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name: virtualization description: | Virtualization and isolation architecture: hypervisors (type-1/type-2), container internals (namespaces, cgroups), microVMs, and the isolation-vs-overhead spectrum. Architect-level choice of isolation boundary.

USE WHEN: choosing an isolation/virtualization boundary, "hypervisor", "KVM", "type-1/type-2", "container", "namespaces", "cgroups", "microVM", "Firecracker", "gVisor", "Kata", multi-tenant isolation, sandboxing untrusted workloads.

DO NOT USE FOR: Kubernetes/Docker operational config (use infrastructure skills); OS internals (use os-kernel-architecture). allowed-tools: Read, Grep, Glob

Virtualization & Isolation

The isolation ↔ overhead spectrum (pick the weakest sufficient boundary)

Boundary	Isolation	Overhead / density	Boot	Fits
Process + namespaces/cgroups (containers)	Shared kernel → weakest	Lowest, highest density	ms	Trusted multi-service
gVisor / user-space kernel	Syscall interception	Moderate; some perf loss	ms	Semi-trusted, k8s-friendly
microVM (Firecracker, Kata)	Own kernel, tiny device model	Low-ish; ~125ms boot	fast	Untrusted multi-tenant (FaaS)
Full VM (type-1 KVM/Xen, type-2)	Strong, own kernel + devices	Highest per-VM	s	Strong tenant isolation, mixed OS

Decision driver: trust level of the workload. Untrusted/multi-tenant code → at least a microVM; trusted internal services → containers.

Mechanics worth pinning down

• Type-1 (bare-metal: KVM, Xen, Hyper-V, ESXi) vs type-2 (hosted: VirtualBox). Hardware-assisted virt (VT-x/AMD-V, EPT/NPT) is assumed.
• Containers = namespaces (pid/net/mnt/user/…) + cgroups (CPU/mem/io limits)
  • capabilities + seccomp + (often) a userns for rootless. NOT a security boundary against kernel exploits by themselves.
• microVMs: minimal device model + own guest kernel → VM-grade isolation at near-container speed/density; the FaaS sweet spot (Lambda uses Firecracker).
• Confidential computing: SEV-SNP/TDX encrypt guest memory from the host — for untrusted-host scenarios (pairs with security architecture).

When to recommend what

• Internal trusted microservices → containers + cgroups, seccomp, rootless.
• Run untrusted/tenant code → Firecracker/Kata microVMs or gVisor.
• Mixed OS / strong tenant separation / legacy → full VMs on type-1.