This is a bog standard Django + DRF (https://www.django-rest-framework.org/) app.

Best way to proceed:

1. mkvirtualenv shortz
2. pip install -r requirements.txt
3. (cd shortz/ && ./manage.py migrate)
4. (cd shortz/ && ./manage.py runserver)
5. ready for testing

There are no unit tests, as those were not required. You can test the app using client of your choice (curl, Postman, restclient from Emacs what have you).

Here I'm showing result of using httpie per https://github.com/jakubroztocil/httpie#json

Valid URL shortening

$ http POST http://127.0.0.1:8000/shorten_url/ url=https://github.com/qazwsxpawel/

HTTP/1.1 201 Created
Allow: OPTIONS, POST
Content-Length: 181
Content-Type: application/json
Date: Tue, 31 Jul 2018 14:19:37 GMT
Server: WSGIServer/0.2 CPython/3.6.2
Vary: Accept, Cookie
X-Frame-Options: SAMEORIGIN

{
    "code": "oLMpI6NRP8GhPKoPa_UKUg",
    "date_created": "2018-07-31T14:19:37.074597Z",
    "shortened_url": "http://localhost:8000/oLMpI6NRP8GhPKoPa_UKUg",
    "url": "https://github.com/qazwsxpawel/"
}

Invalid URL handling

$ http POST http://127.0.0.1:8000/shorten_url/ url=https://github/qazwsxpawel/

HTTP/1.1 400 Bad Request
Allow: OPTIONS, POST
Content-Length: 30
Content-Type: application/json
Date: Tue, 31 Jul 2018 14:21:22 GMT
Server: WSGIServer/0.2 CPython/3.6.2
Vary: Accept, Cookie
X-Frame-Options: SAMEORIGIN

{
    "url": [
        "Enter a valid URL."
    ]
}

Retrieval

Open the returned URL in the browser (here: "http://localhost:8000/oLMpI6NRP8GhPKoPa_UKUg") and enjoy the redirect :)

Not being an expert in the area I would apply this simple formula:

• Load balancing
• Placing API behind server-side cache e.g. Varnish ("a caching HTTP reverse proxy")
• Caching the DB + ORM lookups

Next would be measuring bottlenecks in this simple application if any left (the biggest being the DB lookup).

1. Make the URL's actually short (those are OK, but not something you would like to type out)
2. Fix TODO's