Deploy Flask Applications with uWSGI and Lighttpd

04 Oct, 2020

This text is mainly documentation for me. It may apply to others, though.

In this text, I describe how you can deploy Python applications with Flask and Lighttpd. The main idea is that Lighttpd serves static files from a directory and dynamic requests from a Flask backend. This description easily translates to other backends (i.e., Tomcat). This has the advantage that you only have to configure TLS once in Lighttpd, or Lighttpd can be behind a proxy itself.

Flask and uWSGI

For this text, I assume a working Flask application (i.e., this minimal example). First, you install uWSGI and the required Python packages using PIP: pip install uwsgi flask. Then, you create a user that runs uWSGI: useradd -r -m uwsgi and place all Flask files in its directory.

Systemd is going to manage the Flask application. Hence, you create a flask.ini file in the app directory:

[uwsgi]
module = wsgi
master = true
processes = 3
http = 127.0.0.1:8000

The Systemd unit file looks like this:

[Unit]
Description=uWSGI server for flaskdemo
After=network.target
[Service]
User=uwsgi
Group=uwsgi
WorkingDirectory=/home/uwsgi/backend/
Environment="PATH=/home/uwsgi/backend/"
ExecStart=/home/uwsgi/backend/uwsgi --ini flask.ini
[Install]
WantedBy=multi-user.target

Now you can start uWSGI and check whether the Flask application runs correctly: systemctl start flask.service. If so, you enable the uWSGI service permanently systemctl enable flask.service.

Lighttpd

In the next part, you configure Lighttpd as a proxy for uWSGI. I assume a running Lighttpd server.

You configure the proxy using the proxy module (mod_proxy). Therefore, you put the following in /etc/lighttpd/conf.d/proxy.conf:

$HTTP["url"] =~ "^/app/backend/" {
  proxy.header = ("map-urlpath" => ("/app/backend/" => "/"))
  proxy.server = ( "" =>
    (
      ("host" => "127.0.0.1", "port" => 8000)
    )
  )
}

The module rewrites all URLs that end with "/app/backend/" to "/" and redirects them to the Flask app. To activate the proxy module, add it to the Lighttpd configuration file (/etc/lighttpd/lighttpd.conf) and restart the webserver:

systemctl restart lighttpd.service

History of Document

2020-10-04 Initial text
2021-07-04 Move text to blog