kislyuk / Watchtower
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Watchtower: Python CloudWatch Logging
Watchtower is a log handler for Amazon Web Services CloudWatch Logs <https://aws.amazon.com/blogs/aws/cloudwatch-log-service/>
_.
CloudWatch Logs is a log management service built into AWS. It is conceptually similar to services like Splunk and Loggly, but is more lightweight, cheaper, and tightly integrated with the rest of AWS.
Watchtower, in turn, is a lightweight adapter between the Python logging system <https://docs.python.org/library/logging.html>
_ and CloudWatch Logs. It uses the boto3 AWS SDK <https://github.com/boto/boto3>
, and lets you plug your application logging directly into CloudWatch without the need
to install a system-wide log collector like awscli-cwlogs <https://pypi.python.org/pypi/awscli-cwlogs>
and round-trip
your logs through the instance's syslog. It aggregates logs into batches to avoid sending an API request per each log
message, while guaranteeing a delivery deadline (60 seconds by default).
Installation
::
pip install watchtower
Synopsis
~~~~~~~~
Install `awscli <https://pypi.python.org/pypi/awscli>`_ and set your AWS credentials (run ``aws configure``).
.. code-block:: python
import watchtower, logging
logging.basicConfig(level=logging.INFO)
logger = logging.getLogger(__name__)
logger.addHandler(watchtower.CloudWatchLogHandler())
logger.info("Hi")
logger.info(dict(foo="bar", details={}))
After running the example, you can see the log output in your `AWS console
<https://console.aws.amazon.com/cloudwatch/home>`_.
Example: Flask logging with Watchtower
.. code-block:: python
import watchtower, flask, logging
logging.basicConfig(level=logging.INFO)
app = flask.Flask("loggable")
handler = watchtower.CloudWatchLogHandler()
app.logger.addHandler(handler)
logging.getLogger("werkzeug").addHandler(handler)
@app.route('/')
def hello_world():
return 'Hello World!'
if __name__ == '__main__':
app.run()
(See also http://flask.pocoo.org/docs/errorhandling/ <http://flask.pocoo.org/docs/errorhandling/>
_.)
Example: Django logging with Watchtower
This is an example of Watchtower integration with Django. In your Django project, add the following to ``settings.py``:
.. code-block:: python
from boto3.session import Session
AWS_ACCESS_KEY_ID = 'your access key'
AWS_SECRET_ACCESS_KEY = 'your secret access key'
AWS_REGION_NAME = 'your region'
boto3_session = Session(aws_access_key_id=AWS_ACCESS_KEY_ID,
aws_secret_access_key=AWS_SECRET_ACCESS_KEY,
region_name=AWS_REGION_NAME)
LOGGING = {
'version': 1,
'disable_existing_loggers': False,
'root': {
'level': logging.ERROR,
'handlers': ['console'],
},
'formatters': {
'simple': {
'format': "%(asctime)s [%(levelname)-8s] %(message)s",
'datefmt': "%Y-%m-%d %H:%M:%S"
},
'aws': {
# you can add specific format for aws here
'format': "%(asctime)s [%(levelname)-8s] %(message)s",
'datefmt': "%Y-%m-%d %H:%M:%S"
},
},
'handlers': {
'watchtower': {
'level': 'DEBUG',
'class': 'watchtower.CloudWatchLogHandler',
'boto3_session': boto3_session,
'log_group': 'MyLogGroupName',
'stream_name': 'MyStreamName',
'formatter': 'aws',
},
},
'loggers': {
'django': {
'level': 'INFO',
'handlers': ['watchtower'],
'propagate': False,
},
# add your other loggers here...
},
}
Using this configuration, every log statement from Django will be sent to Cloudwatch in the log group ``MyLogGroupName``
under the stream name ``MyStreamName``. Instead of setting credentials via ``AWS_ACCESS_KEY_ID`` and other variables,
you can also assign an IAM role to your instance and omit those parameters, prompting boto3 to ingest credentials from
instance metadata.
(See also the `Django logging documentation <https://docs.djangoproject.com/en/dev/topics/logging/>`__).
Examples: Querying CloudWatch logs
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This section is not specific to Watchtower. It demonstrates the use of awscli and jq to read and search CloudWatch logs
on the command line.
