Subdomain in Flask | Python

Prerequisite: Introduction to Flask

In this article, we will learn how to setup subdomains in Flask. But first, let’s go through the basic like what is DNS and subdomains.

Domain Name System (DNS):
The Domain Name System (DNS) is a hierarchical and decentralized naming system for computers, services, or other resources connected to the Internet or a private network. Most prominently, it translates more readily memorized domain names to the numerical IP addresses needed for locating and identifying computer services and devices with the underlying network protocols.
DNS is basically using words (Domain Names) in place of numbers (IP addresses) to locate something. For example, 127.0.0.1 is used to point the local computer address, localhost.



Subdomain:
A subdomain is a domain that is part of a larger domain. Basically, it’s a sort of child domain which means it is a part of some parent domain. For example, practice.geeksforgeeks.org and contribute.geeksforgeeks.org are subdomains of the geeksforgeeks.org domain, which in turn is a subdomain of the org top-level domain (TLD).
These are different from the path defined after TLD as in geeksforgeeks.org/basic/.

Further, we will discuss how to set endpoints in your web application using Python’s micro-framework, Flask.

Adding alternate domain name for local IP –
Prior to the coding part, we got to setup hosts file in order to provide alternate names to local IP so that we are able to test our app locally. Edit this file with root privileges.

Linux: /etc/hosts 
Windows: C:\Windows\System32\Drivers\etc\hosts

Add these lines to set up alternate domain names.

127.0.0.1       vibhu.gfg
127.0.0.1       practice.vibhu.gfg

In this example, we’re considering vibhu.gfg as our domain name, with gfg being the TLD. practice would be a subdomain we’re targeting to set in our web app.

Setting up the Server –
In the app’s configuration SERVER_NAME is set to the domain name, along with the port number we intend to run our app on. The default port, flask uses is 5000, so we take it as it is.

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from flask import Flask
  
app = Flask(__name__)
  
  
@app.route('/')
def home():
    return "Welcome to GeeksForGeeks !"
  
  
if __name__ == "__main__":
    website_url = 'vibhu.gfg:5000'
    app.config['SERVER_NAME'] = website_url
    app.run()

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Output:
Run the app and notice the link on which the app is running.

Test the link on your browser.

Adding Several Endpoints –

  1. basic: An endpoint with extension to the path on the main domain.
  2. practice: An endpoint serving on the practice subdomain.
  3. courses: An endpoint with extension on to the path on the practice subdomain.

Subdomains in Flask are set using the subdomain parameter in the app.route decorator.

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from flask import Flask
  
app = Flask(__name__)
  
  
@app.route('/')
def home():
    return "Welcome to GeeksForGeeks !"
  
  
@app.route('/basic/')
def basic():
    return "Basic Category Articles " \
           "listed on this page."
  
  
@app.route('/', subdomain ='practice')
def practice():
    return "Coding Practice Page"
  
  
@app.route('/courses/', subdomain ='practice')
def courses():
    return "Courses listed " \
           "under practice subdomain."
  
  
if __name__ == "__main__":
    website_url = 'vibhu.gfg:5000'
    app.config['SERVER_NAME'] = website_url
    app.run()

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Output:



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