System requirements

Functional:

• User enters a url and gets a shorter version of it.
• Multiple users should be able to shorten the same url if needed.
• Variable url longevity.
• User accounts for url management and keeping records.

Non-Functional:

• Availability: generated urls should be immediately available.
• Security: original urls could be private ones, therefore there should be a decent level of access security to them.

Capacity estimation

Let's assume we'll have around 10,000 URL shortening requests per day. Each shortened URL can be used multiple times, so we'll multiply that by a factor of 10 (10,000 URLs x 10 redirection requests), assuming each user makes 10 redirection requests per day on a shortened URL.

For storage, each original URL might be up to 100 characters (100 bytes), and each shortened URL will be around 25 characters (25 bytes).

With 10,000 shortening requests per day, we can easily expect up to 1,000,000 shortened URLs per month:

100 x 1000000 = 100.000.000 bytes - 100 MB

25 x 1000000 = 25.000.000 bytes - 25 MB

We do not know at this point what will be the user growth over time, so we can go for a noSQL database for storage, to allow horizontal scaling.

To make this more fault tolerant, we should multiply the storage estimations by two and create a clone of the main cluster

API design

Define what APIs are expected from the system...

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?