Design a Voting System

Design a voting system. 100M users will be logging in within a window of 24h (not necessarily uniformly). Every user will be able to choose from a fixed list of options. If the user has already voted the system should not let them to vote a second time. Additional constraint: only the first 100K votes are accepted. If the quota is exceeded any attempt to vote should be rejected.

Authentication

• First of all, we need to find a way to authenticate our users, possibly in advance with an automated system connected to ID (social security, passport) to prevent fraud.

Voting

Since we can only allow 100k votes, and it would be a bad (but not terrible UX) to invalidate anyone who makes a vote after the 100k one. We can try to make this work by having a leader follower setup, with the leader writing ahead to the followers, and if a leader falls, having a new leader election.