Steps:
    1.
Requirements clarifications

        1.
URL is too long to remember, tiny URL will have ability to redirect to long URL from short URL
        2.
Give a long URL, encode to a shorted URL and return
        3.
Give a short URL, return the original long URL
        4.
User should be able to pick a custom short URL
        5.
Should have a expiration time.
    2.
API Design

        1.
String encode(String longUrl, timestamp)
        2.
String decode(String shortUrl)
        3.
String encode(String longUrl, String shortUrl)
        4.
String renew(shortUrl, timestamp)
    3.
Volum scale Estimation

        1.
The avalibilty should be 100%, once service is down, user will not able to access the link.
        2.
Read heavy, read vs write 100 : 1
        3.
Assume 10M per day, 10B per day read, 100 URL /s, 10K / s read
        4.
Assume we keep data for 5 years, 10M * 365 * 5 = 20B
        5.
Assume 1 data is 1 kb, 20 TB store
        6.
Bandwidth: 100 M
    4.
Defining Data model

        1.
URL

            1.
shortUrl
            2.
longUrl
            3.
createTime
            4.
expTime
            5.
userId
        2.
User

            1.
userId
            2.
userName
            3.
lastLogin
    5.
High-level (Draw component)

        1.
Encode- decode- storing
    6.
Core component detail (load balancing, data set replica).

        1.
Base64Hash + sequence number
        2.
Generate random UUID
    7.
Bottlenecks,transparence, alert.

        1.
DB clean up, Cache, Load Balancer,