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

Dockerfile

@@ -4,15 +4,15 @@ ENV APP="bc"
 ENV APP_BASE="/srv"
 ENV SHELL="/bin/bash"
 ENV FLASK_APP="${FLASK_APP:-app}"
-ENV GUNICORN_RUN_HOST="${GUNICORN_RUN_HOST:-0.0.0.0}"
-ENV GUNICORN_RUN_PORT="${GUNICORN_RUN_PORT:-5000}"
+ENV WAITRESS_RUN_HOST="${WAITRESS_RUN_HOST:-0.0.0.0}"
+ENV WAITRESS_RUN_PORT="${WAITRESS_RUN_PORT:-5000}"
 ENV PYTHONPATH="${APP_BASE}/env/lib/python3.11/site-packages"
 ENV PATH="${APP_BASE}/env/bin:/usr/local/bin:/usr/bin:/bin:/sbin:/usr/sbin:/home/${APP}/.local/bin"
 
 ARG CONTAINER_UID="${CONTAINER_UID:-1000}"
 ARG CONTAINER_GID="${CONTAINER_GID:-1000}"
 
-ENV GUNICORN_WORKERS="${GUNICORN_WORKERS:-4}"
+ENV WAITRESS_THREADS="${WAITRESS_THREADS:-4}"
 
 RUN apt-get update && \
     apt-get install --no-install-recommends -y \
@@ -49,11 +49,9 @@ USER ${APP}
 
 WORKDIR ${APP_BASE}/${APP}
 COPY --chown=${APP}:${APP} . ${APP_BASE}/${APP}
-RUN chmod +x ${APP_BASE}/${APP}/run_gunicorn.sh
 
 RUN python3 -m venv ${APP_BASE}/env && \
     ${APP_BASE}/env/bin/pip install --no-cache-dir -r requirements.txt && \
-    ${APP_BASE}/env/bin/pip install --no-cache-dir psycopg2-binary gunicorn
-
+    ${APP_BASE}/env/bin/pip install --no-cache-dir psycopg2-binary waitress paste
 RUN make install-frontend
-ENTRYPOINT ["./run_gunicorn.sh"]
+ENTRYPOINT ["python", "./run_waitress.py"]

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())

run_gunicorn.sh

@@ -1,4 +0,0 @@
-#!/bin/sh
-
-flask db upgrade
-gunicorn "$FLASK_APP".__init__:app -w "$GUNICORN_WORKERS" --access-logfile=- -b "$GUNICORN_RUN_HOST:$GUNICORN_RUN_PORT"

run_waitress.py

@@ -0,0 +1,11 @@
+import os
+from waitress import serve
+from paste.translogger import TransLogger
+from app.__init__ import app
+from flask_migrate import upgrade
+
+# equivalent of running flask db upgrade
+with app.app_context():
+    upgrade()
+
+serve(TransLogger(app), host=os.environ["WAITRESS_RUN_HOST"], port=os.environ["WAITRESS_RUN_PORT"], threads=int(os.environ["WAITRESS_THREADS"]))