I intend to use Kubernetes and Ingress for load balancing. I'm trying to learn how to set up Flask, uWSGI and Nginx.
I see this tutorial that has all three installed in the same container, and I'm wondering whether I should use it or not.
https://ianlondon.github.io/blog/deploy-flask-docker-nginx/
I'm guessing the benefit of having them as separate containers and separate pods is that they can then all scale individually?
But also, should Flask and uwsgi even be in separate containers? (or Flask and Gunicorn, since uwsgi seems to be very similar to Gunicorn)
Flask is a web framework, any application written with it needs a WSGI server to host it. Although you could use the Flask builtin developer server, you shouldn't as that isn't suitable for production systems. You therefore need to use a WSGI server such as uWSGI, gunicorn or mod_wsgi (mod_wsgi-express). Since the web application is hosted by the WSGI server, it can only be in the same container, but there isn't a separate process for Flask, it runs in the web server process.
Whether you need a separate web server such as nginx then depends. In the case of mod_wsgi you don't as it uses the Apache web server and so draws direct benefits from that. When using mod_wsgi-express it also is already setup to run in an optimal base configuration and how it does that avoids the need to have a separate front facing web server like people often do with nginx when using uWSGI or gunicorn.
For containerised systems, where the platform already provides a routing layer for load balancing, as is the case for ingress in Kubernetes, using nginx in the mix could just add extra complexity you don't need and could reduce performance. This is because you either have to run nginx in the same container, or create a separate container in the same pod and use shared emptyDir volume type to allow them to communicate via a UNIX socket still. If you don't use a UNIX socket, and use INET socket, or run nginx in a completely different pod, then it is sort of pointless as you are introducing an additional hop for traffic which is going to be more expensive than having it closely bound using a UNIX socket. The uWSGI server doesn't perform as well when accepting requests over INET when coupled with nginx, and having nginx in a separate pod, potentially on different host, can make that worse.
Part of the reason for using nginx in front is that it can protect you from slow clients due to request buffering, as well as other potential issues. When using ingress though, you already have a haproxy or nginx front end load balancer that can to a degree protect you from that. So it is really going to depend on what you are doing as to whether there is a point in introducing an additional nginx proxy in the mix. It can be simpler to just put gunicorn or uWSGI directly behind the load balancer.
Suggestions are as follows.
Also look at mod_wsgi-express. It was specifically developed with containerised systems in mind to make it easier, and can be a better choice than uWSGI and gunicorn.
Test different WSGI servers and configurations with your actual application with real world traffic profiles, not benchmarks which just overload it. This is important as the dynamics of a Kubernetes based system, along with how its routing may be implemented, means it all could behave a lot differently to more traditional systems you may be used to.
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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 am a .net developer coming over to python. I have recently started using Flask and have some quick questions about serving files.
I noticed a lot of tutorials focused on nginix and flask. However, I am able to run flask without nginx. I'm just curious as to why this is used together (nginx and flask). Is nginx only for static files?
Nginx is a proxy server, imagine your apps have multiples microservices on differents languagues.
For more info NGINX REVERSE PROXY
On a development machine flask can be run without a webserver (nginx, apache etc) or an application container (eg uwsgi, gunicorn etc).
Things are different when you want to handle the load on a production server. For starters python is relatively very slow when it comes to serving static content where as apache / nginx do that very well.
When the application becomes big enough to be broken into multiple separate services or has to be horizontally scaled, the proxy server capabilities of nginx come in very handy.
In the architectures I build, nginx serves as the entry point where ssl is terminates and the rest of the application is behind a VPN and firewall.
Does this help?
From http://flask.pocoo.org/docs/1.0/deploying/ :
"While lightweight and easy to use, Flask’s built-in server is not suitable for production as it doesn’t scale well. Some of the options available for properly running Flask in production are documented here."
Tornado is powerful webserver and web Framework written in Python, it can run by its own (stand-alone) or could also be run through an other webserver specially nginx
Is there any performance or advantage of runing Tornado through Nginx ?
Tornado can be run on its own, but there are three major advantages to using nginx as a proxy in front of it:
Nginx is much more efficient at serving static files.
A proxy makes it easier to do rolling restarts of backend processes to perform upgrades without downtime.
Nginx can be configured to more efficiently reject abusive requests (DDoS, etc).
It seems that uwsgi is capable of doing almost anything I am using nginx for: serving static content, execute PHP scripts, host python web apps, ...
So (in order to simplify my environment) can I replace nginx + uwsgi with uwsgi without loss of performance/functionality?
As they say in the documentation:
Can I use uWSGI’s HTTP capabilities in production?
If you need a load balancer/proxy it can be a very good idea. It will
automatically find new uWSGI instances and can load balance in various
ways. If you want to use it as a real webserver you should take into
account that serving static files in uWSGI instances is possible, but
not as good as using a dedicated full-featured web server. If you host
static assets in the cloud or on a CDN, using uWSGI’s HTTP
capabilities you can definitely avoid configuring a full webserver.
So yes, uWSGI is slower than a traditional web server.
Besides performance, in a really basic application you're right, uWSGI can do everything the webserver offers. However, should your application grow/change over time you may find that there are many things the traditional webserver offers which uWSGI does not.
I would recommend setting up deploy scripts in your language of choice (such as Fabric for Python). I would say my webserver is one of the simplest components to deploy & setup in our applications stack, and the least "needy" - it is rarely on my radar unless I'm configuring a new server.
I'm new to linux development. I'm a bit confused on the documentation i read.
My ultimate goal is to host a simple python backed web service that would examine an incoming payload, and forward it to other server. This should be less than 30 lines of code in python.
I'm planning to use nginx to serve up python file. From my research, i also need a python web framework. I chose to go with uwsgi. I'm so confused. which one do I need? an nginx uwsgi module, or uwsgi server? i don't want to put django just for this simple purpose.
the nginx documentation mention that
Do not confuse the uwsgi protocol with the uWSGI server (that speaks the uwsgi protocol)
So, does that mean, i don't need to install uwsgi server separately? do i just install nginx, and start configuring? I'm using nginx 1.4.4
Could someone share a step by step configuration procedure on how to configure uwsgi with nginx, along with a sample python code(hello world maybe)? i can configure nginx just fine, but i don't know how to make it serve python pages. all the docs i could find involves having django on top.
You're mixing up things, so let me clarify.
Python's standard way of publishing applications via web servers is WSGI--you can think of it as a Python's native CGI. uWSGI is a WSGI-compliant server that uses uwsgi protocol to talk to other uWSGI instances or upstream servers. Usually the upstream server is nginx with HttpUwsgiModule that allows it to communicate using uwsgi protocol--with nginx you have additional layer of protection for your app server, load balancing and serving the static files. In most scenarios, You Should Be Using Nginx + UWSGI. To answer your question, uWSGI is installed and run separately from nginx, and they both need to be configured to communicate to each other.
Pure WSGI is pretty low-level, so you may want to use a WSGI-compliant framework. I guess the top two are Django and Flask.
For a hello world Flask setup, Serving Flask With Nginx seems to be a good article.