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docs: document MCP server URL host resolution behavior

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Add documentation explaining how _server_url() resolves the host
when Server.host is 0.0.0.0 or :: — using the default route
interface IP instead of hardcoding 127.0.0.1.
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YueGuobin 2026-06-06 00:52:21 +08:00
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docs/features/mcp-service.md
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@ -231,10 +231,24 @@ sequenceDiagram
The `get_node_console_info` tool returns a WebSocket URL for connecting to a node's console. This endpoint is protocol-agnostic — it works for **telnet**, **ssh**, and **vnc** console types alike. The WebSocket simply proxies raw byte streams between the client and the compute node; protocol negotiation (e.g. SSH key exchange) happens on the compute side.
The WebSocket URL is constructed using the server's `_server_url()`, which resolves the host as follows:
| `Server.host` value | Resolved host in URL |
|:---|:---|
| Specific IP or hostname (e.g. `192.168.1.3`) | Used as-is |
| `0.0.0.0` (IPv4 any, default) | