System requirements

Functional:

• create shortened url from long url's
• redirect user to the long URL given a short URL
• custom alias support for branded links
• click tracking (analytics)
• link expiration

Non-Functional:

highly available (99.99%)

highly scalable (billions)

low latency (100 ms)

data durable (links shouldn't break)

security against abuse

Capacity estimation

Throughput

new url - 1K/second

URL redirects - 1M reqeusts/second

Bandwith

Average URL size - 2KB

Read bandwithc - 1M (minimal size) ~ 100 MB

Write bandwidth - 1K * 2 KB - 2 MB

Storage

1K/sec * 86400 = 86M/day

URL per year = 86 * 365 = 31B

Storage per URL - 1KB

5 year storage - 32B * 1KB* 5 = 155TB

API design

Define what APIs are expected from the system...

/getShortUrl(longUrl, alias, expiration) - shortUrl

/getLongUrl(shortUrl)

Analytics

/getUrlClicks(shortUrl, startDate, endData) - click count

Database design

URL mapping - no SQL database (fast key-value storage)

User Data - RDBMS

Analytics Data -t ime series dat a

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

62 bits - 7 chars - 62^7 - 3.5 trillion possibilities (a-z, A-z, -09)

bloom filter to check if it already exists

TTL for URL (expire) periodic clean up

Trade offs/Tech choices

Database reads during hig traffic

URL collisions

analytics processing with custom aclias

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?