte len(response.body) int

The default access log format is:

%(asctime)s - (%(name)s)[%(levelname)s][%(host)s]: %(request)s %(message)s %(status)d %(byte)d
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