System requirements

Functional:

1. Ability to take the URL and return a shorter format of this URL

Non-Functional:

1. Availability over consistency -> We want the service to be available over consistent
2. Low latency. We want our tiny URL to provide as minimal overhead as possible
3. Available in multiple regions in the world

Capacity estimation

1. Assuming we are going to get 100 reads per second and 1 write per second.
2. Assuming 1 write per second, to encode the URL we would need 8 bytes of data. Assuming 10 ^ 5 seconds in a day, that gives us 8 * 10 ^ 5 Bytes of data a day, which is about about 800KB of data a day. Every year we will need 800KB * ~400Days = 320,000 = 320MB worth of storage needed per year
3. We will need multiple servers to handle 100 requests per second

API design

We would want to have 2 types of APIs - one API would serve to get the request and the URL.

The API would redirect the sender to the actual resource and on success return 302 (redirected) or fail on something like 404

The other API would let the user encode their URL in the UI portal. We should allow them to specify the URL themselves which can be hashed easily to locate where the URL is stored

Database design

The ideal database for this system would be key-value value based. Because each URL will have a unique hash we can use that as our key. A NoSQL database would work perfectly for this design because they can be key-value based and are very scalable.

High-level design

1. The clients will hit our load balancers where it will redirect the request to one of our application servers
2. Our application servers will then check our in-memory cache (Redis) to see if the hashed key exists. The cache server is LRU
   1. For scalability we can have multiple cache servers. For the application server to know which cache server the request belongs to we will have a cache client daemon running in each applications server, which uses consistent hashing to determine which cache server to check.
3. If we get a hit from our cache server, we will return the result. If we do not, then we will check the database. NoSQL database would be able to route the request tot eh correct partition and return the request. If not present, we return 404

Overall, I am okay with after the resource is added, that it takes some time for it to fully propogate to all DB replicas because eventual consistency is OK. However, we want to keep durability (write requests) and latency (making redirect as quickly as possible)

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?