Design a Slack-like chat system
Company: Discord
Role: Software Engineer
Category: System Design
Difficulty: medium
Interview Round: Onsite
## System Design: Slack-like Messaging (Channels + DMs)
Design a Slack-like messaging backend that supports:
- Public/private **channels** with many members
- 1:1 and small group **direct messages**
- Sending and receiving messages with low latency
- Message history (scrollback)
Interview focus areas (expect deep follow-ups):
- **Data model** for channels, membership, messages
- **Fanout strategy** (write fanout vs read fanout)
- **Indexing / querying** for message history and (optional) search
- **Database choice** and sharding/partitioning
- Ordering guarantees and handling edits/deletes
- Hot channels and performance bottlenecks
State your assumptions (scale, retention, consistency needs) and propose an end-to-end architecture.
Quick Answer: This question evaluates system-design competencies such as data modeling for channels and direct messages, scalability and sharding, fanout and delivery strategies, consistency and ordering guarantees, indexing and query patterns for message history, and low-latency architecture for real-time messaging, and it belongs to the System Design domain.