Firecracker MicroVM Sandbox Decision Framework: ~125ms Boot, <5MiB Overhead for Untrusted Agent Code vs gVisor 10-30% I/O Overhead for Compute-Heavy Workloads

Northflank·medium signal

Northflank published a comprehensive sandbox decision framework for AI agents executing untrusted code. Three tiers: Firecracker microVMs (~125ms boot, <5MiB memory, dedicated kernel per workload) for strongest isolation; gVisor (user-space kernel, syscall interception, 10-30% I/O overhead but minimal compute overhead) for trusted-but-sandboxed workloads; hardened containers only for fully trusted code. Production recommendation: default to microVMs for untrusted code and relax only when threat model justifies it. Defense-in-depth requires combining isolation boundaries, resource limits, network controls, permission scoping, and monitoring.