Design a URL Shortening Service like Bitly

Functional Requirements:

• Given a long URL, generate a unique, shortened URL.
• Given a shortened URL, redirect to the original long URL.
• (Optional, if time permits) Allow users to specify a custom short URL alias.

Non-Functional Requirements:

• High availability: The service should be available at all times, especially for redirection requests.
• Low latency: Redirection from short URL to long URL should be fast (e.g., <10ms).
• Scalability: The system should handle increasing numbers of requests and data growth over time.
• Consistency: Once a short URL is created, it should reliably map to the same long URL.
• Durability: Mappings should not be lost once created.
• Security: Prevent abuse (e.g., rate limiting, spam detection).