Allow loading logging config from yaml

The newer dictConfig logging configuration allows a much more flexible
configuration and should be used in preference to the file config. For
backwards compatibility if the logging configuration has a yaml
extension then load it, otherwise fall back to the file config.

Change-Id: Ia29e294144fa057ded7b72e4475265766f855494

doc/source/installation.rst

@@ -61,6 +61,13 @@ configurations that contain sensitive data, this is currently not used, but
 may be in the future.
 
 There is an optional logging configuration file, specified with the ``-l``
-option. The logging configuration file is in the standard python logging
-`configuration file format
-<http://docs.python.org/2/library/logging.config.html#configuration-file-format>`_.
+option. The logging configuration file can accept either:
+
+* the traditional ini python logging `configuration file format
+  <https://docs.python.org/2/library/logging.config.html#configuration-file-format>`_.
+
+* a `.yml` or `.yaml` suffixed file that will be parsed and loaded as the newer
+  `dictConfig format
+  <https://docs.python.org/2/library/logging.config.html#configuration-dictionary-schema>`_.
+
+The Nodepool configuration file is described in :ref:`configuration`.

nodepool/cmd/__init__.py

@@ -26,6 +26,8 @@ import sys
 import threading
 import traceback
 
+import yaml
+
 from nodepool.version import version_info as npd_version_info
 
 
@@ -105,7 +107,12 @@ class NodepoolApp(object):
                 m = "Unable to read logging config file at %s" % fp
                 raise Exception(m)
 
-            logging.config.fileConfig(fp)
+            if os.path.splitext(fp)[1] in ('.yml', '.yaml'):
+                with open(fp, 'r') as f:
+                    logging.config.dictConfig(yaml.safe_load(f))
+
+            else:
+                logging.config.fileConfig(fp)
 
         else:
             m = '%(asctime)s %(levelname)s %(name)s: %(message)s'