On Tuesday, February 26, 2019 at 3:13:00 PM UTC-7, Tal wrote:
Is it right though?
On Tuesday, February 26, 2019 at 2:49:03 PM UTC-7, mike wrote:
Great write up!
On Tue, Feb 26, 2019 at 2:39 PM Tal <tal....@gmail.com> wrote:
Did I get something wrong?
Do you mean the devs working on the Django project know
nothing about this, or the devs using Django to build web
apps?
From what I've read, devs using Django don't need to be
too familiar with WSGI, but it seems like it helps at
least having a conceptual understanding of what it is.
On Tuesday, February 26, 2019 at 12:28:26 PM UTC-7, Motaz
Hejaze wrote:
You are very close to what realy happens , most of
devs know nothing aboutbthis stuff
On Tue, 26 Feb 2019, 20:26 Tal, <tal....@gmail.com> wrote:
I've been developing web applications using Flask
and Django for about a year now, and although I've
come across the term WSGI a bunch of times in both
frameworks, I never really understood what it did.
I'm sure I'm not the only one. The quick
explanations I read never made sense to me. Even
PEP3333 didn't really give me a clear picture of
how WSGI fits in with Nginx, and Django. There are
a bunch of articles online that quickly show how
to setup nginx, gunicorn/uwsgi and django to work
in production, and once I figured that out, I
never really had a reason to figure out WSGI
again. But it's been a year now, and I probably
should understand at least the basics.
I did a bit more reading recently, and I think I
get it. Just looking for someone to confirm that
I'm on the right track.
This is how I think it works:
My example uses the most common setup I use:
Nginx, Gunicorn and Django
* When an HTTP request comes in, it hits Nginx first
o Nginx runs multiple processes, and makes
sure that browsers/clients that have a
slow connection don't effect other clients
o If it's a request for a static file, like
a CSS file, JS, image, or anything like
that, Nginx returns it directly
o If it's a request for anything else, it
uses *HTTP* to send the request over a
Unix socket to Gunicorn
+ Doesn't have to be a Unix socket, but
if both Nginx and Gunicorn are running
on the same host, it makes sense to
use Unix sockets
+ The main point is that Nginx uses HTTP
to communicate with Gunicorn
* Gunicorn
o Starts up x worker processes on startup
(as many as you tell it)
o Each worker process imports your
application's code
(django.core.wsgi.get_wsgi_application()
in Django's case)
+ The application's code is a callable
function
+ Gunicorn imports it so that it's ready
to make a function call to it as soon
as an HTTP request comes in
o When an HTTP request comes in from Nginx,
Gunicorn will:
+ Use its main process to assign the
request to a free worker process
+ The worker process translates the HTTP
headers into a python dictionary
(commonly called the 'environment'
dictionary)
+ The worker process makes a function
call to your application, passing it
the 'environment' dictionary, and a
start_response function
* When your application (Django) decides what to
do about the request, and decides to formulate
a response, it will:
o Call start_response, giving it the HTTP
response status (eg. 200 OK), and the HTTP
response headers as a Python object (list
of tuples)
+ Note: At this point, nothing is sent
to the client's browser, or even Nginx yet
o *Return* the body of the response as an
iterable
* Gunicorn will then:
o Add any required HTTP headers the
application didn't provide
o Turn the status, headers and body that it
received from the application into an HTTP
response message
o Send the response back to Nginx using HTTP
* Nginx will then send the response back to the
client
So the job of the individual parts is basically this:
1. Nginx
* Buffers slow clients
* Quickly serves static files
* Possibly handle SSL, if configured
* Passes HTTP requests to Gunicorn (also
using HTTP)
2. Gunicorn
* Deals with TCP connections between nginx
and itself
o Prevents your application from needing
to do lower-level socket stuff with TCP
* Converts HTTP requests into Python
objects, and responses back into HTTP
3. Django
* Just worries about formulating responses
to requests, not keeping track of TCP
connections, or HTTP, or anything low-level
For Apache, they have mod_wsgi, which takes the
place of Gunicorn, acting as a WSGI server.
That sound right? Or am I way off?
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