My Flask stops responding when uploading files or when collecting data from another server via GET. I assume, the problem is, that Flask is only running on one thread.
How can I change this, so multiple users can use the site?
Flask's development webserver (invoked when you use app.run) is not a production web server.
Quoting the docs:
You can use the builtin server during development, but you should use a full deployment option for production applications. (Do not use the builtin development server in production.)
If you want to use Flask in a production environment take a look at the deployment options suggested by the documentation.
For testing purposes with small applications that are doing slightly complicated things I deploy the code I'm developing behind CherryPy using this snippet. (The only disadvantage of this pattern is you loose access to Werkzeug's debugger.)
Related
I want to use GCP cloud run as a technology to run my python flask app, so I have to dockerize it. Most of examples I've seen are either using built in flask server or gunicorn server as an ENTRYPOINT, which gives a warning on a console, that it shouldn't be used on production.
My question is: does it matter with a platform like GCP cloud run which server do I use to run that code? What would be the performance impact of that choice?
You want gunicorn, and you'll need to configure it correctly.
Typically in these setups there will be an external HTTP server proxying requests to your server. So it matters rather less which webserver you're using on the backend, because it's not directly exposed.
That being said, the built-in Flask webserver isn't ideal, so gunicorn would probably be better. You will need to tweak Gunicorn's settings slightly to work correctly in container: logging, heartbeat setting, and parallelism.
See https://pythonspeed.com/articles/gunicorn-in-docker/ for details.
Setting up Flask with uWSGI and Nginx can be difficult. I tried following this DigitalOcean tutorial and still had trouble. Even with buildout scripts it takes time, and I need to write instructions to follow next time.
If I don't expect a lot of traffic, or the app is private, does it make sense to run it without uWSGI? Flask can listen to a port. Can Nginx just forward requests?
Does it make sense to not use Nginx either, just running bare Flask app on a port?
When you "run Flask" you are actually running Werkzeug's development WSGI server, and passing your Flask app as the WSGI callable.
The development server is not intended for use in production. It is not designed to be particularly efficient, stable, or secure. It does not support all the possible features of a HTTP server.
Replace the Werkzeug dev server with a production-ready WSGI server such as Gunicorn or uWSGI when moving to production, no matter where the app will be available.
The answer is similar for "should I use a web server". WSGI servers happen to have HTTP servers but they will not be as good as a dedicated production HTTP server (Nginx, Apache, etc.).
Flask documents how to deploy in various ways. Many hosting providers also have documentation about deploying Python or Flask.
First create the app:
import flask
app = flask.Flask(__name__)
Then set up the routes, and then when you want to start the app:
import gevent.pywsgi
app_server = gevent.pywsgi.WSGIServer((host, port), app)
app_server.serve_forever()
Call this script to run the application rather than having to tell gunicorn or uWSGI to run it.
I wanted the utility of Flask to build a web application, but had trouble composing it with other elements. I eventually found that gevent.pywsgi.WSGIServer was what I needed. After the call to app_server.serve_forever(), call app_server.stop() when to exit the application.
In my deployment, my application is listening on localhost:port using Flask and gevent, and then I have Nginx reverse-proxying HTTPS requests to it.
You definitely need something like a production WSGI server such as Gunicorn, because the development server of Flask is meant for ease of development without much configuration for fine-tuning and optimization.
Eg. Gunicorn has a variety of configurations depending on the use case you are trying to solve. But the development flask server does not have these capabilities. In addition, these development servers show their limitations as soon as you try to scale and handle more requests.
With respect to needing a reverse proxy server such as Nginx is concerned it depends on your use case.
If you are deploying your application behind the latest load balancer in AWS such as an application load balancer(NOT classic load balancer), that itself will suffice for most use cases. No need to take effort into setting up NGINX if you have that option.
The purpose of a reverse proxy is to handle slow clients, meaning clients which take time to send the request. These reverse load balancers buffer the requests till the entire request is got from the clients and send them async to Gunicorn. This improves the performance of your application considerably.
I have successfully developed a Django app. The requirement is to deploy the app over an on-premise server. The application is accessible on the intranet using the development environment. Is any web server is preferred to deploy this application locally (or) should I leave the terminal running the server as it is so that the users can access the application as they are already doing it? I am using a unix server.
