Dinner Plans & Distributed Systems : A Fun Guide to Consensus

#beginners #computerscience #systemdesign #interview

Picture this: a group of friends is starving and trying to decide where to eat. What seems like a simple dinner plan is actually a perfect way to explain how computers in a distributed system agree on things. Let’s turn these friends into servers and see how three big consensus algorithms—Paxos, Raft, and BFT—play out in real life.

Paxos: The Democracy (But a Messy One)

Friend A says, “Let’s get pizza!” They’re the proposer. The rest of the group listens and becomes acceptors—they raise hands if they like the idea. If most agree, boom—pizza it is! The learners are the ones who didn’t vote but need to know the final plan so they don’t show up at the wrong place. Paxos works even if some friends leave the chat, but if too many people propose at once (“No, tacos!” … “Burgers!”), chaos happens. That’s why sometimes one friend is chosen to always suggest options—smoother but still a bit complicated.

Raft: The Leader Everyone Follows

This time, the group elects a leader—let’s say Friend B. Friend B declares, “We’re having sushi tonight.” Everyone nods and follows along. If Friend B suddenly drops out (maybe their phone dies), the group quickly votes for a new leader and continues. Raft makes the process simple: one person decides, everyone else follows. No endless debates, just clear direction.

Byzantine Fault Tolerance (BFT): Handling the Trickster

Now imagine Friend C is a prankster. They whisper to some, “We’re going for burgers”, while telling others, “It’s definitely pizza.” Uh oh—chaos! To deal with this, the group double-checks plans with multiple friends before trusting anything. It takes more talking and time, but ensures that no one gets fooled. That’s BFT: built for situations where not everyone is trustworthy—perfect for blockchains, where some participants might try to cheat.