Add private Prometheus API metrics and Grafana performance dashboard

backend/tests/test_metrics.py

@@ -0,0 +1,20 @@
+import unittest
+from types import SimpleNamespace
+from prometheus_client import REGISTRY, generate_latest
+from backend.app.metrics import record_api, record_remote
+
+
+class MetricsTests(unittest.TestCase):
+    def test_route_template_not_private_path(self):
+        request = SimpleNamespace(method='GET', scope={'route': SimpleNamespace(path='/requests/{request_id}')})
+        before = REGISTRY.get_sample_value('magent_api_requests_total', {'method': 'GET', 'route': '/requests/{request_id}', 'status': '200'}) or 0
+        record_api(request, 200, .1)
+        self.assertEqual(REGISTRY.get_sample_value('magent_api_requests_total', {'method': 'GET', 'route': '/requests/{request_id}', 'status': '200'}), before + 1)
+
+    def test_unknown_route_and_service_are_bounded(self):
+        record_api(SimpleNamespace(method='SECRET-USER-METHOD', scope={}), 404, .01)
+        record_remote('secret-service-name', 'GET', 'error', .1)
+        data = generate_latest().decode()
+        self.assertNotIn('secret-service-name', data)
+        self.assertNotIn('SECRET-USER-METHOD', data)
+        self.assertIn('route="unmatched"', data)