refactor: decouple Prometheus metrics endpoint into a separate server

Author: MickaelCa

.pre-commit-config.yaml

@@ -117,6 +117,7 @@ repos:
             'fastapi[standard]>=0.109.1',
             httpx,
             pathspec>=0.12.1,
+            prometheus-client,
             pydantic,
             pytest-asyncio,
             pytest-mock,
@@ -138,6 +139,7 @@ repos:
             'fastapi[standard]>=0.109.1',
             httpx,
             pathspec>=0.12.1,
+            prometheus-client,
             pydantic,
             pytest-asyncio,
             pytest-mock,

Dockerfile

@@ -43,4 +43,5 @@ RUN set -eux; \
 USER appuser
 
 EXPOSE 8000
+EXPOSE 9090
 CMD ["python", "-m", "uvicorn", "server.main:app", "--host", "0.0.0.0", "--port", "8000"]

requirements.txt

@@ -2,10 +2,10 @@ click>=8.0.0
 fastapi[standard]>=0.109.1  # Vulnerable to https://osv.dev/vulnerability/PYSEC-2024-38
 httpx
 pathspec>=0.12.1
+prometheus-client
 pydantic
 python-dotenv
 slowapi
 starlette>=0.40.0  # Vulnerable to https://osv.dev/vulnerability/GHSA-f96h-pmfr-66vw
 tiktoken>=0.7.0  # Support for o200k_base encoding
 uvicorn>=0.11.7  # Vulnerable to https://osv.dev/vulnerability/PYSEC-2020-150
-prometheus-client

src/server/main.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import os
+import threading
 from pathlib import Path
 
 from dotenv import load_dotenv
@@ -12,7 +13,8 @@
 from slowapi.errors import RateLimitExceeded
 from starlette.middleware.trustedhost import TrustedHostMiddleware
 
-from server.routers import dynamic, index, ingest, metrics
+from server.metrics_server import start_metrics_server
+from server.routers import dynamic, index, ingest
 from server.server_config import templates
 from server.server_utils import lifespan, limiter, rate_limit_exception_handler
 
@@ -26,6 +28,17 @@
 # Register the custom exception handler for rate limits
 app.add_exception_handler(RateLimitExceeded, rate_limit_exception_handler)
 
+# Start metrics server in a separate thread if enabled
+if os.getenv("GITINGEST_METRICS_ENABLED", "false").lower() == "true":
+    metrics_host = os.getenv("GITINGEST_METRICS_HOST", "127.0.0.1")
+    metrics_port = int(os.getenv("GITINGEST_METRICS_PORT", "9090"))
+    metrics_thread = threading.Thread(
+        target=start_metrics_server,
+        args=(metrics_host, metrics_port),
+        daemon=True,
+    )
+    metrics_thread.start()
+
 
 # Mount static files dynamically to serve CSS, JS, and other static assets
 static_dir = Path(__file__).parent.parent / "static"
@@ -159,8 +172,6 @@ def openapi_json() -> JSONResponse:
 
 
 # Include routers for modular endpoints
-if os.getenv("GITINGEST_PROMETHEUS_TOKEN") is not None:
-    app.include_router(metrics)
 app.include_router(index)
 app.include_router(ingest)
 app.include_router(dynamic)

src/server/metrics_server.py

@@ -0,0 +1,57 @@
+"""Prometheus metrics server running on a separate port."""
+
+import logging
+
+import uvicorn
+from fastapi import FastAPI
+from fastapi.responses import HTMLResponse
+from prometheus_client import REGISTRY, generate_latest
+
+# Create a logger for this module
+logger = logging.getLogger(__name__)
+
+# Create a separate FastAPI app for metrics
+metrics_app = FastAPI(
+    title="Gitingest Metrics",
+    description="Prometheus metrics for Gitingest",
+    docs_url=None,
+    redoc_url=None,
+)
+
+
+@metrics_app.get("/metrics")
+async def metrics() -> HTMLResponse:
+    """Serve Prometheus metrics without authentication.
+
+    This endpoint is only accessible from the local network.
+
+    Returns
+    -------
+    HTMLResponse
+        Prometheus metrics in text format
+
+    """
+    return HTMLResponse(
+        content=generate_latest(REGISTRY),
+        status_code=200,
+        media_type="text/plain",
+    )
+
+
+def start_metrics_server(host: str = "127.0.0.1", port: int = 9090) -> None:
+    """Start the metrics server on a separate port.
+
+    Parameters
+    ----------
+    host : str
+        The host to bind to (default: 127.0.0.1 for local network only)
+    port : int
+        The port to bind to (default: 9090)
+
+    Returns
+    -------
+    None
+
+    """
+    logger.info("Starting metrics server on %s:%s", host, port)
+    uvicorn.run(metrics_app, host=host, port=port)

src/server/routers/__init__.py

@@ -3,6 +3,5 @@
 from server.routers.dynamic import router as dynamic
 from server.routers.index import router as index
 from server.routers.ingest import router as ingest
-from server.routers.metrics import router as metrics
 
-__all__ = ["dynamic", "index", "ingest", "metrics"]
+__all__ = ["dynamic", "index", "ingest"]

src/server/routers/metrics.py

@@ -2,6 +2,8 @@
 
 from __future__ import annotations
 
+from pathlib import Path
+
 from fastapi.templating import Jinja2Templates
 
 MAX_DISPLAY_SIZE: int = 300_000
@@ -19,4 +21,7 @@
     {"name": "ApiAnalytics", "url": "https://github.com/tom-draper/api-analytics"},
 ]
 
-templates = Jinja2Templates(directory="server/templates")
+
+# Use absolute path to templates directory
+templates_dir = Path(__file__).parent / "templates"
+templates = Jinja2Templates(directory=templates_dir)