Katkat
Back

Design a TCP Discord-like chat server

DiscordSoftware Engineer · Onsite
MediumSoftware EngineerOnsiteSystem Design

Last updated

This question evaluates a candidate's skills in system design, TCP-based protocol design, real-time messaging, data modeling, persistence, session/reconnection handling, and concurrency control for backend services.

Design a Discord-like chat server that accepts multiple clients over raw TCP (e.g., test via PuTTY/telnet).

Functional requirements:

  • Clients connect over TCP and can send line-based messages.
  • Support slash commands:
  • /help show available commands
  • /nick <name> set/change nickname
  • /users list users (at least in current room, or globally—state your choice)
  • /quit disconnect
  • Chat rooms:
  • Create rooms, join rooms, and list rooms
  • Messages sent to a room are broadcast to all users currently in that room
  • Reconnection:
  • If a client disconnects and later reconnects (identify how), they should be able to rejoin their previous rooms
  • Message history:
  • When a user joins a room, show the last 10 messages from that room
  • Persistence:
  • Data must persist across server restarts (users/rooms/membership/messages as needed)

Non-functional requirements:

  • Keep scalability in mind (multiple concurrent clients; discuss how to scale beyond one process/host).

Explain your protocol, core data model, key components, and how you would handle concurrency, durability, and scaling.