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Runtime Selection Guide: Kata vs gVisor vs WebAssembly

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Context

We run ephemeral, agentic workloads (CLI coding agents, MCP servers, short-lived containers that produce artifacts and exit). We care about isolation, startup latency, and cost.

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WebAssembly (Wasm)

  • Runs code in a lightweight, stack-based virtual machine, not a full OS container.
  • Fastest startup (milliseconds).
  • Highest density (thousands of sandboxes per node).
  • Requires applications to be compiled to .wasm (WASI) or use a Wasm-compiled interpreter (e.g., Python/JS in Wasm).
  • Best for: Pure compute tasks, language-specific snippets, serverless-style functions.
  • Tradeoff: Limited system access (WASI only, no full Linux kernel/syscalls), requires specialized build artifacts.

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gVisor

  • User-space kernel (“Sentry”) intercepts syscalls.
  • Containers do not talk directly to the host kernel.
  • Fast startup, low memory overhead.
  • Feels like Linux (bash, FS, compilers work well).
  • Some syscalls are emulated or restricted.
  • Tradeoff: Strong sandbox, but technically shares the host kernel (via interception). Optimized for general-purpose compatibility.

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Kata Containers

  • Containers run inside lightweight VMs (hardware virtualization).
  • Strongest isolation (VM boundary, no shared kernel).
  • Higher startup latency and resource overhead.
  • Best for untrusted customer code, regulated workloads, or strict multi-tenancy.
  • Tradeoff: Maximum security, lower velocity, and higher cost.

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Recommendation

1. Use WebAssembly (Wasm) for:
  • Ultra-short-lived tasks (< 1s execution).
  • Pure logic/compute functions (e.g., “Verify this JSON schema”, “Calculate this fibonacci”).
  • Massive scale where startup time dominates total duration.
2. Use gVisor (Default) for:
  • Standard CLI coding agents (Claude Code, Codex).
  • Workloads needing standard Linux tools (git, curl, grep, npm).
  • MCP-connected toolchains.
  • “Do work -> write files -> exit” workflows.
3. Use Kata Containers for:
  • High-risk, untrusted customer-supplied binaries.
  • Workloads requiring root privileges that might escape a container.
  • Compliance-heavy environments requiring VM isolation.

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Proposed Model

  • Ultra-Fast / Compute: WebAssembly (WasmEdge/Spin)
  • General Purpose / Agentic: gVisor (runsc)
  • High Security: Kata Containers (kata-qemu/kata-fc)

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Outcome

  • Tiered runtime strategy balancing speed, compatibility, and security.
  • massive scale for simple tasks (Wasm).
  • Developer-friendly compatibility for agents (gVisor).
  • Hardened security for high-risk zones (Kata).