Discord Engineering

Overview

Discord runs persistent, low-latency voice and chat for hundreds of millions of users organized into servers that can each hold a million-plus members, which is a workload pattern almost nobody else operates at. The blog is famous in three areas: a candid migration from Cassandra to ScyllaDB to store trillions of messages with predictable tail latency, gateway and WebSocket optimizations including the zstd-based compression rollout that cut traffic by roughly 40 percent, and the all-hands-on-deck work to make a single server handle a million concurrent users for one viral event. For interviews, 'How Discord Stores Trillions of Messages' is the canonical reference for chat-at-scale storage, and 'Pushing Discord's Limits with a Million+ Online Users in a Single Server' anchors fan-out and presence design questions.

Interview questions

• What can I learn from Discord's engineering blog?
• Which Discord posts are most useful for chat-storage interviews?
• Why is Discord's blog valuable for real-time fan-out design questions?

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