I'm looking at the WSGI specification and I'm trying to figure out how servers like uWSGI fit into the picture. I understand the point of the WSGI spec is to separate web servers like nginx from web applications like something you'd write using Flask. What I don't understand is what uWSGI is for. Why can't nginx directly call my Flask application? Can't flask speak WSGI directly to it? Why does uWSGI need to get in between them?
There are two sides in the WSGI spec: the server and the web app. Which side is uWSGI on?
Okay, I think I get this now.
Why can't nginx directly call my Flask application?
Because nginx doesn't support the WSGI spec. Technically nginx could implement the WSGI spec if they wanted, they just haven't.
That being the case, we need a web server that does implement the spec, which is what the uWSGI server is for.
Note that uWSGI is a full fledged http server that can and does work well on its own. I've used it in this capacity several times and it works great. If you need super high throughput for static content, then you have the option of sticking nginx in front of your uWSGI server. When you do, they will communicate over a low level protocol known as uwsgi.
"What the what?! Another thing called uwsgi?!" you ask. Yeah, it's confusing. When you reference uWSGI you are talking about an http server. When you talk about uwsgi (all lowercase) you are talking about a binary protocol that the uWSGI server uses to talk to other servers like nginx. They picked a bad name on this one.
For anyone who is interested, I wrote a blog article about it with more specifics, a bit of history, and some examples.
NGINX in this case only works as a reverse proxy and render static files not the dynamic files, it receives the requests and proxies them to the application server, that would be UWSGI.
The UWSGI server is responsible for loading your Flask application using the WSGI interface. You can actually make UWSGI listen directly to requests from the internet and remove NGINX if you like, although it's mostly used behind a reverse proxy.
From the docs:
uWSGI supports several methods of integrating with web servers. It is also capable of serving HTTP requests by itself.
WSGI is just an interface specification, in simple terms, it tells you what methods should be implemented for passing requests and responses between the server and the application. When using frameworks such as Flask or Django, this is handled by the framework itself.
In other words, WSGI is basically a contract between python applications (Flask, Django, etc) and web servers (UWSGI, Gunicorn, etc). The benefit is that you can change web servers with little effort because you know they comply with the WSGI specification, which is actually one of the goals, as stated in PEP-333.
Python currently boasts a wide variety of web application frameworks, such as Zope, Quixote, Webware, SkunkWeb, PSO, and Twisted Web -- to name just a few 1. This wide variety of choices can be a problem for new Python users, because generally speaking, their choice of web framework will limit their choice of usable web servers, and vice versa.
A traditional web server does not understand or have any way to run Python applications. That's why WSGI server come in. On the other hand Nginx supports reverse proxy to handle requests and pass back responses for Python WSGI servers.
This link might help you: https://www.fullstackpython.com/wsgi-servers.html
There is an important aspect which we are missing . Flask and Django are web frameworks and we build web applications out of them . uWSGI or Gunicorn process the framework files . Consider it as a software application sitting in between the Django app and Nginx . uWSGI and Nginx communicate using WSGI but there is no communication interface between Django and uWSGI . Check out this video https://www.youtube.com/watch?v=WqrCnVAkLIo
In simple terms, just think of an analogy where you are running a CGI or PHP application with Nginx web server. You will use the respective handlers like php-fpm to run these files since the webserver, in its native form doesn't render these formats.
Related
I knew that for deploying a Django application we have to use a combination of uWSGI + Nginx or Nginx + Gunicorn server. Is that necessary? I have a small doubt here. Can we deploy the entire application only in Nginx or only in Gunicorn? Will, it not work? Just for an example(leaving production) can't I do that?
For a full pledge application you need both web server and app server. Web server such as nginx or apache deliver static content but app server delivers dynamic content. Major differences between a web server and app server are:
A web server accepts and fulfills requests from clients for static content (i.e., HTML pages, files, images, and videos) from a website. Web servers handle HTTP requests and responses only.
An application server exposes business logic to the clients, which generates dynamic content. It is a software framework that transforms data to provide the specialized functionality offered by a business, service, or application. Application servers enhance the interactive parts of a website that can appear differently depending on the context of the request.
To know more please follow these link:
https://www.ibm.com/cloud/learn/web-server-vs-application-server
https://www.educative.io/edpresso/web-server-vs-application-server
YES , you can. NO, you shouldn't.
If you run your app (in my case Django), on its development server. You can access it from a remote computer at its ip_address:port_number which should look something like 123.142.524.110:8000 and you can see your app at work.
You can also run Django with only gunicorn, it will still lack the web servers capabilities like sering static files efficiently or handling slow clients or DDOS handling. But it will run and that is all I can promise.
Unsure of whether Nginx can be directly tried with DJANGO app server, but I don't see why not. <<Probably someone else can attest to having successfully 'tried' it>>
I should repeat again, just coz its possible doesn't mean you should do it.
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.
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.
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.
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.