日志

日志管理快速入门

Django 使用 Python 内置的 logging 模块处理系统日志。关于该模块的使用,Python 自己的文档里有更详细的探讨。不过,如果你从来没用过 Python 的 logging 框架(或者即便你用过),这里是一篇快速的入门讲解。

日志框架的组成元素

一份 Python logging 配置有下面四个部分组成:

Loggers

logger 是日志系统的入口。每个 logger 都是命名了的 bucket, 消息写入 bucket 以便进一步处理。

logger 可以配置 日志级别。日志级别描述了由该 logger 处理的消息的严重性。Python 定义了下面几种日志级别:

  • DEBUG:排查故障时使用的低级别系统信息
  • INFO:一般的系统信息
  • WARNING:描述系统发生了一些小问题的信息
  • ERROR:描述系统发生了大问题的信息
  • CRITICAL:描述系统发生严重问题的信息

每一条写入 logger 的消息都是一条*日志记录*。每一条日志记录也包含*日志级别*,代表对应消息的严重程度。日志记录还包含有用的元数据,来描述被记录了日志的事件细节,例如堆栈跟踪或者错误码。

当 logger 处理一条消息时,会将自己的日志级别和这条消息的日志级别做对比。如果消息的日志级别匹配或者高于 logger 的日志级别,它就会被进一步处理。否则这条消息就会被忽略掉。

当 logger 确定了一条消息需要处理之后,会把它传给 Handler

Handlers

Handler 是决定如何处理 logger 中每一条消息的引擎。它描述特定的日志行为,比如把消息输出到屏幕、文件或网络 socket。

和 logger 一样,handler 也有日志级别的概念。如果一条日志记录的级别不匹配或者低于 handler 的日志级别,对应的消息会被 handler 忽略。

一个 logger 可以有多个 handler,每一个 handler 可以有不同的日志级别。这样就可以根据消息的重要性不同,来提供不同格式的输出。例如,你可以添加一个 handler 把 ERRORCRITICAL 消息发到寻呼机,再添加另一个 handler 把所有的消息(包括 ERRORCRITICAL 消息)保存到文件里以便日后分析。

过滤器

在日志记录从 logger 传到 handler 的过程中,使用 Filter 来做额外的控制。

默认情况下,只要级别匹配,任何日志消息都会被处理。不过,也可以通过添加 filter 来给日志处理的过程增加额外条件。例如,可以添加一个 filter 只允许某个特定来源的 ERROR 消息输出。

Filter 还被用来在日志输出之前对日志记录做修改。例如,可以写一个 filter,当满足一定条件时,把日志记录从 ERROR 降到 WARNING 级别。

Filter 在 logger 和 handler 中都可以添加;多个 filter 可以链接起来使用,来做多重过滤操作。

Formatters

日志记录最终是需要以文本来呈现的。Formatter 描述了文本的格式。一个 formatter 通常由包含 :ref:`LogRecord attributes `<python:logrecord-attributes> 的 Python 格式化字符串组成,不过你也可以为特定的格式来配置自定义的 formatter。

使用 logging 模块

配置好了 logger,handler,filter 和 formatter 之后,需要在代码里发起 logging 的调用。使用 logging 框架非常简单,下面是个例子:

# import the logging library
import logging

# Get an instance of a logger
logger = logging.getLogger(__name__)

def my_view(request, arg1, arg):
    ...
    if bad_mojo:
        # Log an error message
        logger.error('Something went wrong!')

就这么简单!bad_mojo 条件每次满足都会写一条 error 日志。

为 logger 命名

logging.getLogger() 的调用会获取(必要时会创建)一个 logger 的实例。不同的 logger 实例用名字来区分。这个名字是为了在配置的时候指定 logger。

按照惯例,logger 的名字通常是包含该 logger 的 Python 模块名,即 __name__。这样可以基于模块来过滤和处理日志请求。不过,如果你有其他的方式来组织你的日志消息,可以为 logger 提供点号分割的名字来标识它:

# Get an instance of a specific named logger
logger = logging.getLogger('project.interesting.stuff')

这种 logger 的名字,用点号分隔的路径定义了一种层次结构。project.interesting 这个 logger 是 project.interesting.stuff logger 的上级;而 project logger 是 project.interesting logger 的上级。

为什么这种层级结构是重要的呢?因为 logger 可以设置为将日志的请求*传播*给上级。这样就可以在 logger 树结构的顶层定义一组单独的 handler,来捕获所有下层的日志请求。在 project 命名空间中定义的 logger handler 将会捕获 project.interestingproject.interesting.stuff 这两个 logger 中的所有日志请求。

