Don't expose metrics on production port (openlabs#14)

* /metrics endpoint is now exposed via port 9191 only. This closes openlabs#13.
* Remove some duplicate code in case of /metrics request.
* Reorder if clause to match as early as possible.

Dockerfile

@@ -9,8 +9,8 @@ RUN apt-get update && \
     rm -rf /var/lib/apt/lists/* /var/tmp/* /tmp/*
 
 ADD src/* /
-EXPOSE 5555
+EXPOSE 5555 9191
 
 ENTRYPOINT ["usr/local/bin/gunicorn"]
 
-CMD ["-b", "0.0.0.0:5555", "--log-file", "-", "app:application"]
+CMD ["-b", "0.0.0.0:5555", "-b", "0.0.0.0:9191", "--log-file", "-", "app:application"]

src/app.py

@@ -17,9 +17,8 @@
 from prometheus import prometheus_metrics
 
 @Request.application
-@prometheus_metrics('/metrics', ('/', '/healthz'))
+@prometheus_metrics(9191, '/metrics', ('/', '/healthz'))
 def application(request):
-
     if request.method == 'GET':
         return Response(status=status.OK)
 

src/prometheus.py

@@ -14,7 +14,7 @@
     ['method', 'endpoint', 'code']
 )
 
-def prometheus_metrics(metrics_path, monitor_endpoints):
+def prometheus_metrics(metrics_port, metrics_path, monitor_endpoints):
     monitor_endpoints = set([metrics_path] + list(monitor_endpoints))
     def prometheus_metrics_decorator(f):
         @wraps(f)
@@ -25,17 +25,15 @@ def f_wrapper(request):
                 return f(request)
 
             start_time = time()
-            if request.method == 'GET' and request.path == metrics_path:
-                status = 200
-                REQUEST_LATENCIES.labels(
-                    request.method, request.path, status
-                ).observe(time() - start_time)
-
-                REQUEST_COUNT.labels(request.method, request.path, status).inc()
-                return Response(generate_latest(REGISTRY), status=status)
-
-            with REQUEST_COUNT.labels(request.method, request.path, 500).count_exceptions():
-                response = f(request)
+            # Only respond to /metrics requests via dedicated metrics port
+            request_port = int(request.environ.get('SERVER_PORT', '-1'))
+            if request_port == metrics_port and \
+                    request.path == metrics_path and \
+                    request.method == 'GET':
+                response = Response(generate_latest(REGISTRY), status=200)
+            else:
+                with REQUEST_COUNT.labels(request.method, request.path, 500).count_exceptions():
+                    response = f(request)
 
             REQUEST_COUNT.labels(
                 request.method,