OpenShell/crates/openshell-supervisor

OpenShell supervisor

The supervisor loads and reconciles policy, maintains provider credentials, applies network and MCP inspection, and drives the admitted isolation backend through attachment, confirmation, and workload start.

Backend startup

The supervisor binary selects a backend setup and collects its launch inputs into a public SandboxInstanceConfig. Shared startup receives that config and the trusted backend setup separately. The backend_setup module owns that backend's launch-data decoder, workload policy discovery, and client construction. Descriptor contents cannot select an implementation.

Shared startup checks the admitted backend name before passing the opaque payload to its decoder. It then compares the decoded sandbox, session, and runtime generation with the trusted launch inputs before installing credentials or discovering workload policy. A mismatch stops startup.

The built-in decoder also carries the VM driver's fixed workload identity into shared policy validation. Startup and later policy updates must reject selectors that conflict with that identity. Other launch descriptors do not enable this VM-specific check.

The supervisor admits policy and prepares credentials before constructing and attaching the selected client. It uses the concrete RPC client handles BoundBoundary and ConfirmedBoundary from openshell-sandbox-backend: confirm the attached boundary, prepare network mediation, then start the workload. Backends supply native enforcement evidence through the Sandbox Protocol; the client validates it before exposing the confirmed handle.

The client receives the supervisor's live provider state, bearer-token slot, and CA-path slot. Provider refresh, token rotation, and later CA publication must remain visible through those shared handles. Startup does not create independent copies of their current values.

backend_setup, SandboxInstanceConfig, SandboxInstanceBindings, and run_sandbox_with_backend are public so the supervisor binary can select a registered backend. External backends should implement the IsolationBackend and SandboxProtocol services rather than link this crate.

The startup result separates the backend transport payload from optional authenticated CONNECT listener settings. Shared networking starts the listener only after boundary attachment and confirmation; the supervisor owns policy evaluation, live credentials, and listener lifetime. These settings do not add a proxy hook to the isolation interface or the shared Sandbox Protocol descriptor.

Sandbox instance ownership

A sandbox instance is one running generation of a stable Sandbox resource. Gateway connections, and the gateway supervisor sessions carried over them, can reconnect within an instance without creating another one; the generation remains the fencing identifier.

run_sandbox_instance supervises one sandbox instance from three inputs. SandboxInstanceConfig is the single launch configuration: identity, command, policy inputs, auth bundle, backend descriptor, and file locations. SandboxInstanceBindings is the live state its owner prepares once: the GatewayCredentials issued from the auth bundle, the OCSF context and JSON settings, the log sink, and the denial history served by policy.local. SandboxInstanceControls carries the owner's stop signal and readiness. Everything else, including credential renewal, policy, provider credentials and token grants, middleware credentials, the backend connection, and the access plane, is created by the instance. Gateway clients receive a GatewayEndpoint, which pairs the URL with that instance's GatewayCredentials; nothing is installed process-wide.

The dedicated process wrapper keeps the existing process contract. The binary loads the launch configuration from its arguments and environment and prepares SandboxInstanceBindings::dedicated, sharing one GatewayCredentials with log push and the OCSF JSON settings with its logging layers, so renewal by either gateway client keeps both current. run_sandbox_with_backend sets the process-wide OCSF context, binds the readiness socket and port to instance readiness, and stops the instance on SIGTERM or SIGINT.

sandbox_instance_host::SandboxInstanceHost runs several sandbox instances in one process. Each instance gets its own Tokio runtime; every thread of that runtime, and the thread driving it, is bound to the instance's SandboxInstanceBindings: OCSF context, OCSF JSON settings, log sink, and denial log. Spawned tasks, blocking work, callbacks, reconnects, and renewal therefore inherit the instance's identity, and threads outside an instance carry none and push no logs. The OCSF context also supplies the sandbox identity in middleware requests.

The host is the one registry of its instances. admit validates that the key is a single path component, then, under the registry lock, accepts the same launch fingerprint for an occupied key again, rejects a different one, and rejects any admission while the key is being removed. A new instance gets an empty private directory under the host root, and sandbox_instance_launch prepares its bindings and body there. A failed admission leaves no entry and no files.

Removing an instance stops its workload, shuts down only its runtime, which drops its runtime route, and revokes its gateway credentials; only then is its private directory deleted and its key released, so a replacement can never meet the old instance's resources. Removal runs on one detached task that every remover joins, so a caller that disconnects cannot cancel it, and it checks the entry's serial before releasing the key. If the directory cannot be deleted, the key stays reserved and reports a failed phase, and the next removal retries the deletion. An instance that panics reports a failure and is revoked the same way. An instance that is still starting is cancelled at once; the sandbox runtime then loses supervision and fails closed, as it does when a dedicated supervisor exits. A hosted instance without an explicit proxy trust directory uses its private directory. Hosted processes must install LogPushLayer::thread_bound and an OcsfShorthandLayer writing to SandboxInstanceDenialWriter.

Console logging

Diagnostics and OCSF shorthand share a bounded, nonblocking stderr writer. With ocsf_json_enabled=true, the same writer also receives timestamped OCSF-JSON records. Each formatter submits a complete line in one write so concurrent producers cannot interleave records in the queue. The 1,024-line queue drops new lines when full rather than waiting for stderr.

