/usr/bin/gunicorn -c /usr/local/panel/gunicorn.config.py app:app

gunicorn.config.py

# Gunicorn configuration file
# https://docs.gunicorn.org/en/stable/configure.html#configuration-file
# https://docs.gunicorn.org/en/stable/settings.html

import multiprocessing
from gunicorn.config import Config

# Create a Gunicorn configuration object
config = Config()

# Listen on port 2083 for both HTTP and HTTPS
bind = ["0.0.0.0:2083"]

backlog = 2048
workers = multiprocessing.cpu_count() * 2 + 1

# Use gevent worker class
worker_class = 'gevent'
worker_connections = 1000
timeout = 30
graceful_timeout = 30
keepalive = 2
max_requests = 1000
max_requests_jitter = 50
pidfile = 'openpanel'

# Middleware for routing based on the hostname
def hostname_middleware(environ, start_response):
    # Check the hostname from the request
    hostname = environ.get('HTTP_HOST', '')

    if 'openpanel.co' in hostname:
        # Use HTTPS on port 2083
        environ['wsgi.url_scheme'] = 'https'
    else:
        # Use HTTP on port 2083
        environ['wsgi.url_scheme'] = 'http'

    return app(environ, start_response)

# SSL settings
certfile = '/etc/live/ssl_certificate.crt'
keyfile = '/etc/live/ssl_private_key.key'
ssl_version = util.ssl.PROTOCOL_TLS

def post_fork(server, worker):
    server.log.info("Worker spawned (pid: %s)", worker.pid)

def pre_fork(server, worker):
    pass

def pre_exec(server):
    server.log.info("Forked child, re-executing.")

def when_ready(server):
    server.log.info("Server is ready. Spawning workers")

def worker_int(worker):
    worker.log.info("worker received INT or QUIT signal")

errorlog = '/var/log/openpanel/error.log'
loglevel = 'info'
accesslog = '/var/log/openpanel/access.log'
access_log_format = '%(h)s %(l)s %(u)s %(t)s "%(r)s" %(s)s %(b)s "%(f)s" "%(a)s"'

# Application reference
app = app:app

# Add the hostname middleware
application = hostname_middleware


# Allow specific IP addresses
#config.allow_ip = ['192.168.1.100']

Run with
cd /usr/local/panel/ && /usr/bin/gunicorn -c /usr/local/panel/gunicorn_config.py app:app