OpenShell/crates/openshell-driver-docker

openshell-driver-docker

Docker-backed compute driver for local and remote OpenShell gateways.

The driver uses bollard to manage sandbox resources through the configured Docker API socket. When socket_path is unset, it selects the first standard local socket that responds to an API ping. An explicitly selected Docker driver falls back to /var/run/docker.sock when no candidate responds.

When the gateway configures [openshell.gateway.otlp], the in-process driver exports spans to the same OTLP/gRPC collector as openshell-driver-docker. The standalone driver accepts OPENSHELL_OTLP_ENDPOINT, continues W3C trace context from gateway RPC metadata, and flushes spans during graceful shutdown.

Runtime Model

The driver creates two containers for each sandbox:

• openshell-sandbox is PID 1 in the workload container. It owns the workload process tree, seccomp notification broker, mandatory Landlock baseline, binary identity, exec/signal/wait/PTY operations, and loopback forwarding.
• openshell-supervisor runs in a separate companion container. It owns the gateway session, policy engine, credentials, interception CA, SSH relay, L7 inspection, DNS policy, and external upstream connections.

Both containers are non-root, request no capabilities, and set no-new-privileges. A shared named volume carries the authenticated Unix socket and sandbox bootstrap material. A second supervisor-only volume carries the supervisor JWT and gateway client credentials and is never mounted into the workload.

The workload uses network_mode=none. Its seccomp user-notification broker mediates every supported TCP and DNS operation, attributes it to the calling binary, and sends the request across the private channel. The supervisor authorizes the request before it opens an upstream connection. Docker's absent workload network is the mandatory outer fence if mediation fails or is bypassed. The trusted supervisor companion uses Docker host networking, where it reaches the gateway's primary loopback listener and originates approved egress.

The driver copies trusted runtime bytes from the configured supervisor image through the Docker archive API. No workload launch depends on a host bind mount or a tool supplied by the workload image, so the same path works with local, remote, and VM-backed Docker daemons.

Identity and Workspace

Before creating the workload, the driver pins the image ID and reads its passwd/group databases through a stopped metadata container. It resolves the admitted policy identity, or the image Config.User fallback, into one exact non-root UID, primary GID, and supplementary-group set. Docker launches openshell-sandbox with that identity, and the sandbox uses the same identity for every canonical and exec process. UID or GID zero and unresolved symbolic identities are rejected.

An absolute OCI working directory becomes the workspace. An empty, root (/), or explicit /sandbox declaration uses /sandbox. Any other workdir must already exist without symlink components. The resolved identity must be able to traverse every parent and write and enter the workdir; OpenShell does not change its ownership or mode.

Image VOLUME declarations and user mounts must not cover the workdir, one of its parents, or the reserved /.openshell runtime/channel tree. OpenShell asks the kernel to validate access under the final identity, so POSIX ACL and host LSM decisions remain authoritative.

Container Contract

Setting	Purpose
Exact non-root user and group_add	Gives sandbox and workload the same immutable UID/GID/group identity required for capability-free observation.
cap_drop = ALL, no cap_add, no-new-privileges	Prevents either container from acquiring Linux capabilities.
Docker default seccomp and AppArmor profiles	Retains runtime hardening; startup confirmation fails closed if nested seccomp notification is unavailable.
network_mode = none on the workload	Removes direct external routes.
network_mode = host on the supervisor	Lets the trusted supervisor reach the gateway's primary loopback listener and originate approved upstream connections.
restart_policy = no	Keeps canonical main-process exit terminal.
PidsLimit	Applies the configured sandbox PID budget. Omit sandbox_pids_limit to use OpenShell's default. Explicit zero is invalid.
Private named volumes	One carries the authenticated sandbox/supervisor channel. The other is mounted only into the supervisor and contains its JWT and private gateway credentials.
In-memory /run/openshell-supervisor-ca tmpfs	Holds only the public supervisor CA certificate and trust bundle without making all of /run writable.
CDI GPU request	Assigns the exact validated CDI devices requested by driver config or count-based selection.

Stop, Start, and Delete

Stop terminates the supervisor companion and stops the workload container without removing it. Docker retains the workload writable layer and attached volumes. Start stages a fresh sandbox bootstrap bundle, restarts that workload, and creates a new supervisor companion. A durably stopped sandbox stays stopped across gateway restarts.

Delete force-removes both containers, the driver-owned runtime volumes, and the host-private runtime descriptor. Missing or altered descriptor and channel resources fail closed; the driver does not run an older combined-supervisor layout.

Driver Config Mounts

The gateway forwards the docker block from --driver-config-json. Supported mount types are:

• bind: an absolute daemon-host path, allowed only when [openshell.drivers.docker].enable_bind_mounts = true.
• volume: an existing named volume. The driver never creates or removes a user-supplied volume. Bind-backed local volumes require enable_bind_mounts = true.
• tmpfs: an in-memory filesystem with optional size and mode.

Host bind mounts are disabled by default because they expose daemon-host paths to sandbox requests. User bind and volume mounts are read-only by default. Targets must be absolute, normalized paths and cannot overlap the workspace root or OpenShell control paths.

Example:

docker volume create openshell-work

openshell sandbox create \
  --driver-config-json '{"docker":{"mounts":[{"type":"volume","source":"openshell-work","target":"/sandbox/work"}]}}' \
  -- claude

Runtime Image

sandbox_runtime_image contains the statically linked musl /openshell-sandbox binary. The driver extracts that binary as bytes and stages it into the stopped workload. supervisor_image contains the dynamically linked glibc /openshell-supervisor binary that runs in the host-networked supervisor container. Release and gateway image builds bake matching image tags into the binary.

Gateway session and TLS

OPENSHELL_ENDPOINT and gateway authentication material are injected only into the supervisor companion. The workload never receives the sandbox JWT, gateway client TLS key, policy authority, or interception CA private key.

When no endpoint is configured, the supervisor connects to 127.0.0.1:<gateway-port>. Set grpc_endpoint when the gateway is not on the Docker daemon host. A configured HTTPS server certificate must include the endpoint host in its subject alternative names.

The driver publishes host loopback as the backend address for host.openshell.internal. Policy DNS resolves that reserved name through the mediated path, so policies can reach host services without a Docker bridge, container DNS alias, or another gateway listener.

Docker Engine on Linux supports host networking directly. Docker Desktop requires host networking to be enabled in Settings and does not support it when Enhanced Container Isolation is enabled.

The supervisor owns these security-critical variables:

• OPENSHELL_ENDPOINT
• OPENSHELL_SANDBOX_ID
• OPENSHELL_SANDBOX
• OPENSHELL_SANDBOX_TOKEN_FILE
• OPENSHELL_SSH_SOCKET_PATH
• OPENSHELL_MAIN_PROCESS_SPEC
• TLS path variables when HTTPS is enabled

Template and sandbox environment is encoded in the protected bootstrap and exposed only to workload children. Workload input cannot override security-critical supervisor variables.