Failling to run a waitress (flask) webserver with NGINX

I have been trying to run a flask waitress server on ubuntu with NGINX.

This is my current NGINX config:

server {    listen 80;    server_name mydomain.com www.mydomain.com;    client_max_body_size 64M;  # Adjust the size as needed    large_client_header_buffers 4 32k;    location / {        proxy_pass http://127.0.0.1:80;        proxy_set_header Host $host;        proxy_set_header X-Real-IP $remote_addr;        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;        proxy_set_header X-Forwarded-Proto $scheme;    }    listen 443 ssl; # managed by Certbot    ssl_certificate /etc/letsencrypt/live/mydomain.com/fullchain.pem; # managed by Certbot    ssl_certificate_key /etc/letsencrypt/live/mydomain.com/privkey.pem; # managed by Certbot    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot}

And my waitress application below:

    def start(self):        # Start the database instance        self.db.start()        # Set the DEBUG flag to False in production mode        self.application.app.config["DEBUG"] = False        # Store a reference to the application instance        app_instance = self.application.app        # If we are in production mode        if self.prod:            # Set the host to "0.0.0.0" (all network interfaces) and the port to 8080            url = "127.0.0.1:80"            # Print the URL that the application is running on            print(f"Running PROD: http://{url}")            # Start the application with Waitress, a production-ready WSGI server            # The number of threads is set to 40            self.register()            waitress.serve(app_instance, listen=url, threads=10)        else:            # If we are in development mode            print("Running DEV")            # Run the application with its built-in development server            # The host is set to "0.0.0.0" (all network interfaces), the port is 8080,            # and debug mode is enabled            self.register()            self.application.run(host="127.0.0.1", port=80, debug=True,url_scheme='https', threaded=True)

What I am having trouble with, the webpage previously returned error 400 header size issues hence I specified a large_client_header_buffers object, and now it seems to return error 500 continuously.

And the most recent logs from nginx are as follows:

2024/06/21 20:15:03 [alert] 2935#2935: *48088 socket() failed (24: Too many open files) while connecting to upstream, client: 127.0.0.1, server: mydomain.com, request: "GET / HTTP/1.0", upstream: "http://127.0.0.1:80/", host: "mydomain.com"

I have got the flask app setup to run on crontab when the system boots, and NGINX also starts on boot.

Any help at all would be appreciated!