metering: add middleware for HTTP metrics

src/schema_registry/__main__.py

@@ -21,6 +21,7 @@
 import schema_registry.routers.mode
 import schema_registry.routers.schemas
 import schema_registry.routers.subjects
+import schema_registry.telemetry.meter
 import schema_registry.telemetry.middleware
 import schema_registry.telemetry.setup
 import schema_registry.telemetry.tracer
@@ -34,6 +35,7 @@
             __name__,
             schema_registry.controller,
             schema_registry.telemetry.tracer,
+            schema_registry.telemetry.meter,
         ]
     )
 

src/schema_registry/factory.py

@@ -17,7 +17,7 @@
 from schema_registry.middlewares import setup_middlewares
 from schema_registry.registry import KarapaceSchemaRegistry
 from schema_registry.routers.setup import setup_routers
-from schema_registry.telemetry.setup import setup_tracing
+from schema_registry.telemetry.setup import setup_metering, setup_tracing
 from typing import AsyncContextManager
 
 import logging
@@ -59,6 +59,7 @@ def create_karapace_application(
     app = FastAPI(lifespan=lifespan)  # type: ignore[arg-type]
 
     setup_tracing()
+    setup_metering()
     setup_routers(app=app)
     setup_exception_handlers(app=app)
     setup_middlewares(app=app)

src/schema_registry/telemetry/container.py

@@ -9,10 +9,11 @@
 from opentelemetry.sdk.resources import Resource
 from opentelemetry.sdk.trace import TracerProvider
 from opentelemetry.semconv.attributes import telemetry_attributes as T
+from schema_registry.telemetry.meter import Meter
 from schema_registry.telemetry.tracer import Tracer
 
 
-def create_tracing_resource(config: Config) -> Resource:
+def create_telemetry_resource(config: Config) -> Resource:
     return Resource.create(
         {
             "service.name": config.telemetry.resource_service_name,
@@ -26,6 +27,9 @@ def create_tracing_resource(config: Config) -> Resource:
 
 class TelemetryContainer(containers.DeclarativeContainer):
     karapace_container = providers.Container(KarapaceContainer)
-    tracing_resource = providers.Factory(create_tracing_resource, config=karapace_container.config)
-    tracer_provider = providers.Singleton(TracerProvider, resource=tracing_resource)
+
+    telemetry_resource = providers.Factory(create_telemetry_resource, config=karapace_container.config)
+
+    meter = providers.Singleton(Meter)
     tracer = providers.Singleton(Tracer)
+    tracer_provider = providers.Singleton(TracerProvider, resource=telemetry_resource)

src/schema_registry/telemetry/middleware.py

@@ -6,11 +6,14 @@
 from collections.abc import Awaitable, Callable
 from dependency_injector.wiring import inject, Provide
 from fastapi import FastAPI, Request, Response
+from opentelemetry.metrics import Counter, Histogram, UpDownCounter
 from opentelemetry.trace import SpanKind
 from schema_registry.telemetry.container import TelemetryContainer
+from schema_registry.telemetry.meter import Meter
 from schema_registry.telemetry.tracer import Tracer
 
 import logging
+import time
 
 LOG = logging.getLogger(__name__)
 
@@ -20,12 +23,59 @@ async def telemetry_middleware(
     request: Request,
     call_next: Callable[[Request], Awaitable[Response]],
     tracer: Tracer = Provide[TelemetryContainer.tracer],
+    meter: Meter = Provide[TelemetryContainer.meter],
 ) -> Response:
     resource = request.url.path.split("/")[1]
     with tracer.get_tracer().start_as_current_span(name=f"{request.method}: /{resource}", kind=SpanKind.SERVER) as span:
+        span.add_event("Creating metering resources")
+        karapace_http_requests_in_progress: UpDownCounter = meter.get_meter().create_up_down_counter(
+            name="karapace_http_requests_in_progress",
+            description="In-progress requests for HTTP/TCP Protocol",
+        )
+        karapace_http_requests_duration_seconds: Histogram = meter.get_meter().create_histogram(
+            unit="seconds",
+            name="karapace_http_requests_duration_seconds",
+            description="Request Duration for HTTP/TCP Protocol",
+        )
+        karapace_http_requests_total: Counter = meter.get_meter().create_counter(
+            name="karapace_http_requests_total",
+            description="Total Request Count for HTTP/TCP Protocol",
+        )
+
+        # Set start time for request
+        setattr(request.state, meter.START_TIME_KEY, time.monotonic())
+
+        # Extract request labels
+        path = request.url.path
+        method = request.method
+
+        # Increment requests in progress before response handler
+        span.add_event("Metering requests in progress (increase)")
+        karapace_http_requests_in_progress.add(amount=1, attributes={"method": method, "path": path})
+
+        # Call request handler
         tracer.update_span_with_request(request=request, span=span)
+        span.add_event("Calling request handler")
         response: Response = await call_next(request)
         tracer.update_span_with_response(response=response, span=span)
+
+        # Instrument request duration
+        span.add_event("Metering request duration")
+        karapace_http_requests_duration_seconds.record(
+            amount=(time.monotonic() - getattr(request.state, meter.START_TIME_KEY)),
+            attributes={"method": method, "path": path},
+        )
+
+        # Instrument total requests
+        span.add_event("Metering total requests")
+        karapace_http_requests_total.add(
+            amount=1, attributes={"method": method, "path": path, "status": response.status_code}
+        )
+
+        # Decrement requests in progress after response handler
+        span.add_event("Metering requests in progress (decrease)")
+        karapace_http_requests_in_progress.add(amount=-1, attributes={"method": method, "path": path})
+
         return response
 
