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diff --git a/doc/rtd/topics/logging.rst b/doc/rtd/topics/logging.rst new file mode 100644 index 00000000..b010aa96 --- /dev/null +++ b/doc/rtd/topics/logging.rst @@ -0,0 +1,175 @@ +======= +Logging +======= +Cloud-init supports both local and remote logging configurable through python's +built-in logging configuration and through the cloud-init rsyslog module. + +Command Output +-------------- +Cloud-init can redirect its stdout and stderr based on config given under the +``output`` config key. The output of any commands run by cloud-init and any +user or vendor scripts provided will also be included here. The ``output`` +key accepts a dictionary for configuration. Output files may be specified +individually for each stage (``init``, ``config``, and ``final``), or a single +key ``all`` may be used to specify output for all stages. + +The output for each stage may be specified as a dictionary of ``output`` and +``error`` keys, for stdout and stderr respectively, as a tuple with stdout +first and stderr second, or as a single string to use for both. The strings +passed to all of these keys are handled by the system shell, so any form of +redirection that can be used in bash is valid, including piping cloud-init's +output to ``tee``, or ``logger``. If only a filename is provided, cloud-init +will append its output to the file as though ``>>`` was specified. + +By default, cloud-init loads its output configuration from +``/etc/cloud/coud.cfg.d/05_logging.cfg``. The default config directs both +stdout and stderr from all cloud-init stages to +``/var/log/cloud-init-output.log``. The default config is given as :: + + output: { all: "| tee -a /var/log/cloud-init-output.log" } + +For a more complex example, the following configuration would output the init +stage to ``/var/log/cloud-init.out`` and ``/var/log/cloud-init.err``, for +stdout and stderr respectively, replacing anything that was previously there. +For the config stage, it would pipe both stdout and stderr through +``tee -a /var/log/cloud-config.log``. For the final stage it would append the +output of stdout and stderr to ``/var/log/cloud-final.out`` and +``/var/log/cloud-final.err`` respectively. :: + + output: + init: + output: "> /var/log/cloud-init.out" + error: "> /var/log/cloud-init.err" + config: "tee -a /var/log/cloud-config.log" + final: + - ">> /var/log/cloud-final.out" + - "/var/log/cloud-final.err" + +Python Logging +-------------- +Cloud-init uses the python logging module, and can accept config for this +module using the standard python fileConfig format. Cloud-init looks for config +for the logging module under the ``logcfg`` key. + +.. note:: + the logging configuration is not yaml, it is python ``fileConfig`` format, + and is passed through directly to the python logging module. please use the + correct syntax for a multi-line string in yaml. + +By default, cloud-init uses the logging configuration provided in +``/etc/cloud/cloud.cfg.d/05_logging.cfg``. The default python logging +configuration writes all cloud-init events with a priority of ``WARNING`` or +higher to console, and writes all events with a level of ``DEBUG`` or higher +to ``/var/log/cloud-init.log`` and via syslog. + +Python's fileConfig format consists of sections with headings in the format +``[title]`` and key value pairs in each section. Configuration for python +logging must contain the sections ``[loggers]``, ``[handlers]``, and +``[formatters]``, which name the entities of their respective types that will +be defined. The section name for each defined logger, handler and formatter +will start with its type, followed by an underscore (``_``) and the name of the +entity. For example, if a logger was specified with the name ``log01``, config +for the logger would be in the section ``[logger_log01]``. + +Logger config entries contain basic logging set up. They may specify a list of +handlers to send logging events to as well as the lowest priority level of +events to handle. A logger named ``root`` must be specified and its +configuration (under ``[logger_root]``) must contain a level and a list of +handlers. A level entry can be any of the following: ``DEBUG``, ``INFO``, +``WARNING``, ``ERROR``, ``CRITICAL``, or ``NOTSET``. For the ``root`` logger +the ``NOTSET`` option will allow all logging events to be recorded. + +Each configured handler must specify a class under the python's ``logging`` +package namespace. A handler may specify a message formatter to use, a priority +level, and arguments for the handler class. Common handlers are +``StreamHandler``, which handles stream redirects (i.e. logging to stderr), +and ``FileHandler`` which outputs to a log file. The logging module also +supports logging over net sockets, over http, via smtp, and additional +complex configurations. For full details about the handlers available for +python logging, please see the documentation for `python logging handlers`_. + +Log messages are formatted using the ``logging.Formatter`` class, which is +configured using ``formatter`` config entities. A default format of +``%(message)s`` is given if no formatter configs are specified. Formatter +config entities accept a format string which supports variable replacements. +These may also accept a ``datefmt`` string which may be used to configure the +timestamp used in the log messages. The format variables ``%(asctime)s``, +``%(levelname)s`` and ``%(message)s`` are commonly used and represent the +timestamp, the priority level of the event and the event message. For +additional information on logging formatters see `python logging formatters`_. + +.. note:: + by default the format string used in the logging formatter are in python's + old style ``%s`` form. the ``str.format()`` and ``string.Template`` styles + can also be used by using ``{`` or ``$`` in place of ``%`` by setting the + ``style`` parameter in formatter config. + +A simple, but functional python logging configuration for cloud-init is below. +It will log all messages of priority ``DEBUG`` or higher both stderr and +``/tmp/my.log`` using a ``StreamHandler`` and a ``FileHandler``, using +the default format string ``%(message)s``:: + + logcfg: | + [loggers] + keys=root,cloudinit + [handlers] + keys=ch,cf + [formatters] + keys= + [logger_root] + level=DEBUG + handlers= + [logger_cloudinit] + level=DEBUG + qualname=cloudinit + handlers=ch,cf + [handler_ch] + class=StreamHandler + level=DEBUG + args=(sys.stderr,) + [handler_cf] + class=FileHandler + level=DEBUG + args=('/tmp/my.log',) + +For additional information about configuring python's logging module, please +see the documentation for `python logging config`_. + +Rsyslog Module +-------------- +Cloud-init's ``cc_rsyslog`` module allows for fully customizable rsyslog +configuration under the ``rsyslog`` config key. The simplest way to +use the rsyslog module is by specifying remote servers under the ``remotes`` +key in ``rsyslog`` config. The ``remotes`` key takes a dictionary where each +key represents the name of an rsyslog server and each value is the +configuration for that server. The format for server config is: + + - optional filter for log messages (defaults to ``*.*``) + - optional leading ``@`` or ``@@``, indicating udp and tcp respectively + (defaults to ``@``, for udp) + - ipv4 or ipv6 hostname or address. ipv6 addresses must be in ``[::1]`` + format, (e.g. ``@[fd00::1]:514``) + - optional port number (defaults to ``514``) + +For example, to send logging to an rsyslog server named ``log_serv`` with +address ``10.0.4.1``, using port number ``514``, over udp, with all log +messages enabled one could use either of the following. + +With all options specified:: + + rsyslog: + remotes: + log_serv: "*.* @10.0.4.1:514" + +With defaults used:: + + rsyslog: + remotes: + log_serv: "10.0.4.1" + + +For more information on rsyslog configuration, see :ref:`cc_rsyslog`. + +.. _python logging config: https://docs.python.org/3/library/logging.config.html#configuration-file-format +.. _python logging handlers: https://docs.python.org/3/library/logging.handlers.html +.. _python logging formatters: https://docs.python.org/3/library/logging.html#formatter-objects |