Use Gunicorn for container server

Dockerfile

@@ -43,6 +43,7 @@ COPY schema_mssql.sql ./
 COPY app.py .
 COPY config.py .
 COPY dash_app.py .
+COPY gunicorn.conf.py .
 COPY assets/ ./assets/
 COPY static/ ./static/
 COPY pages/ ./pages/
@@ -59,9 +60,11 @@ RUN groupadd --gid 10001 app && \
 # Expose single internal app port; external ports are mapped via docker-compose
 EXPOSE 5000
 
-# Run the app
+# Run the app with a production-grade WSGI server. Gunicorn keeps a master
+# process alive to replace failed workers and does not run Flask's debug
+# reloader, so application workers cannot silently reload inside the container.
 USER app
-CMD ["python", "app.py"]
+CMD ["gunicorn", "--config", "gunicorn.conf.py", "app:server"]
 
 # Dev-only stage: add Microsoft ODBC Driver for SQL Server (local dev container)
 FROM base AS dev

gunicorn.conf.py

@@ -0,0 +1,30 @@
+"""Gunicorn configuration for the HapSearch container."""
+
+import os
+
+
+bind = f"{os.getenv('APP_HOST', '0.0.0.0')}:{os.getenv('APP_PORT', '5000')}"
+
+# Multiple threaded workers keep the site available when a request is slow or
+# a worker exits. Every value can be tuned per environment without rebuilding.
+workers = int(os.getenv("GUNICORN_WORKERS", "2"))
+worker_class = "gthread"
+threads = int(os.getenv("GUNICORN_THREADS", "4"))
+timeout = int(os.getenv("GUNICORN_TIMEOUT", "120"))
+graceful_timeout = int(os.getenv("GUNICORN_GRACEFUL_TIMEOUT", "30"))
+keepalive = int(os.getenv("GUNICORN_KEEPALIVE", "5"))
+
+# Periodically replace workers to limit the impact of gradual memory growth.
+# Jitter prevents all workers from being recycled at the same time.
+max_requests = int(os.getenv("GUNICORN_MAX_REQUESTS", "2000"))
+max_requests_jitter = int(os.getenv("GUNICORN_MAX_REQUESTS_JITTER", "200"))
+
+accesslog = "-"
+errorlog = "-"
+capture_output = True
+
+# The existing load balancer connects to this backend over HTTPS. Local
+# environments can disable TLS by leaving TLS_ENABLED unset or false.
+if os.getenv("TLS_ENABLED", "false").lower() in {"true", "1", "yes"}:
+    certfile = os.getenv("TLS_CERT_PATH", "/cert.pem")
+    keyfile = os.getenv("TLS_KEY_PATH", "/key.pem")