# Container Runtime — Node.js Service Manager

Node.js runtime that manages service containers via JSON-RPC. See `RPCSpec.md` in this directory for the full RPC protocol.

## Architecture

```
LXC Container (uniform base for all services)
└── systemd
    └── container-runtime.service
        └── Loads /usr/lib/startos/package/index.js (from s9pk javascript.squashfs)
            └── Package JS launches subcontainers (from images in s9pk)
```

The container runtime communicates with the host via JSON-RPC over Unix socket. Package JavaScript must export functions conforming to the `ABI` type defined in `sdk/base/lib/types.ts`.

## `/media/startos/` Directory (mounted by host into container)

| Path                 | Description                                           |
| -------------------- | ----------------------------------------------------- |
| `volumes/<name>/`    | Package data volumes (id-mapped, persistent)          |
| `assets/`            | Read-only assets from s9pk `assets.squashfs`          |
| `images/<name>/`     | Container images (squashfs, used for subcontainers)   |
| `images/<name>.env`  | Environment variables for image                       |
| `images/<name>.json` | Image metadata                                        |
| `backup/`            | Backup mount point (mounted during backup operations) |
| `rpc/service.sock`   | RPC socket (container runtime listens here)           |
| `rpc/host.sock`      | Host RPC socket (for effects callbacks to host)       |

## S9PK Structure

See `../core/s9pk-structure.md` for the S9PK package format.