Replit's New Sandbox Engine (Part 1): From Docker Containers to microVMs

Replit has completed a rewrite of its sandbox engine, changing the isolation boundary from shared-kernel Docker containers to microVMs based on KVM and Cloud Hypervisor. Each sandbox now has its own independent Linux kernel, and hundreds of millions of projects were migrated smoothly with no data loss. The new engine supports on-demand mounting of customer disks, memory snapshots, and cross-cloud deployment, and can orchestrate tens of thousands of microVMs simultaneously.