Console JSON is installed independently of optional file appenders and uses an INFO filter independent of the diagnostic filter. Its runtime enabled flag and target schema version are shared with the existing JSONL file layer. The supervisor retains the writer guards until shutdown. The gateway log push layer continues to emit shorthand only.

Safe runtime and parent liveness

The supervisor drives the safe isolation-backend contract and network/policy orchestration. Its library and executable forbid unsafe code.

For a VM host supervisor, the VM driver passes its parent-liveness pipe as stdin and sets the private --parent-liveness-stdin flag. A dedicated reader terminates the supervisor when the driver closes its write endpoint or exits. The driver protects both original pipe endpoints with close-on-exec and lets Stdio transfer the read endpoint to the child's stdin. The supervisor uses the standard stdin reader and does not adopt a numeric raw descriptor. This mode reserves stdin for liveness; sandbox workload input travels over the boundary protocol.

Portable supervisor access

The supervisor consumes the shared isolation backend contract. Its gateway session, canonical process attachment, and TCP readiness do not require SSH or a Unix host.

TCP readiness opens only after the gateway accepts the authenticated session. Session loss closes readiness; accepted reconnection restores it. Dropping the readiness guard closes the listener. A requested Unix readiness endpoint fails explicitly on unsupported hosts, even before session acceptance.

The optional Unix SSH adapter remains separate from boundary-based process I/O. The process-access multiplexer consumes boundary-provided streams and delegates terminal resizing and signals through the existing isolation contract. It does not own local PIDs, PTYs, or process-group signaling; native process operations belong to the sandbox or isolation backend. Signals use BoundarySignal.

These portable control-plane foundations do not qualify a platform isolation backend or enable a Windows workload runtime.

Shared supervisor host

openshell-supervisor --mode=shared --gateway-endpoint <https-gateway-url> --token-file <file> --address <ip:port> hosts the sandbox instances of many sandboxes in one process for the Kubernetes gateway supervisor topology. It is Unix-only. The host opens no control listener: it dials the gateway and receives its assignments from it.

• Gateway attachment. The host dials --gateway-endpoint (which must be https), verifying the gateway with OPENSHELL_TLS_CA and OPENSHELL_GATEWAY_TLS_SERVER_NAME like every sandbox instance does, and opens the private openshell.supervisor.host.v1/SupervisorHost.Attach stream (proto/supervisor_host.proto) with the supervisor token in --token-file as its bearer. The gateway mints that token with its launch-signing key under a profile of its own (typ openshell-supervisor+jwt, subject openshell-supervisor:<gateway_id>, no sandbox, generation, or epoch claims) and keeps the file fresh through its deployment packaging (the Helm chart's <release>-supervisor-token Secret). The token authorizes nothing but this stream; sandbox, extension, user, operator, and peer credentials are refused on it. The host re-reads the file on every connection attempt and treats a missing, malformed, or expired token as a reason to retry later, and the gateway ends a stream when the token that opened it expires, so the host reconnects with the renewed one. The host never acts with any other identity and has no Kubernetes identity. The stream starts with a hello carrying a per-process instance id and a connection epoch; the gateway supersedes an older stream of the same process and refuses a delayed older connection.
• Assignments. The gateway owns the desired set and sends it as complete AssignmentSnapshots with session-scoped revisions. shared_host::SharedHost::reconcile validates the snapshot as a whole (at most 256 instances, no route twice), decodes each assignment's launch material (the JSON SandboxInstanceRegistration of openshell-supervisor-control), admits it into the SandboxInstanceHost registry keyed by route with the registration digest as its fingerprint, and removes every hosted route the snapshot omits. An identical assignment is a no-op; one that cannot be admitted (invalid material, or a different fingerprint for a live route) is reported as a failed instance and never touches the running one. Snapshots are reconciled one at a time on a separate task, so heartbeats and status keep flowing while instances stop; only the newest unapplied snapshot is kept, and a connection finishes the reconciliation it started before the next connection begins. Private files live under --session-root (proxy CA, trust directory, SSH socket); the registry owns removal and keeps the route reserved until the instance has ended and its files are deleted.
• Status. After each reconciliation and whenever an instance is admitted, changes phase or readiness, or is removed, the host sends a complete HostStatus naming the revision it has reconciled to; readiness is set only once the gateway has accepted the instance's own supervisor session.
• Disconnects. Losing the gateway stream never stops an instance. The host reconnects with backoff, reports what it runs, and applies the first snapshot of the new session; only a snapshot that omits an instance, or process shutdown, stops it.
• Runtime connections. One routed listener (--runtime-listen) accepts every instance's runtime-initiated Sandbox Protocol connections; see openshell-sandbox-backend for the routing preface.
• Health. --address is a plain TCP listener that accepts and closes kubelet tcpSocket probe connections; it carries no control traffic and reports only that the process runs. SIGTERM and SIGINT stop every instance, which ends their workloads' supervision.

Sandbox instances get no upstream proxy, extra CA bundle, or provider workload identity: the Kubernetes driver refuses the topology when an upstream proxy or provider SPIFFE identity is configured, so a workload never silently loses them. The host also initializes no OTLP trace or OCSF exporters, because one process cannot export each instance's records with that instance's collector headers and identity. Its console logs and each instance's gateway log push remain, and the Kubernetes driver warns at startup when the gateway configures supervisor export.