Our Pastebin service should meet the following requirements:

Functional Requirements:

Users should be able to upload or “paste” their data and get a unique URL to access it.
Users will only be able to upload text.
Data and links will expire after a specific timespan automatically; users should also be able to specify expiration time.
Users should optionally be able to pick a custom alias for their paste.
Non-Functional Requirements:

The system should be highly reliable, any data uploaded should not be lost.
The system should be highly available. This is required because if our service is down, users will not be able to access their Pastes.
Users should be able to access their Pastes in real-time with minimum latency.
Paste links should not be guessable (not predictable).