# openshell-driver-docker

Docker-backed compute driver for local OpenShell gateways.

The driver manages sandbox containers through the local Docker daemon with the
`bollard` client. It is intended for developer environments where Docker is
already available and running Kubernetes would be unnecessary.

The driver connects to `[openshell.drivers.docker].socket_path` when configured.
Otherwise, it uses the first standard local Docker socket that responds to an
API ping, which is the same selection mechanism used by gateway auto-detection.
An explicitly selected Docker driver falls back to `/var/run/docker.sock` when
no candidate responds.

## Runtime Model

The gateway runs as a host process. The Docker driver creates one container per
sandbox and starts the `openshell-sandbox` supervisor inside that container. The
supervisor then creates the nested sandbox namespace for the agent process.

Docker containers join an OpenShell-managed bridge network. The driver injects
`host.openshell.internal` and `host.docker.internal` so supervisors have stable
names for reaching the gateway host. On Docker Desktop, Colima, Rancher
Desktop, OrbStack, and macOS-hosted gateways, those names use Docker's
`host-gateway` alias. On native Linux Docker, the gateway also binds the bridge
gateway IP so containers can call back to the host process.

## Container Contract

The driver-controlled container settings are part of the sandbox security
contract:

| Setting | Purpose |
|---|---|
| `user = "0"` | The supervisor needs root inside the container to prepare namespaces, mounts, Landlock, and seccomp. |
| `network_mode = openshell` | Places the supervisor on the managed Docker bridge network. |
| `cap_add` | Grants supervisor-only capabilities required for namespace setup and process inspection. |
| `apparmor=unconfined` | Avoids Docker's default profile blocking required mount operations. |
| `restart_policy = unless-stopped` | Keeps managed sandboxes resumable across daemon or gateway restarts. |
| `PidsLimit` | Enforces the sandbox PID budget at the Docker cgroup layer. Set `[openshell.drivers.docker].sandbox_pids_limit = 0` to inherit the Docker/runtime default. |
| CDI GPU request | Uses opaque `driver_config.cdi_devices` values when set; otherwise selects the requested count of NVIDIA CDI GPUs in round-robin order when daemon CDI support is detected. Docker daemon `/info` can permit `nvidia.com/gpu=all` as a WSL2 all-only compatibility fallback, where it counts as one selectable device. Exact CDI device lists must not contain duplicates and must match the effective GPU count. |

The agent child process does not retain these supervisor privileges.

## Driver Config Mounts

The gateway forwards the `docker` block from `--driver-config-json` to this
driver. The driver accepts user-supplied `mounts` entries with these Docker
mount types:

- `bind`: mounts an absolute host path when `[openshell.drivers.docker]`
  has `enable_bind_mounts = true`.
- `volume`: mounts an existing Docker named volume. The driver validates that
  the volume exists before provisioning and never creates or removes it.
  Docker local-driver volumes created with bind options are treated as host
  bind mounts and require `enable_bind_mounts = true`.
- `tmpfs`: mounts an in-memory filesystem with optional `options`,
  `size_bytes`, and `mode`.

Host bind mounts are disabled by default because they expose gateway host
paths to sandbox requests. Image mounts are not part of the Docker
driver-config schema. The driver still uses internal bind mounts for
OpenShell-owned supervisor, token, and TLS material.

Docker `bind` mounts accept `source`, `target`, optional `read_only`, and an
optional `selinux_label` of `shared` (applies `:z`) or `private` (applies
`:Z`) for SELinux-enforcing hosts. Docker `volume` mounts may include
`subpath`. User-supplied bind and volume mounts are read-only by default; set
`read_only: false` to make them writable. Mount `source`, `target`, and
`subpath` values must not contain surrounding whitespace. Mount targets must be
absolute container paths and must not replace the workspace root (`/sandbox`)
or overlap OpenShell supervisor files, `/etc/openshell`, `/etc/openshell-tls`,
or `/run/netns`.

Example named-volume usage:

```shell
docker volume create openshell-work

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

## Supervisor Binary Resolution

The Docker driver bind-mounts a host-side Linux `openshell-sandbox` binary into
each sandbox container. Resolution order is:

1. `supervisor_bin` in `[openshell.drivers.docker]`.
2. `supervisor_image` in `[openshell.drivers.docker]`, extracting
   `/openshell-sandbox` from that image.
3. A sibling `openshell-sandbox` next to the running `openshell-gateway` binary.
4. A local Linux cargo target build for the Docker daemon architecture.
5. The release-matched default supervisor image, extracting `/openshell-sandbox`.

Release and Docker-image gateway builds bake the matching supervisor image tag
into the binary at compile time. The default Docker supervisor image is not
`:latest` unless a custom build explicitly sets that tag.

## Callback and TLS

`OPENSHELL_ENDPOINT` is injected from the gateway's configured gRPC endpoint.
When no endpoint is configured, the driver uses
`host.openshell.internal:<gateway-port>` with the appropriate HTTP or HTTPS
scheme. Set `host_gateway_ip` only when the host has an explicit, locally
assigned address that containers should use for callbacks; package-managed
macOS gateways should leave it unset.

For HTTPS endpoints, the server certificate must include the endpoint host as a
subject alternative name. Docker sandboxes also need the client TLS bundle
mounted into the container and exposed with:

- `OPENSHELL_TLS_CA`
- `OPENSHELL_TLS_CERT`
- `OPENSHELL_TLS_KEY`

HTTP endpoints reject TLS material because the supervisor would not use it.

## Environment Ownership

The driver merges template environment and sandbox spec environment first, then
overwrites security-critical keys:

- `OPENSHELL_ENDPOINT`
- `OPENSHELL_SANDBOX_ID`
- `OPENSHELL_SANDBOX`
- `OPENSHELL_SSH_SOCKET_PATH`
- `OPENSHELL_SANDBOX_COMMAND`
- TLS path variables when HTTPS is enabled

Do not allow sandbox images or templates to override these values.