Requirements

Functional Requirements:

• Create a short URL for a given long URL.
• Return the long URL associated with a given short URL.

Non-Functional Requirements:

Let's assume we have

• 1b of the long url usage over 90 days.
• After 90days, we should delete the urls which are never visited again.
• qps can be 1M/s ppk
• We have multiple geo locations globally.

API Design

The basic function can just use 2 apis:

1. Post getShortUrl(String longUrl) : string ShortUrl. the api will be used to generate a short url and return a short url
2. Get getLongUrl(String short) : string longUrl. This api is used to look up a long url per shortUrl
3. Get short url redirect to long url

High-Level Design

1. We are going to have 6 components: client, CND, server, database and a worker to clean the data which created over 90days and never visited again.
2. The create api with long url come to server, server reads from cache, if cache doesnt have one, read from db, if db also doesn't have the short url. Then we generate the short url in the server, then write to cache and db and then respond to cdn and store in the cdn cache.
3. The get api can live in the cdn.
4. cdn has a ttl 7 days.
5. For generate we can use Base62[0-9A-Za-z] with 8 characters to generate a short url.

Detailed Component Design

database store (kv):

1. The key is long url and value is short url.
2. has meta data is expire_at
3. Set a ttl, when 90days arrive clean the data.

worker listen to cdn log:

1. if a url has access log, update the data entry's expire_at in the db