<!--
SPDX-License-Identifier: CC-BY-SA-4.0
See LICENSE file for licensing information.
-->

> This documentation is organized by AI with reference to actual code. AI can make mistakes — please verify against the source code when in doubt.


# IOL Images with iol-runner (Cisco CML containerized IOL) as Docker Nodes

## Overview

IOL images packaged with Cisco CML's container runner — for example
`iol-xe/iol-xe:17-18-02` (IOS-XE 17.18.02 IOL in a scratch image driven by
`iol-runner`, module `virl.lab/cmd/iol-runner`) — run as first-class GNS3
Docker router nodes with **zero changes to the image**. The integration adds
two generic server mechanisms:

1. **Unix-socket NIO** (`GNS3_UNIX_SOCKET_NIO=1`, on `VendorDockerVM`): link
   adapters through per-interface AF_UNIX datagram sockets instead of a TAP
   interface moved into the container's network namespace.
2. **`IOLDockerVM`** (marker `GNS3_IOL_RUNNER=1`): generates the runner's
   config file per start, prepares its runtime directory and cleans up stale
   sockets — the iol-runner-specific glue on top of the vendor path.

## How the image works

```mermaid
graph LR
    subgraph Container["scratch container (PID 1)"]
        RUNNER["/iol-runner -config /config/iol-config.json -stdio"]
        IOL["IOL process<br/>(IOS-XE 17.18.02)"]
        NETIOMUX["netiomux"]
        SOCKETS["/tmp/s00.sock (recv)<br/>/tmp/c00.sock (send-to path)<br/>… one pair per interface"]
        RUNNER -->|"spawn -e/-s/-m + app id"| IOL
        IOL -->|"netio bus /tmp/netio&lt;uid&gt;/"| NETIOMUX --> SOCKETS
    end
    subgraph Host
        UBRIDGE["uBridge bridgeN<br/>add_nio_unix /proc/PID/root/tmp/cNN.sock …<br/>+ add_nio_udp (topology)"]
        VOL["project-files/docker/&lt;node&gt;/config<br/>(+ tmp/run nested bind)"]
    end
    SOCKETS <-->|"raw Ethernet frames via<br/>the container root in /proc"| UBRIDGE
    UBRIDGE -.->|"iol-config.json +<br/>persistent /tmp/run"| VOL
```

* **Console**: the runner muxes the IOS console onto PID 1 stdio (`-stdio`
  entrypoint flag). The plain `console_type: "telnet"` attaches to it — no
  `docker_exec` needed. The runner requires a TTY, which GNS3 always
  allocates; without one the runner exits (`inappropriate ioctl for device`).
* **Networking**: the runner does not touch the container's network
  namespace. Per interface N it creates, inside the container's `/tmp`: a
  receive socket `s%02d.sock` (frames sent there are injected into guest
  interface N) and a send-to path `c%02d.sock` (whoever binds it receives
  the guest's frames). Frames are **raw Ethernet**, one datagram per frame.
  uBridge reaches both through the container's root in `/proc`
  (`/proc/<container-pid>/root/tmp/…`) — a short path (AF_UNIX names are
  capped at 107 bytes, which a project directory path alone would exceed)
  that requires no volume mount and leaves the sockets ephemeral in the
  container, fresh in every container GNS3 creates.
* **Licensing**: the image ships a self-consistent `/etc/hostid` + `.iourc`
  pair, and the runner regenerates the license from the host ID at boot —
  nothing to configure.
* **Persistence**: `/tmp/run` (the IOL working directory) holds the NETMAP,
  the startup-config (`config`, plain IOS format) and NVRAM (`nvram_00001`).
  It is the only `/tmp` path that needs to survive: GNS3 bind-mounts the
  node directory's `tmp/run/` at `/tmp/run`, so the router's configuration
  survives stop/start and container recreation while everything else in
  `/tmp` stays ephemeral. The generated config maps the runner to the
  server's uid/gid (`user-id`/`group-id`), so all files it creates are owned
  by the server user — which is also what lets an unprivileged uBridge
  traverse `/proc/<pid>/root` to reach the container's sockets (no
  permission-fix pass needed).

## Template

```json
{
    "name": "IOS-XE 17.18.02 IOL",
    "template_type": "docker",
    "image": "iol-xe/iol-xe:17-18-02",
    "category": "router",
    "symbol": ":/symbols/router.svg",
    "adapters": 4,
    "console_type": "telnet",
    "environment": "GNS3_IOL_RUNNER=1",
    "extra_volumes": ["/config"],
    "memory": 2560
}
```

`/config` and `/tmp/run` are auto-added even if omitted; listing `/config`
keeps the template self-documenting.

## Server mechanisms

| Mechanism | Where | What it does |
|---|---|---|
| `GNS3_UNIX_SOCKET_NIO=1` | `VendorDockerVM` | `_add_ubridge_connection` override: `bridge create` + `bridge add_nio_unix /proc/<pid>/root<dir>/c{N:02d}.sock /proc/<pid>/root<dir>/s{N:02d}.sock` instead of TAP + `docker move_to_ns`. No TAP allocation, no `set_mac_addr`, namespace untouched, no volume required. |
| `GNS3_UNIX_SOCKET_DIR=<dir>` | `VendorDockerVM` | In-container socket directory (default `/tmp`). Any image whose agent exposes the `s%02d`/`c%02d` datagram pairs can use this without the IOL specifics. |
| `GNS3_IOL_RUNNER=1` | `IOLDockerVM` (selected in the manager) | Forces skip-init + unix-socket NIO + the `/config` and `/tmp/run` volumes; on every start writes `<node>/config/iol-config.json` (`num-eth` = adapter count, `num-serial` = 0, memory from `GNS3_IOL_MEMORY`, default 2048) and creates `<node>/tmp/run/` (the IOL process dies without it). |
| `restart()` hardening | `IOLDockerVM` | The base `docker restart` would boot the runner on a stale config and leave uBridge wired to the previous run's sockets; reload becomes graceful stop (SIGTERM → NVRAM flush) + full start. |

`GNS3_STOP_TIMEOUT` (default 60) controls the SIGTERM grace period on stop.
Extra iol-runner flags can be passed via `start_command`, e.g. `-keep`
(L1 keepalives) or `-debug 9` (verbose `process.log` — very useful when
diagnosing wiring issues).

## Notes and caveats

* **Memory sizing**: `memory` caps the whole container; the IOL process gets
  `GNS3_IOL_MEMORY` (default 2048 MB). Keep container memory at IOL memory
  + ~512 MB headroom or the OOM-killer will shoot the router.
* **MAC addresses**: the `mac_address` template field and per-adapter custom
  MACs are ignored — IOL derives its own scheme (`aabb.cc00.0XY0`).
* **Adapters**: change the adapter count while the node is stopped; the
  config is regenerated on the next start and the runner creates the
  matching socket set (IOL granularity is 4 ports per unit).
* **Stop before editing**: NVRAM is only flushed on a graceful stop (SIGTERM,
  "cleanup done" in `process.log`); a kill loses the running-config changes
  since the last `write memory`.
* **Class selection is create-time**: toggling `GNS3_IOL_RUNNER` via PUT
  takes effect after a project reload (same as `docker_exec`).
* The startup-config lives at `project-files/docker/<node>/tmp/run/config`;
  `extra_configs` targets under persisted volumes are warned against by the
  generic create path — edit the file directly or paste via the console.