Always use the the user configured logger class.

Previously, configuring statsd_host would override the configured class

docs/source/settings.rst

@@ -532,6 +532,10 @@ The logger you want to use to log events in Gunicorn.
 The default class (``gunicorn.glogging.Logger``) handle most of
 normal usages in logging. It provides error and access logging.
 
+If you enable statsd support, then a special subclass
+(``gunicorn.instrument.statsd.Statsd``) is used instead, which handles
+sending the metrics to *statsd_host*
+
 You can provide your own worker by giving Gunicorn a
 Python path to a subclass like ``gunicorn.glogging.Logger``.
 Alternatively the syntax can also load the Logger class
@@ -611,6 +615,9 @@ statsd_host
 
 ``host:port`` of the statsd server to log to.
 
+Note: enabling this switches the default *logger_class* to
+``gunicorn.instrument.statsd.Statsd``
+
 .. versionadded:: 19.1
 
 statsd_prefix

gunicorn/config.py

@@ -144,16 +144,18 @@ class Config(object):
         uri = self.settings['logger_class'].get()
         if uri == "simple":
             # support the default
-            uri = "gunicorn.glogging.Logger"
+            uri = LoggerClass.default
 
-        # if statsd is on, automagically switch to the statsd logger
-        if uri is not None and 'statsd_host' in self.settings and self.settings['statsd_host'].value is not None:
-            logger_class = util.load_class("gunicorn.instrument.statsd.Statsd",
-                section="gunicorn.loggers")
-        else:
-            logger_class = util.load_class(uri,
-                default="gunicorn.glogging.Logger",
-                section="gunicorn.loggers")
+        # if default logger is in use, and statsd is on, automagically switch
+        # to the statsd logger
+        if uri == LoggerClass.default:
+            if 'statsd_host' in self.settings and self.settings['statsd_host'].value is not None:
+                uri = "gunicorn.instrument.statsd.Statsd"
+
+        logger_class = util.load_class(
+            uri,
+            default="gunicorn.glogging.Logger",
+            section="gunicorn.loggers")
 
         if hasattr(logger_class, "install"):
             logger_class.install()

tests/test_config.py

@@ -13,6 +13,8 @@ import pytest
 from gunicorn import config
 from gunicorn.app.base import Application
 from gunicorn.workers.sync import SyncWorker
+from gunicorn import glogging
+from gunicorn.instrument import statsd
 
 dirname = os.path.dirname(__file__)
 def cfg_module():
@@ -57,6 +59,9 @@ def test_property_access():
     # Class was loaded
     assert c.worker_class == SyncWorker
 
+    # logger class was loaded
+    assert c.logger_class == glogging.Logger
+
     # Workers defaults to 1
     assert c.workers == 1
     c.set("workers", 3)
@@ -259,3 +264,24 @@ def test_nworkers_changed():
 
     c.set("nworkers_changed", nworkers_changed_3)
     assert c.nworkers_changed(1, 2, 3) == 3
+
+
+def test_statsd_changes_logger():
+    c = config.Config()
+    assert c.logger_class == glogging.Logger
+    c.set('statsd_host', 'localhost:12345')
+    assert c.logger_class == statsd.Statsd
+
+
+class MyLogger(glogging.Logger):
+    # dummy custom logger class for testing
+    pass
+
+
+def test_always_use_configured_logger():
+    c = config.Config()
+    c.set('logger_class', __name__ + '.MyLogger')
+    assert c.logger_class == MyLogger
+    c.set('statsd_host', 'localhost:12345')
+    # still uses custom logger over statsd
+    assert c.logger_class == MyLogger