Modal rebuilds sandbox infra: 1 million concurrent sandboxes in under a minute

Modal engineers described replacing Kubernetes-based orchestration to scale sandboxes: workers became the source of truth and scheduling was parallelized instead of relying on etcd. A benchmark created 1 million sandboxes in under a minute, with median startup-to-code time under 0.5 seconds.

• 1 million sandboxes created in under a minute in benchmark
• Median startup-to-code time under 0.5 seconds
• Workers publish state to a single Redis stream, viable past 100,000 workers
• Scheduling is parallelized; workers accept or reject requests directly