gocept.logging

Contents

• Advanced usage
  • Testing support
• Example configuration
  • Setup with ini file
  • Setup with ZConfig
  • syslogd configuration
  • logstash configuration
• Additional features
  • ArgumentParser
• Known bugs

This package provides infrastructure for semi-structured log messages.

This means appending easily parseable information after the free-text log message to facilitate analysis of the logs later on. The logging module of the Python standard library already has support for this, via the extra parameter. gocept.logging provides a Formatter that extracts these extra values, formats them as key=value pairs and appends them to the message:

>>> import gocept.logging
>>> import logging
>>> import sys

>>> handler = logging.StreamHandler(sys.stdout)
>>> handler.setFormatter(gocept.logging.SyslogKeyValueFormatter())
>>> log = logging.getLogger('example')
>>> log.addHandler(handler)
>>> log.warning('Hello, world!', extra={'foo': 'bar'})
Aug 24 12:10:08 localhost example: Hello, world! foo=bar

This package is tested to be compatible with Python version 2.7 and 3.3.

Advanced usage

If you have extra values that you always want to pass to your log messages (e.g things like the current user, session id, ...) you can wrap your logger with an LoggerAdapter that prefills these values. gocept.logging provides one that allows both stacking adapters and overriding the prefilled values:

>>> from gocept.logging.adapter import StaticDefaults
>>> import logging

>>> log = logging.getLogger('advanced')
>>> log = StaticDefaults(log, {'foo': 'bar', 'qux': 'baz'})
>>> log = StaticDefaults(log, {'blam': 'splat'})
>>> log.warning('Hello, world!', extra={'foo': 'override'})
    # yields {'foo': 'override', 'qux': 'baz', 'blam': 'splat'}

Testing support

To help inspecting the extra values, gocept.logging comes with a specialized handler for testing:

>>> import gocept.logging
>>> import logging

>>> log = logging.getLogger('testing')
>>> handler = gocept.logging.TestingHandler()
>>> log.addHandler(handler)
>>> log.warning('Hello, world!', extra={'foo': 'bar'})
>>> handler.messages[0].extra['foo']
'bar'

The TestingHandler records each log message as a namedtuple of type gocept.logging.testing.LogMessage so you an easily access all parts of the message.

Example configuration

Creating semi-structured log messages is the first half of the issue, while analysing them is the second half. We use logstash for that purpose.

The recommended setup is:

application -> syslogd on localhost -> logstash on central host (via UDP syslog input)

For development you might want to leave out the middle man and configure the application to send log messags via syslog protocol directly to logstash.

Setup with ini file

If you have a paste.ini for your application, you might use something like this:

[loggers]
keys = root

[handlers]
keys = console, syslog

[formatters]
keys = generic, keyvalue

[logger_root]
level = INFO
handlers = console, syslog

[handler_console]
class = StreamHandler
args = (sys.stderr,)
level = NOTSET
formatter = generic

[formatter_generic]
format = %(asctime)s %(levelname)-5.5s %(name)s: %(message)s

[handler_syslog]
class = logging.handlers.SysLogHandler
args = ()
formatter = keyvalue

[formatter_keyvalue]
class = gocept.logging.SyslogKeyValueFormatter

Setup with ZConfig

If you have a Zope application, you might use something like this:

<eventlog>
  <logfile>
    formatter zope.exceptions.log.Formatter
    format %(asctime)s %(levelname)-5.5s %(name)s: %(message)s
    path STDOUT
  </logfile>
  <syslog>
    formatter gocept.logging.SyslogKeyValueFormatter
  </syslog>
</eventlog>

syslogd configuration

rsyslog:

$EscapeControlCharactersOnReceive off
$MaxMessageSize 64k
user.* @localhost:5140

The first two lines are to support tracebacks, which are multiline and might take up some space. The last line tells rsyslogd to forward all messages of the user facility (which is what stdlib logging uses by default) via syslog UDP protocol to localhost port 5140 (where logstash might be listening).

logstash configuration

input {
        tcp {
                host => "localhost"
                port => 5140
                type => syslog
        }
        udp {
                host => "localhost"
                port => 5140
                type => syslog
        }
}

filter {
        grok {
                type => "syslog"
                pattern => [ "(?m)<%{POSINT:syslog_pri}>%{SYSLOGTIMESTAMP:syslog_timestamp} %{SYSLOGHOST:syslog_hostname} %{DATA:syslog_program}(?:\[%{POSINT:syslog_pid}\])?: %{GREEDYDATA:syslog_message}" ]
        }
        syslog_pri {
                type => "syslog"
        }
        date {
                type => "syslog"
                match => [ "syslog_timestamp", "MMM  d HH:mm:ss", "MMM dd HH:mm:ss" ]
        }
        mutate {
                type => "syslog"
                exclude_tags => "_grokparsefailure"
                replace => [ "@source_host", "%{syslog_hostname}" ]
                replace => [ "@message", "%{syslog_program}: %{syslog_message}" ]
        }
        mutate {
                type => "syslog"
                remove => [ "syslog_hostname", "syslog_timestamp" ]
        }
        kv {
                exclude_tags => "_grokparsefailure"
                type => "syslog"
        }
}

output {
        elasticsearch { embedded => true }
}

Additional features

ArgumentParser

The provided gocept.logging.ArgumentParser provides you with the ability to set a logging level in you runscripts.:

from gocept.logging import ArgumentParser
parser = ArgumentParser()
# Optionally set a custom log format, defaults to ``logging.BASIC_FORMAT``
parser.LOG_FORMAT = 'LOG:%(message)s'
# add your arguments with parser.add_argument() here
options = parser.parse_args()

Use your_run_script --help to see a help message about the arguments you can pass to set logging level.

Known bugs

If you log messages as unicode, e.g. log.info(u'foo'), the SyslogHandler will (incorrectly) prepend a byte-order mark, which confuses the logstash parser, resulting in "_grokparsefailure". This is a known bug in the Python standard library that has been fixed in Python-2.7.4.