feat: move from gunicorn to waitress

Waitress, unlike unicorn, is multi-threaded. As it does not do access logs
by default, the app needs to be wrapped in TransLogger before being passed to
Waitress.

To make the switch, a custom registry is now also used instead of the global REGISTRY
as the default registry for the app. As part of this change, the default
prometheus metrics are then also registered with this new registry.

Closes: #72

app/__init__.py

@@ -7,7 +7,7 @@ from flask import Flask, redirect, url_for, send_from_directory
 from flask.typing import ResponseReturnValue
 from prometheus_client import make_wsgi_app, Metric, CollectorRegistry
 from prometheus_client.metrics_core import GaugeMetricFamily, CounterMetricFamily
-from prometheus_client.registry import Collector
+from prometheus_client.registry import Collector, REGISTRY
 from sqlalchemy import text
 from sqlalchemy.exc import SQLAlchemyError
 from werkzeug.middleware.dispatcher import DispatcherMiddleware
@@ -24,10 +24,18 @@ from app.tfstate import tfstate
 app = Flask(__name__)
 app.config.from_file("../config.yaml", load=yaml.safe_load)
 
+# create new registry to avoid multiple metrics registration in global REGISTRY
+registry = CollectorRegistry()
+
 app.wsgi_app = DispatcherMiddleware(app.wsgi_app, {  # type: ignore[method-assign]
-    '/metrics': make_wsgi_app()
+    '/metrics': make_wsgi_app(registry)
 })
 
+#register default collectors to our new registry
+collectors = list(REGISTRY._collector_to_names.keys())
+for collector in collectors:
+    registry.register(collector)
+
 db.init_app(app)
 migrate.init_app(app, db, render_as_batch=True)
 bootstrap.init_app(app)
@@ -129,9 +137,8 @@ class AutomationCollector(Collector):
                 ok.add_metric(["automation_state"], 0)
             yield ok
 
-
+# register all custom collectors to registry
 if not_migrating() and 'DISABLE_METRICS' not in os.environ:
-    registry = CollectorRegistry()
     registry.register(DefinedProxiesCollector())
     registry.register(BlockedProxiesCollector())
     registry.register(AutomationCollector())