feat: run with gunicorn instead of flask

Each worker now uses its own registry instead of the global REGISTRY
to avoid duplicate metric registration, since metrics are served
from the database.

app/__init__.py

@@ -5,7 +5,7 @@ from typing import Iterator
 import yaml
 from flask import Flask, redirect, url_for, send_from_directory
 from flask.typing import ResponseReturnValue
-from prometheus_client import make_wsgi_app, REGISTRY, Metric
+from prometheus_client import make_wsgi_app, Metric, CollectorRegistry
 from prometheus_client.metrics_core import GaugeMetricFamily, CounterMetricFamily
 from prometheus_client.registry import Collector
 from sqlalchemy import text
@@ -106,9 +106,10 @@ class AutomationCollector(Collector):
 
 
 if not_migrating() and 'DISABLE_METRICS' not in os.environ:
-    REGISTRY.register(DefinedProxiesCollector())
-    REGISTRY.register(BlockedProxiesCollector())
-    REGISTRY.register(AutomationCollector())
+    registry = CollectorRegistry()
+    registry.register(DefinedProxiesCollector())
+    registry.register(BlockedProxiesCollector())
+    registry.register(AutomationCollector())
 
 
 @app.route('/ui')