Design Presence at Scale

Presence is a payload that rides the same real-time gateway that already delivers messages, so reuse the gateway's fan-out instead of reinventing it. Every Discord client already holds one persistent WebSocket to the gateway. A session process on the BEAM virtual machine represents the connection, and a guild process represents each server. Messages fan out through that fabric, and presence takes the exact same path. A status change is published to the connected sessions that should see it, using the same relays that already cut work for large servers. A candidate who designs a separate presence service with its own connections has doubled the hardest part of Discord's architecture. Say early that presence is coupled to the gateway and reuses its session, guild, and relay machinery, and you have shown you understand how the pieces fit rather than reciting a status-table CRUD design.