 

src/schema_registry/telemetry/setup.py

@@ -4,9 +4,12 @@
 """
 
 from dependency_injector.wiring import inject, Provide
-from opentelemetry import trace
+from opentelemetry import metrics, trace
+from opentelemetry.sdk.metrics import MeterProvider
+from opentelemetry.sdk.resources import Resource
 from opentelemetry.sdk.trace import TracerProvider
 from schema_registry.telemetry.container import TelemetryContainer
+from schema_registry.telemetry.meter import Meter
 from schema_registry.telemetry.tracer import Tracer
 
 import logging
@@ -22,3 +25,12 @@ def setup_tracing(
     LOG.info("Setting OTel tracing provider")
     tracer_provider.add_span_processor(tracer.get_span_processor())
     trace.set_tracer_provider(tracer_provider)
+
+
+@inject
+def setup_metering(
+    meter: Meter = Provide[TelemetryContainer.meter],
+    telemetry_resource: Resource = Provide[TelemetryContainer.telemetry_resource],
+) -> None:
+    LOG.info("Setting OTel meter provider")
+    metrics.set_meter_provider(MeterProvider(resource=telemetry_resource, metric_readers=[meter.get_metric_reader()]))

tests/unit/schema_registry/telemetry/test_middleware.py

@@ -8,9 +8,10 @@
 from _pytest.logging import LogCaptureFixture
 from fastapi import FastAPI, Request, Response
 from opentelemetry.trace import SpanKind
+from schema_registry.telemetry.meter import Meter
 from schema_registry.telemetry.middleware import setup_telemetry_middleware, telemetry_middleware
 from schema_registry.telemetry.tracer import Tracer
-from unittest.mock import AsyncMock, MagicMock
+from unittest.mock import AsyncMock, call, MagicMock, patch
 
 import logging
 
@@ -31,26 +32,64 @@ def test_setup_telemetry_middleware(caplog: LogCaptureFixture) -> None:
 
 async def test_telemetry_middleware() -> None:
     tracer = MagicMock(spec=Tracer)
+    meter = MagicMock(spec=Meter, START_TIME_KEY="start_time")
 
     request_mock = AsyncMock(spec=Request)
     request_mock.method = "GET"
-    request_mock.url.path = "/test"
+    request_mock.url.path = "/test/inner-path"
 
     response_mock = AsyncMock(spec=Response)
     response_mock.status_code = 200
 
     call_next = AsyncMock()
     call_next.return_value = response_mock
 
-    response = await telemetry_middleware(request=request_mock, call_next=call_next, tracer=tracer)
-    span = tracer.get_tracer.return_value.start_as_current_span.return_value.__enter__.return_value
-
-    tracer.get_tracer.assert_called_once()
-    tracer.get_tracer.return_value.start_as_current_span.assert_called_once_with(name="GET: /test", kind=SpanKind.SERVER)
-    tracer.update_span_with_request.assert_called_once_with(request=request_mock, span=span)
-    tracer.update_span_with_response.assert_called_once_with(response=response_mock, span=span)
-
-    # Check that the request handler is called
-    call_next.assert_awaited_once_with(request_mock)
-
-    assert response == response_mock
+    with patch("schema_registry.telemetry.middleware.time.monotonic", return_value=1):
+        response = await telemetry_middleware(request=request_mock, call_next=call_next, tracer=tracer, meter=meter)
+        span = tracer.get_tracer.return_value.start_as_current_span.return_value.__enter__.return_value
+
+        tracer.get_tracer.assert_called_once()
+        tracer.get_tracer.return_value.start_as_current_span.assert_called_once_with(name="GET: /test", kind=SpanKind.SERVER)
+        tracer.update_span_with_request.assert_called_once_with(request=request_mock, span=span)
+        tracer.update_span_with_response.assert_called_once_with(response=response_mock, span=span)
+
+        # Check that the request handler is called
+        call_next.assert_awaited_once_with(request_mock)
+
+        span.add_event.assert_has_calls(
+            [
+                call("Creating metering resources"),
+                call("Metering requests in progress (increase)"),
+                call("Calling request handler"),
+                call("Metering request duration"),
+                call("Metering total requests"),
+                call("Metering requests in progress (decrease)"),
+            ]
+        )
+
+        meter.get_meter.assert_has_calls(
+            [
+                call(),
+                call().create_up_down_counter(
+                    name="karapace_http_requests_in_progress", description="In-progress requests for HTTP/TCP Protocol"
+                ),
+                call(),
+                call().create_histogram(
+                    unit="seconds",
+                    name="karapace_http_requests_duration_seconds",
+                    description="Request Duration for HTTP/TCP Protocol",
+                ),
+                call(),
+                call().create_counter(
+                    name="karapace_http_requests_total", description="Total Request Count for HTTP/TCP Protocol"
+                ),
+                call().create_up_down_counter().add(amount=1, attributes={"method": "GET", "path": "/test/inner-path"}),
+                call().create_histogram().record(amount=0, attributes={"method": "GET", "path": "/test/inner-path"}),
+                call()
+                .create_counter()
+                .add(amount=1, attributes={"method": "GET", "path": "/test/inner-path", "status": 200}),
+                call().create_up_down_counter().add(amount=-1, attributes={"method": "GET", "path": "/test/inner-path"}),
+            ]
+        )
+
+        assert response == response_mock