If the question is actually on deployment model, I suggest to take a look at django docs on deployment. Depending on load, uWSGI/Gunicorn [+ nginx] will be good choice.
Independent of tools you use, no need to leave running terminal on your server. There's a lot of tools to "daemonize" processes. Simplest would be supervisor
Setting up Flask with uWSGI and Nginx can be difficult. I tried following this DigitalOcean tutorial and still had trouble. Even with buildout scripts it takes time, and I need to write instructions to follow next time.
If I don't expect a lot of traffic, or the app is private, does it make sense to run it without uWSGI? Flask can listen to a port. Can Nginx just forward requests?
Does it make sense to not use Nginx either, just running bare Flask app on a port?
When you "run Flask" you are actually running Werkzeug's development WSGI server, and passing your Flask app as the WSGI callable.
The development server is not intended for use in production. It is not designed to be particularly efficient, stable, or secure. It does not support all the possible features of a HTTP server.
Replace the Werkzeug dev server with a production-ready WSGI server such as Gunicorn or uWSGI when moving to production, no matter where the app will be available.
The answer is similar for "should I use a web server". WSGI servers happen to have HTTP servers but they will not be as good as a dedicated production HTTP server (Nginx, Apache, etc.).
Flask documents how to deploy in various ways. Many hosting providers also have documentation about deploying Python or Flask.
First create the app:
import flask
app = flask.Flask(__name__)
Then set up the routes, and then when you want to start the app:
import gevent.pywsgi
app_server = gevent.pywsgi.WSGIServer((host, port), app)
app_server.serve_forever()
Call this script to run the application rather than having to tell gunicorn or uWSGI to run it.
I wanted the utility of Flask to build a web application, but had trouble composing it with other elements. I eventually found that gevent.pywsgi.WSGIServer was what I needed. After the call to app_server.serve_forever(), call app_server.stop() when to exit the application.
In my deployment, my application is listening on localhost:port using Flask and gevent, and then I have Nginx reverse-proxying HTTPS requests to it.
You definitely need something like a production WSGI server such as Gunicorn, because the development server of Flask is meant for ease of development without much configuration for fine-tuning and optimization.
Eg. Gunicorn has a variety of configurations depending on the use case you are trying to solve. But the development flask server does not have these capabilities. In addition, these development servers show their limitations as soon as you try to scale and handle more requests.
With respect to needing a reverse proxy server such as Nginx is concerned it depends on your use case.
If you are deploying your application behind the latest load balancer in AWS such as an application load balancer(NOT classic load balancer), that itself will suffice for most use cases. No need to take effort into setting up NGINX if you have that option.
The purpose of a reverse proxy is to handle slow clients, meaning clients which take time to send the request. These reverse load balancers buffer the requests till the entire request is got from the clients and send them async to Gunicorn. This improves the performance of your application considerably.
I want to have simple program in python that can process different requests (POST, GET, MULTIPART-FORMDATA). I don't want to use a complete framework.
I basically need to be able to get GET and POST params - probably (but not necessarily) in a way similar to PHP. To get some other SERVER variables like REQUEST_URI, QUERY, etc.
I have installed nginx successfully, but I've failed to find a good example on how to do the rest. So a simple tutorial or any directions and ideas on how to setup nginx to run certain python process for certain virtual host would be most welcome!
Although you can make Python run a webserver by itself with wsgiref, I would recommend using one of the many Python webservers and/or web frameworks around. For pure and simple Python webhosting we have several options available:
gunicorn
tornado
twisted
uwsgi
cherrypy
If you're looking for more features you can look at some web frameworks:
werkzeug
flask
masonite
cherrypy (yes, cherrypy is both a webserver and a framework)
django (for completeness, I know that was not the purpose of the question)
You should look into using Flask -- it's an extremely lightweight interface to a WSGI server (werkzeug) which also includes a templating library, should you ever want to use one. But you can totally ignore it if you'd like.
You can use thttpd. It is a lightweight wsgi server for running cgi scripts. It works well with nginx. How to setup thttpd with Nginx is detailed here: http://nginxlibrary.com/running-cgi-scripts-using-thttpd/
All the same you must use wsgi server, as nginx does not support fully this protocol.