added prometheus metrics exporter

docker/Dockerfile

@@ -67,6 +67,7 @@ RUN --mount=type=cache,target=/pip-cache \
     -r requirements/memcached.txt \
     -r requirements/rsvg.txt \
     -r requirements/sentry.txt \
+    -r requirements/metrics.txt \
     -r requirements/server-asgi.txt && \
     pip install --cache-dir /pip-cache uwsgi
 

src/c3nav/mapdata/apps.py

@@ -7,3 +7,4 @@ class MapdataConfig(AppConfig):
     def ready(self):
         from c3nav.mapdata.utils.cache.changes import register_signals
         register_signals()
+        import c3nav.mapdata.metrics  # noqa

src/c3nav/mapdata/metrics.py

@@ -0,0 +1,30 @@
+from django.conf import settings
+from django.contrib.auth import get_user_model
+from django.core.cache import cache
+
+from c3nav.mapdata.models.report import Report
+
+if settings.METRCIS:
+    from prometheus_client import Gauge
+    from prometheus_client.core import REGISTRY, CounterMetricFamily
+    from prometheus_client.registry import Collector
+
+    users_total = Gauge('c3nav_users_total', 'Total number of users')
+    users_total.set_function(lambda: get_user_model().objects.count())
+    reports_total = Gauge('c3nav_reports_total', 'Total number of reports')
+    reports_total.set_function(lambda: Report.objects.count())
+    reports_open = Gauge('c3nav_reports_open', 'Number of open reports')
+    reports_open.set_function(lambda: Report.objects.filter(open=True).count()),
+
+    class APIStatsCollector(Collector):
+        def collect(self):
+            if settings.CACHES['default']['BACKEND'] == 'django.core.cache.backends.redis.RedisCache':
+                client = cache._cache.get_client()
+                for key in client.keys(f"*{settings.CACHES['default'].get('KEY_PREFIX', '')}apistats__*"):
+                    key = key.decode('utf-8').split(':', 2)[2]
+                    yield CounterMetricFamily(f'c3nav_{key}', key, value=cache.get(key))
+
+        def describe(self):
+            return list()
+
+    REGISTRY.register(APIStatsCollector())

src/c3nav/settings.py

@@ -7,7 +7,6 @@ from contextlib import suppress
 from pathlib import Path
 from typing import Optional
 
-import sass
 from django.contrib.messages import constants as messages
 from django.core.exceptions import ImproperlyConfigured
 from django.utils.crypto import get_random_string
@@ -394,6 +393,19 @@ with suppress(ImportError):
     import django_extensions  # noqa
     INSTALLED_APPS.append('django_extensions')
 
+METRCIS = config.getboolean('c3nav', 'metrics', fallback=False)
+if METRCIS:
+    try:
+        import django_prometheus  # noqa
+        INSTALLED_APPS.append('django_prometheus')
+        MIDDLEWARE = [
+            'django_prometheus.middleware.PrometheusBeforeMiddleware',
+            *MIDDLEWARE,
+            'django_prometheus.middleware.PrometheusAfterMiddleware',
+        ]
+    except ImportError:
+        METRCIS = False
+
 # Security settings
 X_FRAME_OPTIONS = 'DENY'
 

src/c3nav/urls.py

@@ -47,3 +47,8 @@ if settings.SERVE_ANYTHING:
         with suppress(ImportError):
             import debug_toolbar
             urlpatterns.insert(0, path('__debug__/', include(debug_toolbar.urls)))
+
+    if settings.METRCIS:
+        with suppress(ImportError):
+            import django_prometheus  # noqu
+            urlpatterns.insert(0, path('prometheus/', include('django_prometheus.urls')))

src/requirements/metrics.txt

@@ -0,0 +1 @@
+django_prometheus==2.3.1