Auto reloading Flask app when source code changes
Solution 1
The issue here, as stated in other answers, is that it looks like you moved from python run.py
to foreman start
, or you changed your Procfile
from
# Procfile
web: python run.py
to
# Procfile
web: gunicorn --log-level=DEBUG run:app
When you run foreman start
, it simply runs the commands that you've specified in the Procfile
. (I'm going to guess you're working with Heroku, but even if not, this is nice because it will mimic what's going to run on your server/Heroku dyno/whatever.)
So now, when you run gunicorn --log-level=DEBUG run:app
(via foreman start
) you are now running your application with gunicorn
rather than the built in webserver that comes with Flask
. The run:app
argument tells gunicorn
to look in run.py
for a Flask
instance named app
, import it, and run it. This is where it get's fun: since the run.py
is being imported, __name__ == '__main__'
is False
(see more on that here), and so app.run(debug = True, port = 5000)
is never called.
This is what you want (at least in a setting that's available publicly) because the webserver that's built into Flask
that's used when app.run()
is called has some pretty serious security vulnerabilities. The --log-level=DEBUG
may also be a bit deceiving since it uses the word "DEBUG" but it's only telling gunicorn
which logging statements to print and which to ignore (check out the Python docs on logging.)
The solution is to run python run.py
when running the app locally and working/debugging on it, and only run foreman start
when you want to mimic a production environment. Also, since gunicorn
only needs to import the app
object, you could remove some ambiguity and change your Procfile
to
# Procfile
web: gunicorn --log-level=DEBUG app:app
You could also look into Flask Script which has a built in command python manage.py runserver
that runs the built in Flask webserver in debug mode.
Solution 2
The solution was to stop using foreman start
as stated in the comments and directly execute python run.py
.
This way, the app.run
method with the debug=True
and use_reloader=True
configuration parameters take effect.
Solution 3
Sample Application where app is our application and this application had been saved in the file start.py:
from flask import Flask
app = Flask(__name__)
@app.route('/')
def hallo():
return 'Hello World, this is really cool... that rocks... LOL'
now we start the application from the shell with the flag --reload
gunicorn -w 1 -b 127.0.0.1:3032 start:app --reload
and gunicorn reloads the application at the moment the file has changed automaticly. No need to change anything at all.
if you'd love to run this application in the background add the flag -D
gunicorn -D -w 1 -b 127.0.0.1:3032 start:app --reload
-D Demon mode
-w number of workers
-b address and port
start (start.py) :app - application
--reload gunicorns file monitoring
Look at the settings file: http://docs.gunicorn.org/en/latest/settings.html
all options and flags are mentioned there. Have fun!
HanSooloo
Updated on August 16, 2020Comments
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HanSooloo almost 4 years
I know for a fact that Flask, in debug mode, will detect changes to .py source code files and will reload them when new requests come in.
I used to see this in my app all the time. Change a little text in an @app.route decoration section in my views.py file, and I could see the changes in the browser upon refresh.
But all of a sudden (can't remember what changed), this doesn't seem to work anymore.
Q: Where am I going wrong?
I am running on a OSX 10.9 system with a VENV setup using Python 2.7. I use
foreman start
in my project root to start it up.App structure is like this:
[Project Root] +-[app] | +-__init__.py | +- views.py | +- ...some other files... +-[venv] +- config.py +- Procfile +- run.py
The files look like this:
# Procfile web: gunicorn --log-level=DEBUG run:app
# config.py contains some app specific configuration information.
# run.py from app import app if __name__ == "__main__": app.run(debug = True, port = 5000)
# __init__.py from flask import Flask from flask.ext.login import LoginManager from flask.ext.sqlalchemy import SQLAlchemy from flask.ext.mail import Mail import os app = Flask(__name__) app.config.from_object('config') db = SQLAlchemy(app) #mail sending mail = Mail(app) lm = LoginManager() lm.init_app(app) lm.session_protection = "strong" from app import views, models
# app/views.py @app.route('/start-scep') def start_scep(): startMessage = '''\ <html> <header> <style> body { margin:40px 40px;font-family:Helvetica;} h1 { font-size:40px; } p { font-size:30px; } a { text-decoration:none; } </style> </header> <p>Some text</p> </body> </html>\ ''' response = make_response(startMessage) response.headers['Content-Type'] = "text/html" print response.headers return response
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user2682863 about 4 yearsjust note that --reload is incompatible with the preload option docs.gunicorn.org/en/latest/settings.html#reload