Our URL shortener system should meet the specific requirements.

The following are functional requirements:

• Given an URL, our service should generate a shorter and unique alias of it
• When users access a shorter URL, our service should redirect them to the original link

The following are non-functional requirements:

• The system should be highly available. This is required because, if our service is down, all the URL redirections will start failing.
• URL redirection should happen in real-time with minimum latency.
• Shortened links should not be guessable (or predictable).

The following are extended requirements:

• Analytics, for example, how many times a redirection happened?
• Our service should also be accessible through REST APIs by other services

Let's calculate the size of the database and bandwidth required by the system to go live.