可以基于 logger 来控制传播的行为。 如果你不希望某个 logger 传播给上级,可以关闭它。

发起 logging 调用

logger 实例包含了每种默认日志级别的入口方法:

  • logger.debug()
  • logger.info()
  • logger.warning()
  • logger.error()
  • logger.critical()

还有两种其他的调用方法:

  • logger.log():手动输出一条指定日志级别的日志消息。
  • logger.exception():创建一个包含当前异常堆栈帧的 ERROR 级别日志消息。

日志模块的配置

当然,仅仅在代码里调用 logging 是不够的。还需要配置 logger、handler、filter 和 formatter 来确保日志框架能有效地输出日志。

Python 的日志库提供了一些配置方法,可以使用编程接口或者配置文件。Django默认使用 dictConfig format

为了配置 logging ,用字典的格式定义一个 LOGGING 配置项,这些配置描述了你想要的 logger、handler、filter 和 formatter,以及它们的日志级别和其他你想要的属性。

默认情况下 LOGGING 配置和 Django's default logging configuration 按照下面的方式合并在一起:

如果 LOGGING 这个配置项中的 disable_existing_loggers 被设置为 True (默认就是 Ture),那么默认配置中的 logger 全部被禁用。被禁用的 logger 并不是被删除了,它们仍然存在,只是静默地丢弃所有发来的日志请求,甚至不会传播给上级 logger。所以你要谨慎使用 'disable_existing_loggers': True;这很可能不是你想要的。相反你应该把 disable_existing_loggers 设置为 False,然后再重新定义其中的一些默认 loggers,或者你也可以将 LOGGING_CONFIG 设置为 None 然后 handle logging config yourself

logging 被配置成了 Django setup() 函数的一部分。因此,你可以确定的是,logger 一直都可以在项目代码里使用。

示例

The full documentation for dictConfig format is the best source of information about logging configuration dictionaries. However, to give you a taste of what is possible, here are several examples.

First, here's a simple configuration which writes all logging from the django logger to a local file:

LOGGING = {
    'version': 1,
    'disable_existing_loggers': False,
    'handlers': {
        'file': {
            'level': 'DEBUG',
            'class': 'logging.FileHandler',
            'filename': '/path/to/django/debug.log',
        },
    },
    'loggers': {
        'django': {
            'handlers': ['file'],
            'level': 'DEBUG',
            'propagate': True,
        },
    },
}

If you use this example, be sure to change the 'filename' path to a location that's writable by the user that's running the Django application.

Second, here's an example of how to make the logging system print Django's logging to the console. It may be useful during local development.

By default, this config only sends messages of level INFO or higher to the console (same as Django's default logging config, except that the default only displays log records when DEBUG=True). Django does not log many such messages. With this config, however, you can also set the environment variable DJANGO_LOG_LEVEL=DEBUG to see all of Django's debug logging which is very verbose as it includes all database queries:

import os

LOGGING = {
    'version': 1,
    'disable_existing_loggers': False,
    'handlers': {
        'console': {
            'class': 'logging.StreamHandler',
        },
    },
    'loggers': {
        'django': {
            'handlers': ['console'],
            'level': os.getenv('DJANGO_LOG_LEVEL', 'INFO'),
        },
    },
}

Finally, here's an example of a fairly complex logging setup:

LOGGING = {
    'version': 1,
    'disable_existing_loggers': False,
    'formatters': {
        'verbose': {
            'format': '{levelname} {asctime} {module} {process:d} {thread:d} {message}',
            'style': '{',
        },
        'simple': {
            'format': '{levelname} {message}',
            'style': '{',
        },
    },
    'filters': {
        'special': {
            '()': 'project.logging.SpecialFilter',
            'foo': 'bar',
        },
        'require_debug_true': {
            '()': 'django.utils.log.RequireDebugTrue',
        },
    },
    'handlers': {
        'console': {
            'level': 'INFO',
            'filters': ['require_debug_true'],
            'class': 'logging.StreamHandler',
            'formatter': 'simple'
        },
        'mail_admins': {
            'level': 'ERROR',
            'class': 'django.utils.log.AdminEmailHandler',
            'filters': ['special']
        }
    },
    'loggers': {
        'django': {
            'handlers': ['console'],
            'propagate': True,
        },
        'django.request': {
            'handlers': ['mail_admins'],
            'level': 'ERROR',
            'propagate': False,
        },
        'myproject.custom': {
            'handlers': ['console', 'mail_admins'],
            'level': 'INFO',
            'filters': ['special']
        }
    }
}

This logging configuration does the following things:

  • Identifies the configuration as being in 'dictConfig version 1' format. At present, this is the only dictConfig format version.

  • Defines two formatters:

    • simple, that just outputs the log level name (e.g., DEBUG) and the log message.

