Use mozlog for application logging

Configure the application to use the mozlog structured log format for
 application-level log messages (log messages from libraries and
 frameworks still go through the Python Standard Library string logger).

Author: mars-f

landoapi/app.py

@@ -5,14 +5,20 @@
 
 import click
 import connexion
+import logging
 
 from connexion.resolver import RestyResolver
 from landoapi.dockerflow import dockerflow
 from landoapi.models.storage import alembic, db
+from mozlogging import MozLogFormatter
+
+logger = logging.getLogger(__name__)
 
 
 def create_app(version_path):
     """Construct an application instance."""
+    initialize_logging()
+
     app = connexion.App(__name__, specification_dir='spec/')
     app.add_api('swagger.yml', resolver=RestyResolver('landoapi.api'))
 
@@ -36,6 +42,42 @@ def create_app(version_path):
     return app
 
 
+def initialize_logging():
+    """Initialize application-wide logging."""
+    mozlog_handler = logging.StreamHandler()
+    mozlog_handler.setFormatter(MozLogFormatter())
+
+    # We need to configure the logger just for our application code.  This is
+    # because the MozLogFormatter changes the signature of the standard
+    # library logging functions.  Any code that tries to log a message assuming
+    # the standard library's formatter is in place, such as the code in the
+    # libraries we use, with throw an error if the MozLogFormatter tries to
+    # handle the message.
+    app_logger = logging.getLogger('landoapi')
+
+    app_logger.addHandler(mozlog_handler)
+
+    app_logger.setLevel(log_level_from_environ())
+
+    logger.debug({'msg': 'logging initialized'}, 'debug')
+
+
+def log_level_from_environ():
+    """Read the operator's desired log level from the LOG_LEVEL env var.
+
+    The log level string can be lowercase or uppercase.  The string must be
+    one of the levels from the Python Standard Library's logging library.
+    Defaults to logging.INFO if the environment variable is not set.
+
+    Returns the logging.LEVEL object for the level that was read.  Raises an
+    exception if the given log level is not one of the Python Standard
+    Library's log levels.
+    """
+    level_str = os.environ.get('LOG_LEVEL', 'INFO')
+    # getattr() raises an exception if the requested log level doesn't exist.
+    return getattr(logging, level_str.upper())
+
+
 @click.command()
 @click.option('--debug', envvar='DEBUG', is_flag=True)
 @click.option('--port', envvar='PORT', default=8888)

requirements.txt

@@ -72,3 +72,6 @@ Flask-Alembic==2.0.1 \
     --hash=sha256:7e67740b0b08d58dcae0c701d56b56e60f5fa4af907bb82b4cb0469229ba94ff
 uWSGI==2.0.15 \
     --hash=sha256:572ef9696b97595b4f44f6198fe8c06e6f4e6351d930d22e5330b071391272ff
+mozlogging==0.1.0 \
+    --hash=sha256:2fc3d520a17b048c8723abdba19f6c01f2bcaf4182944aaac5906f28bd5b7d77 \
+    --hash=sha256:2e1362b80418b845164d8d47337da838dade05720dbaf17956d1cafebc511b94