What a real-time betting backend actually needs

Peer-to-peer betting looks like a socket problem from the outside. From the inside it's a correctness problem wearing a socket costume.

Three systems doing the real work

• A matching engine that decides which lay bet applies to which back bet, handling currency equivalence and brave-take rules without ever double-matching.
• A settlement job that runs on a schedule, computes each winner's proportional share of the net pool, and is idempotent so a retry never pays twice.
• A queue layer (BullMQ + Redis) that reconciles deposits and payouts, so a webhook arriving twice doesn't credit an account twice.

Get those three right and the sockets are almost incidental.