Require prefix unless allow_no_prefix is set.

sprockets_statsd/mixins.py

@@ -25,7 +25,7 @@ class Application(web.Application):
     +-------------------+---------------------------------------------+
     | port              | port number that statsd is listening on     |
     +-------------------+---------------------------------------------+
-    | prefix            | segment to prefix to metrics.               |
+    | prefix            | segment to prefix to metrics                |
     +-------------------+---------------------------------------------+
     | protocol          | "tcp" or "udp"                              |
     +-------------------+---------------------------------------------+
@@ -47,12 +47,18 @@ class Application(web.Application):
 
     **prefix** is prefixed to all metric paths.  This provides a
     namespace for metrics so that each applications metrics are maintained
-    in separate buckets.
+    in separate buckets.  The default is to use the :envvar:`STATSD_PREFIX`
+    environment variable.  If it is unset and the *service* and
+    *environment* keys are set in ``settings``, then the default is
+    ``applications.<service>.<environment>``.  This is a convenient way to
+    maintain consistent metric paths when you are managing a larger number
+    of services.
 
-    If the *service* and *environment* keys are set in ``settings``,
-    then the default prefix is ``applications.<service>.<environment>``.
-    This is a convenient way to maintain consistent metric paths when
-    you are managing a larger number of services.
+    .. rubric:: Warning
+
+    If you want to run without a prefix, then you are required to also
+    set the ``allow_no_prefix`` key with a *truthy* value.  This prevents
+    accidentilly polluting the metric namespace with unqualified paths.
 
     **protocol** defaults to the :envvar:`STATSD_PROTOCOL` environment
     variable with a back default of "tcp" if the environment variable
@@ -102,6 +108,11 @@ class Application(web.Application):
         """
         if self.statsd_connector is None:
             statsd_settings = self.settings['statsd']
+            if (statsd_settings.get('prefix', None) is None
+                    and not statsd_settings.get('allow_no_prefix', False)):
+                raise RuntimeError(
+                    'statsd configuration error: prefix is not set')
+
             kwargs = {
                 'host': statsd_settings['host'],
                 'port': statsd_settings['port'],

tests/test_mixins.py

@@ -115,10 +115,51 @@ class ApplicationTests(AsyncTestCaseWithTimeout):
         with self.assertRaises(RuntimeError):
             self.run_coroutine(app.start_statsd())
 
+    def test_that_starting_without_prefix_fails_by_default(self):
+        self.unsetenv('STATSD_PREFIX')
+        app = sprockets_statsd.mixins.Application(statsd={
+            'host': 'statsd.example.com',
+            'protocol': 'udp',
+        })
+        with self.assertRaises(RuntimeError) as cm:
+            self.run_coroutine(app.start_statsd())
+        self.assertTrue('prefix is not set' in str(cm.exception),
+                        'Expected "prefix is not set" in exception message')
+
+    def test_starting_without_prefix_on_purpose(self):
+        self.unsetenv('STATSD_PREFIX')
+        app = sprockets_statsd.mixins.Application(
+            statsd={
+                'allow_no_prefix': True,
+                'host': 'statsd.example.com',
+                'protocol': 'udp',
+            })
+        try:
+            self.run_coroutine(app.start_statsd())
+        finally:
+            self.run_coroutine(app.stop_statsd())
+
+    def test_starting_with_calculated_prefix(self):
+        self.unsetenv('STATSD_PREFIX')
+        app = sprockets_statsd.mixins.Application(
+            environment='development',
+            service='my-service',
+            statsd={
+                'host': 'statsd.example.com',
+                'protocol': 'udp',
+            })
+        try:
+            self.run_coroutine(app.start_statsd())
+            self.assertEqual('applications.my-service.development',
+                             app.settings['statsd']['prefix'])
+        finally:
+            self.run_coroutine(app.stop_statsd())
+
     def test_starting_twice(self):
         app = sprockets_statsd.mixins.Application(statsd={
             'host': 'localhost',
             'port': '8125',
+            'prefix': 'my-service',
         })
         try:
             self.run_coroutine(app.start_statsd())
@@ -143,6 +184,7 @@ class ApplicationTests(AsyncTestCaseWithTimeout):
             statsd={
                 'host': 'localhost',
                 'port': '8125',
+                'prefix': 'my-service',
                 'reconnect_sleep': 0.5,
                 'wait_timeout': 0.25,
             })
@@ -156,6 +198,7 @@ class ApplicationTests(AsyncTestCaseWithTimeout):
     def test_starting_with_invalid_protocol(self):
         app = sprockets_statsd.mixins.Application(statsd={
             'host': 'localhost',
+            'prefix': 'my-service',
             'protocol': 'unknown'
         })
         with self.assertRaises(RuntimeError):
@@ -164,6 +207,7 @@ class ApplicationTests(AsyncTestCaseWithTimeout):
     def test_that_protocol_strings_are_translated(self):
         app = sprockets_statsd.mixins.Application(statsd={
             'host': 'localhost',
+            'prefix': 'my-service',
             'protocol': 'tcp',
         })
         self.run_coroutine(app.start_statsd())
@@ -173,6 +217,7 @@ class ApplicationTests(AsyncTestCaseWithTimeout):
 
         app = sprockets_statsd.mixins.Application(statsd={
             'host': 'localhost',
+            'prefix': 'my-service',
             'protocol': 'udp',
         })
         self.run_coroutine(app.start_statsd())