Real-time delivery is usually where "free tier" architecture stops working. The moment you need sub-second delivery across many concurrent conversations, most people reach for a dedicated WebSocket server — and a bill that comes with it.
Here's a different approach, used to build and run a real-time group chat app in 5 days on $0/month infrastructure at its current scale.
The core problem
Real-time chat needs two things that don't naturally coexist on a shared, single-tenant server: isolation (one busy conversation shouldn't slow down every other conversation) and low, predictable latency at the edge, close to wherever the user actually is.
The approach: isolate, then shard
