Half a million open connections, no surprises.

The self-managed gateway had been a clever piece of engineering when the platform was small. At scale, the operational model didn’t scale with it — connection state was in-process, broadcasts required cross-instance messaging the team had built by hand, and fault tolerance was "if the box dies, all clients reconnect at once."

API Gateway WebSocket API moved connection management to a managed service. Connection state moved to DynamoDB so any Lambda invocation could find the right route key. Broadcasts fanned out via SQS to keep the broadcaster latency-insensitive to subscriber count.

Peak concurrent connections hit 520k during a viral event without alerting on anything. Connection-drop rate stayed under 0.05% per hour. Operational hours dropped 94% — there’s no more "WebSocket gateway on-call." p99 message latency stays under 90ms steady-state.