System requirements

Functional:

• System should take a long URL, ands return to the user a shortened version of this URL
• When the shortened URL is accessed, it should re-direct to the original URL.
• Each shortened URL should be unique while active.

Non-Functional:

• System should be able to handle a high number of redirections

Capacity estimation

I estimate about 200 URL creations per second and about 20,000 URL accesses per second

API design

• shortenUrl - this API takes in a long URL and returns back the shortened version. It is a POST
• redirectUrl - this API takes in a shortened URL and returns back the long URL. It is a GET
• Both API's are restful

Database design

Since read capacity is quite high, we're going to want to go with a NoSQL database, something like DynamoDB or MongoDB. The key-value pair model will work well for our data since the key would be the shortened URL and the value would be the long form URL that we are redirecting to.

High-level design

• First a user calls the shortenUrl API (POST) and passes in the long formed URL that they wish to shorten. The API Gateway will route to a Lambda Function that creates a UUID that will represent the long formed URL
• Once the Lambda Function creates the UUID, it will store the UUID (partition key) into DynamoDB with the long formed URL as the value.
• The user then receives back the shortened URL/UUID.
• When the user accesses the shortened URL, the redirectUrl (GET) API is called.
• The API gateway invokes a Lambda Function that queries the DynamoDB by the UUID (partitionKey) and gets back the long form URL. The API then returns this long form URL to redirect to.
• There should also be a caching layer to cache high traffic short URLs
• We will also need a sweeper to expire and invalidate URL's that have not been accessed in over 1 year.

Request flows

flowchart TD

B["User"];

C{"API Gateway"};

D["Lambda Function"]

E["DynamoDB"];

B --> C;

C --> D;

D --> E;

E --> D;

D --> C;

C --> B;

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?