Beyond Kubernetes at Modal: How to Scale 1 Million Concurrent Sandboxes in Seconds

Good writeup on what breaks when you push Kubernetes past its design point: etcd, plus one serialized scheduler. Modal replaced both - each worker is its own source of truth, and a fleet of scheduling servers talks to them over RPC. Result: 1 million concurrent sandboxes in under a minute, 50,000 creations a second, median startup-to-code under 0.5s. Their rule travels well: anything O(nodes) scales horizontally or not at all.