      The format string is a normal Python formatting string describing the details that are to be output on each logging line. The full list of detail that can be output can be found in Formatter Objects.

    • verbose, that outputs the log level name, the log message, plus the time, process, thread and module that generate the log message.

  • Defines two filters:

    • project.logging.SpecialFilter, using the alias special. If this filter required additional arguments, they can be provided as additional keys in the filter configuration dictionary. In this case, the argument foo will be given a value of bar when instantiating SpecialFilter.
    • django.utils.log.RequireDebugTrue, which passes on records when DEBUG is True.
  • Defines two handlers:

    • console, a StreamHandler, which prints any INFO (or higher) message to sys.stderr. This handler uses the simple output format.
    • mail_admins, an AdminEmailHandler, which emails any ERROR (or higher) message to the site ADMINS. This handler uses the special filter.
  • Configures three loggers:

    • django, which passes all messages to the console handler.
    • django.request, which passes all ERROR messages to the mail_admins handler. In addition, this logger is marked to not propagate messages. This means that log messages written to django.request will not be handled by the django logger.
    • myproject.custom, which passes all messages at INFO or higher that also pass the special filter to two handlers -- the console, and mail_admins. This means that all INFO level messages (or higher) will be printed to the console; ERROR and CRITICAL messages will also be output via email.

Custom logging configuration

If you don't want to use Python's dictConfig format to configure your logger, you can specify your own configuration scheme.

The LOGGING_CONFIG setting defines the callable that will be used to configure Django's loggers. By default, it points at Python's logging.config.dictConfig() function. However, if you want to use a different configuration process, you can use any other callable that takes a single argument. The contents of LOGGING will be provided as the value of that argument when logging is configured.

Disabling logging configuration

If you don't want to configure logging at all (or you want to manually configure logging using your own approach), you can set LOGGING_CONFIG to None. This will disable the configuration process for Django's default logging. Here's an example that disables Django's logging configuration and then manually configures logging:

settings.py
LOGGING_CONFIG = None

import logging.config
logging.config.dictConfig(...)

Setting LOGGING_CONFIG to None only means that the automatic configuration process is disabled, not logging itself. If you disable the configuration process, Django will still make logging calls, falling back to whatever default logging behavior is defined.

Django's logging extensions

Django provides a number of utilities to handle the unique requirements of logging in Web server environment.

Loggers

Django provides several built-in loggers.

django

The catch-all logger for messages in the django hierarchy. No messages are posted using this name but instead using one of the loggers below.

django.request

Log messages related to the handling of requests. 5XX responses are raised as ERROR messages; 4XX responses are raised as WARNING messages. Requests that are logged to the django.security logger aren't logged to django.request.

Messages to this logger have the following extra context:

  • status_code: The HTTP response code associated with the request.
  • request: The request object that generated the logging message.

django.server

Log messages related to the handling of requests received by the server invoked by the runserver command. HTTP 5XX responses are logged as ERROR messages, 4XX responses are logged as WARNING messages, and everything else is logged as INFO.

Messages to this logger have the following extra context:

  • status_code: The HTTP response code associated with the request.
  • request: The request object that generated the logging message.

django.template

Log messages related to the rendering of templates.

  • Missing context variables are logged as DEBUG messages.

django.db.backends

Messages relating to the interaction of code with the database. For example, every application-level SQL statement executed by a request is logged at the DEBUG level to this logger.

Messages to this logger have the following extra context:

  • duration: The time taken to execute the SQL statement.
  • sql: The SQL statement that was executed.
  • params: The parameters that were used in the SQL call.

For performance reasons, SQL logging is only enabled when settings.DEBUG is set to True, regardless of the logging level or handlers that are installed.

This logging does not include framework-level initialization (e.g. SET TIMEZONE) or transaction management queries (e.g. BEGIN, COMMIT, and ROLLBACK). Turn on query logging in your database if you wish to view all database queries.

django.security.*

The security loggers will receive messages on any occurrence of SuspiciousOperation and other security-related errors. There is a sub-logger for each subtype of security error, including all SuspiciousOperations. The level of the log event depends on where the exception is handled. Most occurrences are logged as a warning, while any SuspiciousOperation that reaches the WSGI handler will be logged as an error. For example, when an HTTP Host header is included in a request from a client that does not match ALLOWED_HOSTS, Django will return a 400 response, and an error message will be logged to the django.security.DisallowedHost logger.

These log events will reach the django logger by default, which mails error events to admins when DEBUG=False. Requests resulting in a 400 response due to a SuspiciousOperation will not be logged to the django.request logger, but only to the django.security logger.

