Design Slack — OpenAI — Intervues

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[ INFO ] category: System Design  difficulty: hard  freq: high  first seen: 2026-01-13
[HARD][SYSTEM DESIGN][HIGH]webbackendScalabilitySystem DesignmobileReal-timeMessagingWebSocketinfrastructure
$ cat problem.md
Design a Slack-like chat system supporting direct messages and group channels.
Requirements:
Send messages to groups or individuals
Create group chats, add/remove users
Push notifications for new messages
Unread message indicators
Rich media support (images, files)
Message deletion
Search functionality
Key Components:
Message Service
Channel Service
Notification Service (WebSocket/SSE)
Search Service (Elasticsearch)
Media Storage (S3)
Presence Service
Discussion Points:
Fan-out on write vs read for large channels
Multi-tenant architecture
Global deployment with data locality
Handling stuck running states with reconciler
Message ordering guarantees
user@intervues:~/openai$ 