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App Studio Sandbox Runtime

App Studio owns the live development runtime API for projects. It keeps the Project-level capability contract, the file workspace, sync/restart/log/status operations, signed preview URLs, and preview proxying in the App Studio backend.

Infrastructure owns the resource composition. The sandbox-runner Template creates a SandboxRunner API through KRO and materializes the runtime namespace, PVC, Deployment, Service, control Secret, and network policy.

The first runtime implementation is intentionally small:

  • one infrastructure-backed SandboxRunner resource per App Studio Project
  • one Kubernetes namespace per runner
  • one PVC, Deployment, and Service per runner
  • one runner HTTP service in the pod for sync, restart, logs, and preview

For local Tilt development, sandbox-runner-image builds and loads the default runtime image with:

make load-sandbox-runner-image

Current Security Caveats

This POC runs user-generated code in a Kubernetes pod and should be treated as a development-only runtime. It does not yet provide a complete untrusted-code sandbox.

Known limitations:

  • no AppArmor or runtime-class hardening is configured
  • runner images are not defaulted by App Studio; configure immutable digest references before creating SandboxRunner resources
  • file sync is text-file oriented and skips binary or oversized App Studio files

Before promoting this beyond local/dev use, add explicit runtime isolation, quota defaults, image provenance controls, and network policy hardening.

Runtime kubeconfig RBAC

APP_STUDIO_RUNTIME_KUBECONFIG must be scoped to only the runtime data-plane operations App Studio performs after validating deterministic SandboxRunner refs. The credential should not be cluster-admin. A minimal role needs:

rules:
  - apiGroups: [""]
    resources: ["secrets", "endpoints"]
    verbs: ["get"]
  - apiGroups: [""]
    resources: ["services/proxy"]
    verbs: ["get", "create"]
  - apiGroups: [""]
    resources: ["namespaces"]
    verbs: ["delete"]

Capability Boundary

App Studio should only depend on these runtime capabilities:

  • sync
  • restart
  • logs
  • status
  • signed project preview proxy

Infrastructure should only publish deterministic runtime refs for the SandboxRunner: namespace, preview Service, control Service, and control Secret. App Studio validates those refs against the runner name before using the runtime kubeconfig, so forged status cannot redirect control-plane credentials to arbitrary Services or Secrets.