OpenShell/crates/openshell-driver-kubernetes

openshell-driver-kubernetes

Kubernetes-backed compute driver for OpenShell cluster deployments.

The driver uses the Kubernetes API to create, delete, fetch, and watch sandbox custom resources in the configured namespace. It runs in-process with the gateway server.

Runtime Model

The gateway stores platform state and delegates sandbox workload creation to this driver. Kubernetes owns scheduling and pod lifecycle. The openshell-sandbox supervisor inside each workload owns agent isolation, credential injection, policy polling, logs, and the gateway relay.

Sandbox Resource

The driver works with the agents.x-k8s.io Sandbox custom resource. It detects the served Sandbox API at runtime, caches the selected API version for the gateway process, and uses v1beta1 when available before falling back to v1alpha1. Restart the gateway after an in-place Agent Sandbox upgrade so the driver can detect served API versions again. Driver events map Kubernetes object state and platform events into the shared compute-driver protobuf surface used by the gateway.

Kubernetes API calls use explicit timeouts so gRPC handlers do not block indefinitely when the API server is slow or unavailable.

Workspace Persistence

Sandbox pods use a PVC-backed /sandbox workspace. An init container seeds the PVC from the image's original /sandbox contents on first start and writes a sentinel so subsequent starts skip the copy.

This is a stopgap persistence model. It preserves user files across pod rescheduling but duplicates the base workspace and does not automatically apply image updates to existing PVCs. Future snapshotting should replace it.

Credentials, TLS, and Relay

The driver injects gateway callback configuration, sandbox identity, TLS client material, and the supervisor SSH socket path into the workload. Driver-owned values must override image-provided environment variables.

Sandbox pods run as service_account_name and keep automountServiceAccountToken: false. The only Kubernetes token exposed to the supervisor is an explicit, audience-bound projected token mounted at /var/run/secrets/openshell/token for the one-shot IssueSandboxToken bootstrap exchange.

The gateway uses the supervisor relay for connect, exec, and file sync. Sandbox pods do not need direct external ingress for SSH.

Container Security Context

The default combined supervisor topology grants the sandbox agent container the Linux capabilities the supervisor needs for namespace setup and process, filesystem, and network policy enforcement.

The sidecar supervisor topology moves pod-level network setup into a root init container. In the default process/binary-aware mode, the long-lived network sidecar runs as UID 0 with allowPrivilegeEscalation: false, drops default Linux capabilities, and adds only SYS_PTRACE plus DAC_READ_SEARCH for cross-UID workload /proc inspection. The agent container also runs as the resolved sandbox UID/GID with allowPrivilegeEscalation: false and capabilities.drop: ["ALL"]. Set sidecar.process_binary_aware_network_policy = false to run the network sidecar as the configured non-root sidecar.proxy_uid, omit the extra /proc inspection capabilities, and enforce endpoint/L7 network policy without matching policy.binaries. In this mode OpenShell preserves gateway session and SSH behavior, but the process supervisor does not perform root-to-sandbox privilege dropping or supervisor identity mount isolation. It still applies Landlock filesystem policy and child seccomp filters where the kernel/runtime supports them. Network endpoint and L7 policy remain enforced by the network sidecar, and sidecar pods use a shared process namespace so the network sidecar can resolve process/binary identity through /proc/<entrypoint-pid>.

Sidecar mode keeps gateway credentials in the network sidecar. The agent container does not mount the projected service-account token used for sandbox token bootstrap, does not mount the sandbox client TLS secret, and does not get gateway callback environment variables. The process supervisor receives policy and provider environment state from the sidecar over a local control socket in the shared sidecar state volume. The sidecar accepts only the pre-workload process-supervisor connection, authenticates its UID/GID/PID with peer credentials, and removes the listener afterward. SSH relays use a Linux abstract socket whose peer PID must match that authenticated supervisor. Both supervisors exit if the control connection closes, coupling their container restart lifecycle before a new authoritative client can be established.

The driver can request a Kubernetes AppArmor profile through app_armor_profile.

Supported values are Unconfined, RuntimeDefault, and Localhost/<profile-name>. An empty or unset value omits securityContext.appArmorProfile. Helm deployments default sandbox agent containers to Unconfined because runtime/default AppArmor profiles can block the supervisor's network namespace mount setup on AppArmor-enabled nodes.

GPU Support

When a sandbox requests GPU support, the driver checks node allocatable capacity for nvidia.com/gpu and requests the configured GPU count in the workload spec. When no count is set, the driver requests one GPU resource. The sandbox image must provide the user-space libraries needed by the agent workload.

Driver Config

Following RFC 0006, this driver accepts the selected SandboxTemplate.driver_config.kubernetes block as DriverSandboxTemplate.driver_config. The Kubernetes driver owns the nested schema and currently accepts:

• pod.node_selector
• pod.tolerations
• pod.runtime_class_name
• pod.priority_class_name
• containers.agent.resources.requests
• containers.agent.resources.limits
• containers.agent.volume_mounts[].name
• containers.agent.volume_mounts[].mount_path
• containers.agent.volume_mounts[].sub_path
• containers.agent.volume_mounts[].read_only
• volumes[].name
• volumes[].persistent_volume_claim.claim_name
• volumes[].persistent_volume_claim.read_only

Nested keys inside the kubernetes block use snake_case. The top-level driver_config envelope is keyed by driver names, so kubernetes is not part of the nested schema.

Set this through the CLI with the public driver-keyed envelope. The gateway forwards only the kubernetes object to this driver:

openshell sandbox create \
  --driver-config-json '{"kubernetes":{"pod":{"runtime_class_name":"kata-containers","node_selector":{"pool":"gpu"}}}}' \
  -- claude

Resource keys use native Kubernetes resource names and quantity strings. The parser renders the keys listed above and rejects unknown fields. pod.runtime_class_name maps to PodSpec runtimeClassName and overrides the driver's configured default_runtime_class_name; the typed public SandboxTemplate.runtime_class_name still takes precedence when set. Use the public --gpu flag for the default GPU request, pass a count to --gpu for counted GPU requests, and use driver_config only for additional driver-owned resource details.

Use PVC volumes to mount existing Kubernetes PersistentVolumeClaims into the agent container. PVC volumes and mounts default to read-only unless read_only: false is set explicitly. Read-write access requires read_only: false on both the PVC volume and each writable mount. The driver rejects duplicate volume names, invalid DNS-1123 volume labels or PVC claim subdomain names, mounts that reference unknown volumes, non-normalized or protected mount paths, and absolute or parent-traversing sub_path values.

Any explicit driver-config mount under /sandbox disables the driver's default /sandbox workspace PVC injection for that sandbox. Only the explicit mount paths persist through the external PVC; other /sandbox paths come from the current sandbox image.

openshell sandbox create \
  --driver-config-json '{
    "kubernetes": {
      "volumes": [{
        "name": "user-data",
        "persistent_volume_claim": {
          "claim_name": "pvc-user-data-123",
          "read_only": false
        }
      }],
      "containers": {
        "agent": {
          "volume_mounts": [
            {
              "name": "user-data",
              "mount_path": "/sandbox/.openshell/workspace",
              "sub_path": "workspace",
              "read_only": false
            },
            {
              "name": "user-data",
              "mount_path": "/sandbox/.openshell/memory",
              "sub_path": "memory",
              "read_only": false
            }
          ]
        }
      }
    }
  }' \
  -- claude