feat: simple prometheus asgi optional integration (experimental, will…

… change)

docs/operate/prometheus.rst

@@ -0,0 +1,30 @@
+Prometheus
+==========
+
+.. warning::
+
+    This feature is mostly for internal use for now, and although we'll keep a prometheus integration in the future,
+    configuration will change.
+
+Enable the middleware using ...
+
+.. code-block:: bash
+
+    USE_ASGI_PROMETHEUS_MIDDLEWARE=true harp ...
+
+Then you can access the metrics at ``/.prometheus/metrics``.
+
+Here is an example scrape configuration for prometheus:
+
+.. code-block:: yaml
+
+    scrape_configs:
+      - job_name: harp
+        honor_timestamps: true
+        scrape_interval: 10s
+        scrape_timeout: 10s
+        metrics_path: /.prometheus/metrics
+        scheme: http
+        static_configs:
+          - targets:
+              - url.or.ip.for.harp.example.com:4080

harp/config/adapters/hypercorn.py

@@ -5,6 +5,7 @@
 from hypercorn.utils import LifespanFailureError
 
 from harp import get_logger
+from harp.utils.env import get_bool_from_env
 
 logger = get_logger(__name__)
 
@@ -34,11 +35,19 @@ async def serve(self):
         from hypercorn.asyncio import serve
 
         asgi_app, binds = await self.factory.build()
+
+        if get_bool_from_env("USE_ASGI_PROMETHEUS_MIDDLEWARE", False):
+            from asgi_prometheus import PrometheusMiddleware
+
+            _metrics_url = "/.prometheus/metrics"
+            asgi_app = PrometheusMiddleware(asgi_app, metrics_url=_metrics_url, group_paths=["/"])
+            logger.info(f"🌎 PrometheusMiddleware enabled, metrics under {_metrics_url}.")
+
         config = self._create_config(binds)
         logger.debug(f"🌎 {type(self).__name__}::serve({', '.join(config.bind)})")
 
         try:
-            return await serve(asgi_app, config)
+            return await serve(asgi_app, config, mode="asgi")
         except LifespanFailureError as exc:
             logger.exception(f"Server initiliation failed: {repr(exc.__cause__)}", exc_info=exc.__cause__)
             if isinstance(exc.__cause__, PostgresError):

harp/utils/env.py

@@ -20,6 +20,6 @@ def get_bool_from_env(key, default):
         return default
 
     try:
-        return cast_bool(key)
+        return cast_bool(value)
     except ValueError:
         raise ValueError(f"Invalid boolean value for {key}: {value!r}")

harp/utils/tests/test_env.py

@@ -0,0 +1,28 @@
+from unittest.mock import patch
+
+import pytest
+
+from harp.utils.env import cast_bool, get_bool_from_env
+
+parametrize_with_string_booleans = pytest.mark.parametrize(
+    "value, expected",
+    [
+        ("true", True),
+        ("yes", True),
+        ("1", True),
+        ("false", False),
+        ("no", False),
+        ("0", False),
+    ],
+)
+
+
+@parametrize_with_string_booleans
+def test_cast_bool(value, expected):
+    assert cast_bool(value) == expected
+
+
+@parametrize_with_string_booleans
+def test_get_bool_from_env(value, expected):
+    with patch.dict("os.environ", {"TEST_ENV_VAR": value}):
+        assert get_bool_from_env("TEST_ENV_VAR", False) == expected

pyproject.toml

@@ -47,6 +47,7 @@ svix-ksuid = "^0.6.2"
 watchfiles = { version = "^0.22.0", optional = true }
 whistle = { version = "2.0.0b1", allow-prereleases = true }
 pyheck = "^0.1.5"
+asgi-prometheus = "^1.1.2"
 
 
 [tool.poetry.group.dev.dependencies]