System requirements

Functional:

1. The system should expose an API for creating a shortcut, let's say "/api/create" with a payload containing an original URL.

2. The system should redirect a user to an original URL once he sends a request to the shortcut, say "/api/".

3. There should be a UI page for the user to interact with when creating a new request. For example, an input field.

Non-Functional:

1. The system should be scalable. In case, the number of requests per minute grows, we could add more machines and therefore increase the throughput.
2. The system should be highly performant, so the user doesn't have to wait for their shortcut to be created and for the redirections.
3. The system should guarantee high availability, so there is no single point of failure.
4. Durability is very important in order to avoid losing the users' shortcuts.
5. The system should be easy to maintain.
6. The cost of building and maintaining this system should be as low as possible.

I could add a data consistency requirement, but since availability and consistency are self-excluding things because of the CAP theorem, in the case of the URL shortening service, availability is more important so millions of users aren't blocked by the service.

Capacity estimation

Estimate the scale of the system you are going to design...

API design

1. SEND request to "/api/create".

The payload example:

{"original_url": "https://www.youtube.com/watch/fJiw8Lfj"}

The response example:

{"result": "jw3fJFoJmqDSa"}

The UI will add an address of our service as a prefix to the result of the API.

2. GET request to "/".

This request should be redirected to the original URL.

Database design

Defining the system data model early on will clarify how data will flow among different components of the system. Also you could draw an ER diagram using the diagramming tool to enhance your design...

High-level design

You should identify enough components that are needed to solve the actual problem from end to end. Also remember to draw a block diagram using the diagramming tool to augment your design. If you are unfamiliar with the tool, you can simply describe your design to the chat bot and ask it to generate a starter diagram for you to modify...

Request flows

Explain how the request flows from end to end in your high level design. Also you could draw a sequence diagram using the diagramming tool to enhance your explanation...

Detailed component design

Dig deeper into 2-3 components and explain in detail how they work. For example, how well does each component scale? Any relevant algorithm or data structure you like to use for a component? Also you could draw a diagram using the diagramming tool to enhance your design...

Trade offs/Tech choices

Explain any trade offs you have made and why you made certain tech choices...

Failure scenarios/bottlenecks

Try to discuss as many failure scenarios/bottlenecks as possible.

Future improvements

What are some future improvements you would make? How would you mitigate the failure scenario(s) you described above?