How does the "builtin server" work with a Flask web application?

Question

http://flask.pocoo.org/docs/1.0/quickstart/#a-minimal-application

$ export FLASK_APP=hello.py
$ python -m flask run
 * Running on http://127.0.0.1:5000/

This launches a very simple builtin server, which is good enough for testing but probably not what you want to use in production.

How does the "very simple builtin server" work with a Flask web application?

• Does the "very simple builtin server" also use WSGI to invoke and communicate with a Flask web application?

• Do the "very simple builtin server" and a Flask web application run in the same or different processes?

If I am correct, an external web server (Apache or Nginx) needs to use WSGI to invoke and communicate a Flask web application, and they run in the same process.

Answer 1

It uses the werkzeug simple WSGI server.

It's a single process, single thread server so if I understand your second question correctly it does not use multiple processes. The app is being served by the same python process that is handling the Flask application.