Design a Slack-like messaging system
Company: Crusoe
Role: Software Engineer
Category: System Design
Difficulty: medium
Interview Round: Technical Screen
Design a Slack-like messaging system that supports real-time messaging in channels and direct messages.
## Core features
- Users can send/receive messages in:
- Channels (public/private)
- Direct Messages (1:1) and small group DMs (optional)
- Real-time delivery to online users (web/mobile)
- Offline support (users can fetch history after reconnect)
## Non-functional requirements
- High availability and low latency for sending and receiving messages
- Ordering: messages in a channel should appear in a consistent order for users
- Scale: large number of concurrent connections and many active channels
- Durability: messages should not be lost once acknowledged
## What to cover
- APIs
- Data model and storage
- Real-time delivery mechanism
- Message ordering guarantees and trade-offs
- Scaling strategy (partitioning/sharding)
- Reliability, backpressure, and observability
Quick Answer: This question evaluates a candidate's ability to design scalable, highly available real-time messaging platforms, testing competencies in distributed systems, data modeling, real-time delivery, ordering guarantees, durability, and operational reliability.