Add documentation about shade's use of logging

shade logs to some specific named loggers for various things. They are
defined and intentional, but are not documented. So let's document them.

Change-Id: If52553e5478d4e2f8a56f5d899e93fd2b4fe3c2d

doc/source/index.rst

@@ -13,6 +13,7 @@ Contents:
 
    installation
    usage
+   logging
    model
    contributing
    coding

doc/source/logging.rst

@@ -0,0 +1,98 @@
+=======
+Logging
+=======
+
+`shade` uses `Python Logging`_. As `shade` is a library, it does not
+configure logging handlers automatically, expecting instead for that to be
+the purview of the consuming application.
+
+Simple Usage
+------------
+
+For consumers who just want to get a basic logging setup without thinking
+about it too deeply, there is a helper method. If used, it should be called
+before any other `shade` functionality.
+
+.. code-block:: python
+
+  import shade
+  shade.simple_logging()
+
+`shade.simple_logging` takes two optional boolean arguments:
+
+debug
+  Turns on debug logging.
+
+http_debug
+  Turns on debug logging as well as debug logging of the underlying HTTP calls.
+
+`shade.simple_logging` also sets up a few other loggers and squelches some
+warnings or log messages that are otherwise uninteresting or unactionable by
+a `shade` user.
+
+Advanced Usage
+--------------
+
+`shade` logs to a set of different named loggers.
+
+Most of the logging is set up to log to the root `shade` logger. There are
+additional sub-loggers that are used at times, primarily so that a user can
+decide to turn on or off a specific type of logging. They are listed below.
+
+shade.task_manager
+  `shade` uses a Task Manager to perform remote calls. The `shade.task_manager`
+  logger emits messages at the start and end of each Task announging what
+  it is going to run and then what it ran and how long it took. Logging
+  `shade.task_manager` is a good way to get a trace of external actions shade
+  is taking without full `HTTP Tracing`_.
+
+shade.request_ids
+  The `shade.request_ids` logger emits a log line at the end of each HTTP
+  interaction with the OpenStack Request ID associated with the interaction.
+  This can be be useful for tracking action taken on the server-side if one
+  does not want `HTTP Tracing`_.
+
+shade.exc
+  If `log_inner_exceptions` is set to True, `shade` will emit any wrapped
+  exception to the `shade.exc` logger. Wrapped exceptions are usually
+  considered implementation details, but can be useful for debugging problems.
+
+shade.iterate_timeout
+  When `shade` needs to poll a resource, it does so in a loop that waits
+  between iterations and ultimately timesout. The `shade.iterate_timeout`
+  logger emits messages for each iteration indicating it is waiting and for
+  how long. These can be useful to see for long running tasks so that one
+  can know things are not stuck, but can also be noisy.
+
+shade.http
+  `shade` will sometimes log additional information about HTTP interactions
+  to the `shade.http` logger. This can be verbose, as it sometimes logs
+  entire response bodies.
+
+shade.fnmatch
+  `shade` will try to use `fnmatch`_ on given `name_or_id` arguments. It's a
+  best effort attempt, so pattern misses are logged to `shade.fnmatch`. A user
+  may not be intending to use an fnmatch pattern - such as if they are trying
+  to find an image named ``Fedora 24 [official]``, so these messages are
+  logged separately.
+
+.. _fnmatch: https://pymotw.com/2/fnmatch/
+
+HTTP Tracing
+------------
+
+HTTP Interactions are handled by `keystoneauth`. If you want to enable HTTP
+tracing while using `shade` and are not using `shade.simple_logging`,
+set the log level of the `keystoneauth` logger to `DEBUG`.
+
+Python Logging
+--------------
+
+Python logging is a standard feature of Python and is documented fully in the
+Python Documentation, which varies by version of Python.
+
+For more information on Python Logging for Python v2, see
+https://docs.python.org/2/library/logging.html.
+
+For more information on Python Logging for Python v3, see
+https://docs.python.org/3/library/logging.html.