Python Webservers

Aug 1, 2019
Apr 22, 2020

Programming

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external program outputs HTML instead of plain text, the browser-shell detects it and renders it as a web page. Webserver invokes external programs

A browser is an HTTP client because it sends requests to an HTTP server (Web server), which then sends responses back to the client. The standard (and default) port for HTTP servers to listen on is 80, though they can use any port.

Apache creates processes and threads to handle additional connections. While Nginx is said to be event-driven, asynchronous, and non-blocking.
Nginx includes advanced load balancing and caching abilities.
Nginx is a lot lighter than Apache
Python webframeworks provide simple to use Request-Response structure for HTTP calls
search the codebase grep -i wsgi

WSGI - Web Server Gateway Interface: standardise interface b/w webserver and python applications/frameworks; PEP 333(3); Makes it easy to switch webserver like nginx or apache is they speak the WSGI language

What happens when you click on a URL?

Browser contacts the HTTP web server for demanding the URL
Parsing the URL
Look for the filename
If it finds that file, a request is sent back
Web browser takes a response from the web server
As the server response, it either shows the received file or an error message.

CGI - Common Gateway Interface

Standard how client can communicate with HTTP server. In /usr/lib/cgi-bin directory

Execute programs that execute like command-line-interface programs¹.

It is possible to set up the HTTP server so that whenever a file in a certain directory is requested that file is not sent back; instead it is executed as a program, and whatever that program outputs is sent back for your browser to display. This function is called the Common Gateway Interface or CGI and the programs are called CGI scripts. These CGI programs can be a Python Script, PERL Script, Shell Script, C or C++ program, etc.

Static webserver serves boring static HTML files.
- Session Management not possible
- No dynamic views
Invoke a SCRIPT instead of a FILE. Scripts are saved on server. UNIX like philosohpy, request inputs are set in environment variables. Can use stdout as output
gunicorn talks WSGI language and feeds the framework with requests and responses paameters

Making a python web-server from scratch

Use python sockets

Client Request ----> Nginx (Reverse-Proxy)
                        |
                       /|\
                      | | `-> App. Server I.   127.0.0.1:8081
                      |  `--> App. Server II.  127.0.0.1:8082
                       `----> App. Server III. 127.0.0.1:8083

CGI programming with Python

Generally CGi scripts are installed in cgi-bin folder, for security reasons².


#!/usr/bin/env python

import cgi
import cgitb; cgitb.enable()  # for troubleshooting

print "Content-type: text/html"
print
print """
  <html>
  <head><title>Sample CGI Script</title></head>
  <body>
    <h3> Sample CGI Script </h3>
"""

form = cgi.FieldStorage()
message = form.getvalue("message", "(no message)")
print """
    <p>Previous message: %s</p>
    <p>form
    <form method="post" action="index.cgi">
      <p>message: <input type="text" name="message"/></p>
    </form>
  </body>
  </html>
""" % cgi.escape(message)

Shebang header to invoke python interpreter

Enable traceback from CGI scripts

apt install -y nginx ufw

sudo ufw app list
sudo ufw allow 'Nginx Full'
sudo ufw status

sudo cp -v /path/project/. /var/www/

/etc/nginx
sites-enabled
sites-available

python3 -m http.server --cgi 8000
python -m webbrowser http://localhost:8000/cgi-bin/hello.py

Sample nginx configuration

Security is very important, the user you used to run CGI server will be used to run all the CGi scripts, some of them could be dangerous.

vue + nginx

How to use vue.js with Nginx?

vue.js with docker

try npm run build and then there file be a dist folder. copy the contents of the folder to the server.

Link to project on github

Footnotes

Vue app on nginx on docker