System requirements

Functional:

1. User Registration and Authentication.
2. Short URL Generation.
3. User Limits.
4. URL Expiration.
5. Redirection.
6. Analytics Tracking.
7. Error Handling.
8. Performance.
9. Monitoring and Alerting.

Non-Functional:

1. Scalability: The system should handle increased traffic seamlessly.
2. Availability: The service should have an uptime of 99.9% or higher.
3. Performance: Response to redirection requests should be within 100ms under normal load, and support up to 10,000 requests per second during peak traffic.
4. Security: User data must be stored securely, employing encryption and protections against vulnerabilities.
5. Data Integrity: Consistency in the mapping between short and long URLs must be maintained.
6. Usability: The user interface should be intuitive and provide clear feedback to users.
7. Maintainability: The codebase should be well-documented and adhere to best practices.
8. Logging and Auditability: All user actions and significant events should be logged for auditing.
9. Load Balancing: The architecture should support load balancing across multiple servers.
10. Backup and Recovery: Regular backups should be performed, and a disaster recovery plan must be established.

Capacity estimation

Assume we want every URL to be 7 alphanumeric digits. Url can consist of 26 letters and 10 numbers, giving 36 possible characters. 36^7 = 78 364 164 096. The total possible number of combinations 78 billion unique URL.

Datadabase size :

Short URL table will contain :

• unique Id (4bytes)
• short URL (7 bytes)
• access count (4 bytes)

Therefore each record would require approx : 7+4+4 bytes = 15 bytes

78 billion record multiplied by 15bytes = 1097GB

API design

• Sign up
• Login
• Sign out
• Url creator

Database design

Defining the system data model early on will clarify how data will flow among different components of the system. Also you could draw an ER diagram using the diagramming tool to enhance your design...

High-level design

We need APIs for signup, login, URL converter. We need DB to cache most common URL redirect and to store longurl and short URL. We would need a load balancer to distribute the traffic and some monitoring and analytics in place. The URL convertor logic will use MD5

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?