System requirements

Functional:

1. User could get short url given a long original url
2. User should be able to be directed to original long url given shorten url
3. The generated shorten url should be unique for each long URL
4. The shorten URL should be readable, so only contains lower and upper case letters and digits

Non-Functional:

1. The system should have hight availability, we could achieve that by having multiple instances of our web server
2. The system should be scalable to handle large volume of request by user, for this part, we could shard our database
3. The system should have small latency，we could use cache to reduce the time for reading, for example, we could use Redis
4. The system should have persistency, we could have back-up web server for our service

Capacity estimation

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

API design

createShortenURL(originalURL string, expireDate Optional[String]) -> None

getOriginalURL(shortURL string) -> String

// Delete the shorten url of the given long url)

deleteURL(longURL string)

Database design

CREATE TABLE User (

UserId INT NOT NULL PRIMARY KEY,

UserName VARCHAR(255) NOT NULL,

UserEmail VARCHAR(255) NOT NULL,

AuthToken VARCHAR(255) NOT NULL

)

CREATETABLE URLMapping ( shortenURL VARCHAR(255) NOTNULLUNIQUE, OriginalURL VARCHAR(2048) NOTNULL, CreatedGMT DATETIME NOTNULL, ExpireGMT DATETIME );

High-level design

The users request first go to the client service, which does the authentication process, we could have a rate limiter to protect our system from melicious behavior

If the request pass the auth and rate limiter check, it will go to nginx, to distribute the request to one of webservers

We could have an offline key generator service to generate the keys for shorten urls, and store the generated keys to key db, whenever the request needs new short url, we assign the generated key to it, and store them in shortlong url matching table

For getting request, the request will first go to cache, if the cache missing, then it will go to the url maching database, if the url is expired, delete the row, otherwise return the original url

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?