To silence a particular type of SuspiciousOperation, you can override that specific logger following this example:

'handlers': {
    'null': {
        'class': 'logging.NullHandler',
    },
},
'loggers': {
    'django.security.DisallowedHost': {
        'handlers': ['null'],
        'propagate': False,
    },
},

Other django.security loggers not based on SuspiciousOperation are:

django.db.backends.schema

Logs the SQL queries that are executed during schema changes to the database by the migrations framework. Note that it won't log the queries executed by RunPython. Messages to this logger have params and sql in their extra context (but unlike django.db.backends, not duration). The values have the same meaning as explained in django.db.backends.

Handlers

Django provides one log handler in addition to those provided by the Python logging module.

class AdminEmailHandler(include_html=False, email_backend=None)[源代码]

This handler sends an email to the site ADMINS for each log message it receives.

If the log record contains a request attribute, the full details of the request will be included in the email. The email subject will include the phrase "internal IP" if the client's IP address is in the INTERNAL_IPS setting; if not, it will include "EXTERNAL IP".

If the log record contains stack trace information, that stack trace will be included in the email.

The include_html argument of AdminEmailHandler is used to control whether the traceback email includes an HTML attachment containing the full content of the debug Web page that would have been produced if DEBUG were True. To set this value in your configuration, include it in the handler definition for django.utils.log.AdminEmailHandler, like this:

'handlers': {
    'mail_admins': {
        'level': 'ERROR',
        'class': 'django.utils.log.AdminEmailHandler',
        'include_html': True,
    }
},

Note that this HTML version of the email contains a full traceback, with names and values of local variables at each level of the stack, plus the values of your Django settings. This information is potentially very sensitive, and you may not want to send it over email. Consider using something such as Sentry to get the best of both worlds -- the rich information of full tracebacks plus the security of not sending the information over email. You may also explicitly designate certain sensitive information to be filtered out of error reports -- learn more on Filtering error reports.

By setting the email_backend argument of AdminEmailHandler, the email backend that is being used by the handler can be overridden, like this:

'handlers': {
    'mail_admins': {
        'level': 'ERROR',
        'class': 'django.utils.log.AdminEmailHandler',
        'email_backend': 'django.core.mail.backends.filebased.EmailBackend',
    }
},

By default, an instance of the email backend specified in EMAIL_BACKEND will be used.

send_mail(subject, message, *args, **kwargs)[源代码]

Sends emails to admin users. To customize this behavior, you can subclass the AdminEmailHandler class and override this method.

过滤器

Django provides some log filters in addition to those provided by the Python logging module.

class CallbackFilter(callback)[源代码]

This filter accepts a callback function (which should accept a single argument, the record to be logged), and calls it for each record that passes through the filter. Handling of that record will not proceed if the callback returns False.

For instance, to filter out UnreadablePostError (raised when a user cancels an upload) from the admin emails, you would create a filter function:

from django.http import UnreadablePostError

def skip_unreadable_post(record):
    if record.exc_info:
        exc_type, exc_value = record.exc_info[:2]
        if isinstance(exc_value, UnreadablePostError):
            return False
    return True

and then add it to your logging config:

'filters': {
    'skip_unreadable_posts': {
        '()': 'django.utils.log.CallbackFilter',
        'callback': skip_unreadable_post,
    }
},
'handlers': {
    'mail_admins': {
        'level': 'ERROR',
        'filters': ['skip_unreadable_posts'],
        'class': 'django.utils.log.AdminEmailHandler'
    }
},
class RequireDebugFalse[源代码]

This filter will only pass on records when settings.DEBUG is False.

This filter is used as follows in the default LOGGING configuration to ensure that the AdminEmailHandler only sends error emails to admins when DEBUG is False:

'filters': {
    'require_debug_false': {
        '()': 'django.utils.log.RequireDebugFalse',
    }
},
'handlers': {
    'mail_admins': {
        'level': 'ERROR',
        'filters': ['require_debug_false'],
        'class': 'django.utils.log.AdminEmailHandler'
    }
},
class RequireDebugTrue[源代码]

This filter is similar to RequireDebugFalse, except that records are passed only when DEBUG is True.

Django's default logging configuration

By default, Django configures the following logging:

When DEBUG is True:

  • The django logger sends messages in the django hierarchy (except django.server) at the INFO level or higher to the console.

When DEBUG is False:

  • The django logger sends messages in the django hierarchy (except django.server) with ERROR or CRITICAL level to AdminEmailHandler.

Independent of the value of DEBUG:

  • The django.server logger sends messages at the INFO level or higher to the console.

All loggers except django.server propagate logging to their parents, up to the root django logger. The console and mail_admins handlers are attached to the root logger to provide the behavior described above.

See also Configuring logging to learn how you can complement or replace this default logging configuration.