Registry a no-op metrics service by default

kinto/core/initialization.py

@@ -431,6 +431,9 @@ def on_new_response(event):
 def setup_metrics(config):
     settings = config.get_settings()
 
+    # Register a no-op metrics service by default.
+    config.registry.registerUtility(metrics.NoOpMetricsService(), metrics.IMetricsService)
+
     # This does not fully respect the Pyramid/ZCA patterns, but the rest of Kinto uses
     # `registry.storage`, `registry.cache`, etc. Consistency seems more important.
     config.registry.__class__.metrics = property(
@@ -449,9 +452,6 @@ def deprecated_registry(self):
     def on_app_created(event):
         config = event.app
         metrics_service = config.registry.metrics
-        if not metrics_service:
-            logger.warning("No metrics service registered.")
-            return
 
         metrics.watch_execution_time(metrics_service, config.registry.cache, prefix="backend")
         metrics.watch_execution_time(metrics_service, config.registry.storage, prefix="backend")
@@ -471,8 +471,6 @@ def on_app_created(event):
     def on_new_response(event):
         request = event.request
         metrics_service = config.registry.metrics
-        if not metrics_service:
-            return
 
         # Count unique users.
         user_id = request.prefixed_userid

kinto/core/metrics.py

@@ -1,6 +1,6 @@
 import types
 
-from zope.interface import Interface
+from zope.interface import Interface, implementer
 
 from kinto.core import utils
 
@@ -23,6 +23,30 @@ def count(key, count=1, unique=None):
         """
 
 
+class NoOpTimer:
+    def __call__(self, f):
+        @utils.safe_wraps(f)
+        def _wrapped(*args, **kwargs):
+            return f(*args, **kwargs)
+
+        return _wrapped
+
+    def __enter__(self):
+        pass
+
+    def __exit__(self, *args, **kwargs):
+        pass
+
+
+@implementer(IMetricsService)
+class NoOpMetricsService:
+    def timer(self, key):
+        return NoOpTimer()
+
+    def count(self, key, count=1, unique=None):
+        pass
+
+
 def watch_execution_time(metrics_service, obj, prefix="", classname=None):
     """
     Decorate all methods of an object in order to watch their execution time.
@@ -49,6 +73,8 @@ def listener_with_timer(config, key, func):
     def wrapped(*args, **kwargs):
         metrics_service = config.registry.metrics
         if not metrics_service:
+            # This only happens if `kinto.core.initialization.setup_metrics` is
+            # not listed in the `initialization_sequence` setting.
             return func(*args, **kwargs)
         # If metrics are enabled, monitor execution time of listeners.
         with metrics_service.timer(key):

kinto/core/utils.py

@@ -1,4 +1,5 @@
 import collections.abc as collections_abc
+import functools
 import hashlib
 import hmac
 import os
@@ -541,3 +542,10 @@ def apply_json_patch(obj, ops):
         raise ValueError(e)
 
     return result
+
+
+def safe_wraps(wrapper, *args, **kwargs):
+    """Safely wraps partial functions."""
+    while isinstance(wrapper, functools.partial):
+        wrapper = wrapper.func
+    return functools.wraps(wrapper, *args, **kwargs)

kinto/plugins/prometheus.py

@@ -1,11 +1,11 @@
-import functools
 from time import perf_counter as time_now
 
 from pyramid.exceptions import ConfigurationError
 from pyramid.response import Response
 from zope.interface import implementer
 
 from kinto.core import metrics
+from kinto.core.utils import safe_wraps
 
 
 try:
@@ -30,13 +30,6 @@ def _fix_metric_name(s):
     return s.replace("-", "_").replace(".", "_")
 
 
-def safe_wraps(wrapper, *args, **kwargs):
-    """Safely wraps partial functions."""
-    while isinstance(wrapper, functools.partial):
-        wrapper = wrapper.func
-    return functools.wraps(wrapper, *args, **kwargs)
-
-
 class Timer:
     def __init__(self, summary):
         self.summary = summary