System requirements

Functional:

1. Creating a short URL from a long URL
2. Retrieving the long URL from short URL
3. System should validate long URL:
   1. Format checking - ensure that the URL follows a valid format
   2. Reachability check (optional)
   3. Length check - we may want to set maximum limit on the length of the URL
4. Provide analytics:
   1. Amount of clicks on the links

Non-Functional:

1. Availability - the service should be highly available. Target uptime - 99.9%
2. Performance:
   1. retrieving a long URL from should should take ideally less then 10 ms
   2. creating a short URL should take less than 10 sec
3. Scalability:
   • The service should be able to handle a growing number of requests over time. You might estimate traffic to include:
     • Around 200 requests per second for creating short URLs.
     • Up to 20,000 requests per second for redirecting from short URLs to long URLs.
4. Data Persistence
   • Ensure that all mappings between short and long URLs are stored reliably, avoiding any data loss

Capacity estimation

Single entry:

1. Long URL: 100 bytes
2. Short URL: 8 bytes
3. Created time: 8 bytes
4. User ID: 16 bytes

Total: 132 bytes, rounding to 144 bytes.

Create RPS: 200 req/sec => 2.5GB/day

Storage per day: 2.5GB

Storage per year: 1TB

Network bandwidth:

Create: 28kb/s

Read: 2.8Mb/s

There is bandwidth for HTTP requests and DB queries, hence doubling:

Create 56kb/s, Read: 6MB/s

If peak load doubles, total bandwidth is ~13MB/s

API design

Create user

POST `/v1/users`

Body:

Response:

201 Created

Create short link

POST `/v1/links`

Accepts a body with url, user_id, and optional custom_short_url to create a new short link.

Body:

"url": string, starting with `http://` or `https://`, with max length 512 bytes.

"user_id": alpanumerical user ID

"custom_short_url": custom link ID - 8 chars. If custom_short_url is not provided, ID is generated automatically.

Response:

201 Created

400 Bad Request - for invalid URL (invalid scheme, missing domain, exceeding max length, etc).

409 Conflict - if provided `custom_short_url` is already used.

When a user attempts to generate a short URL for an already existing long URL, already existing short URL is returned.

Get long URL

GET `/v1/links/{ID}`

GET /v1/links/{ID}: Takes a short_url ID and returns the corresponding long URL with additional metadata, if applicable.

Response:

200 OK

404 Not found

Get links for user

GET `/v1/users//links?limit=N&cursor=CURSOR`

Allows fetching all links associated with a given user_id, with pagination support (e.g., limit and cursor).

Response:

Database design

Indexing

1. Index on short_url in URL_MAPPING for quick retrieval by short URL
2. Index on user_id in URL_MAPPINGfor quick retrieval of links by user ID.

High-level design

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?