[System Design Tech Case Study Pulse #17] How Discord's Real-Time Chat Scales to 200+ Million Users

With detailed explanation and flow chart....

Oct 21, 2025

∙ Paid

Hi All,

Apache Cassandra plays a crucial role in scaling Discord’s real-time chat platform to serve over 250 million users. This impressive feat enables Discord to provide low-latency, highly available messaging across millions of servers and channels.

Let me dive deep into how Discord engineered this system, exploring the key architectural decisions, scaling strategies, and optimizations that enable Cassandra to manage this enormous volume of real-time chat data for Discord's global user base.

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System Overview

- Active users: 250 million+
- Concurrent users: 15 million+
- Messages sent daily: 4 billion+
- Servers (communities): 19 million+
- Peak messages per second: 4 million+
- Data centers: Multiple, globally distributed
- Latency target: < 100 milliseconds
- Availability: 99.99%+
- Supported platforms: Web, desktop, mobile
- Cassandra clusters: Multiple, purpose-specific