Replit Replaces Docker with MicroVMs for AI Agent Sandboxing

• Replit migrated its sandbox engine from Docker to microVMs, completing a zero-downtime transition for hundreds of millions of projects.
• The new architecture uses Cloud Hypervisor and KVM to provide hardware virtualization isolation, addressing security gaps exposed by autonomous AI agents.
• Sandbox acquisition time is approximately 500 ms, including volume attachment and parallel service configuration.
• The minimal guest kernel avoids 96.1% of 6,211 Linux-CNA CVEs published between June 1 and November 4, 2026.

Security and Isolation

• MicroVMs prevent host kernel compromise even if the guest kernel is breached, unlike shared-kernel containers.
• eBPF and Linux Security Modules (LSM) monitor runtime behavior, with security component updates hot-reloaded to all sandboxes within 15 minutes.
• Network isolation uses Linux VRF and host-side egress proxies to enforce TLS hostname verification and block unauthorized traffic.

Infrastructure and Performance

• A remote block-storage service (vhost-user virtio-blk) enables on-demand data fetching and copy-on-write disk forking.
• Bring Your Own Cloud (BYOC) support allows customers to run workloads on AWS, Google Cloud, and Azure.
• The system supports general-purpose Linux VMs for internal Replit operations, including incident investigation and code review.