For the Flask example above, you can retrieve your application logs with the following two commands::
aws logs get-log-events --log-group-name watchtower --log-stream-name loggable | jq '.events[].message'
aws logs get-log-events --log-group-name watchtower --log-stream-name werkzeug | jq '.events[].message'
CloudWatch Logs supports alerting and dashboards based on `metric filters
<http://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/FilterAndPatternSyntax.html>`_, which are pattern
rules that extract information from your logs and feed it to alarms and dashboard graphs.
Examples: Python Logging Config
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The Python ``logging.config`` module has the ability to provide a configuration file that can be loaded in order to
separate the logging configuration from the code.
The following are two example YAML configuration files that can be loaded using PyYAML. The resulting ``dict`` object
can then be loaded into ``logging.config.dictConfig``. The first example is a basic example that relies on the default
configuration provided by ``boto3``:
.. code-block:: yaml
# Default AWS Config
version: 1
disable_existing_loggers: False
formatters:
json:
format: "[%(asctime)s] %(process)d %(levelname)s %(name)s:%(funcName)s:%(lineno)s - %(message)s"
plaintext:
format: "[%(asctime)s] %(process)d %(levelname)s %(name)s:%(funcName)s:%(lineno)s - %(message)s"
handlers:
console:
class: logging.StreamHandler
formatter: plaintext
level: DEBUG
stream: ext://sys.stdout
logfile:
class: logging.handlers.RotatingFileHandler
formatter: plaintext
level: DEBUG
filename: watchtower.log
maxBytes: 1000000
backupCount: 3
watchtower:
class: watchtower.CloudWatchLogHandler
formatter: json
level: DEBUG
log_group: watchtower
stream_name: "{logger_name}-{strftime:%y-%m-%d}"
send_interval: 10
create_log_group: False
root:
level: DEBUG
propagate: True
handlers: [console, logfile, watchtower]
loggers:
botocore:
level: INFO
urllib3:
level: INFO
The above works well if you can use the default boto3 credential configuration, or rely on environment variables.
However, sometimes one may want to use different credentials for logging than used for other functionality;
in this case the ``boto3_profile_name`` option to Watchtower can be used to provide a boto3 profile name:
.. code-block:: yaml
# AWS Config Profile
version: 1
...
handlers:
...
watchtower:
boto3_profile_name: watchtowerlogger
...
Finally, the following shows how to load the configuration into the working application:
.. code-block:: python
import logging.config
import flask
import yaml
app = flask.Flask("loggable")
@app.route('/')
def hello_world():
return 'Hello World!'
if __name__ == '__main__':
with open('logging.yml') as log_config:
config_yml = log_config.read()
config_dict = yaml.safe_load(config_yml)
logging.config.dictConfig(config_dict)
app.run()
Boto3/botocore/urllib3 logs
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Because watchtower uses boto3 to send logs, the act of sending them generates a number of DEBUG level log messages
from boto3's dependencies, botocore and urllib3. To avoid generating a self-perpetuating stream of log messages,
``watchtower.CloudWatchLogHandler`` attaches a
`filter <https://docs.python.org/3/library/logging.html#logging.Handler.addFilter>`_ to itself which drops all DEBUG
level messages from these libraries, and drops all messages at all levels from them when shutting down (specifically,
in ``watchtower.CloudWatchLogHandler.flush()`` and ``watchtower.CloudWatchLogHandler.close()``). The filter does not
apply to any other handlers you may have processing your messages, so the following basic configuration will cause
botocore debug logs to print to stderr but not to Cloudwatch:
.. code-block:: python
import watchtower, logging
logging.basicConfig(level=logging.DEBUG)
logger = logging.getLogger()
logger.addHandler(watchtower.CloudWatchLogHandler())
Authors
~~~~~~~
* Andrey Kislyuk
Links
~~~~~
* `Project home page (GitHub) <https://github.com/kislyuk/watchtower>`_
* `Documentation <https://kislyuk.github.io/watchtower/>`_
* `Package distribution (PyPI) <https://pypi.python.org/pypi/watchtower>`_
* `AWS CLI CloudWatch Logs plugin <https://pypi.python.org/pypi/awscli-cwlogs>`_
* `Docker awslogs adapter <https://github.com/docker/docker/blob/master/daemon/logger/awslogs/cloudwatchlogs.go>`_
Bugs
~~~~
Please report bugs, issues, feature requests, etc. on `GitHub <https://github.com/kislyuk/watchtower/issues>`_.
License
~~~~~~~
Licensed under the terms of the `Apache License, Version 2.0 <http://www.apache.org/licenses/LICENSE-2.0>`_.
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