feat: add healthcheck for metrics endpoint and improve latency observation

Author: milsman2

Dockerfile

@@ -24,3 +24,5 @@ USER nonroot
 WORKDIR /app/src
 EXPOSE 8000
 CMD ["python", "-m", "python_response_time.main"]
+HEALTHCHECK --interval=10s --timeout=3s --start-period=5s --retries=3 \
+  CMD python -c "import urllib.request; urllib.request.urlopen('http://127.0.0.1:8000/metrics').read()" || exit 1

src/python_response_time/main.py

@@ -86,7 +86,9 @@ def run_app():
                     }
                 )
                 REQUEST_COUNT.labels(status=str(response.status_code)).inc()
-                REQUEST_LATENCY.observe(elapsed)
+                REQUEST_LATENCY.labels(status=str(response.status_code)).observe(
+                    elapsed
+                )
             except requests.exceptions.SSLError as e:
                 console.print(f"{i + 1:>4} | SSL ERROR")
                 logger.error(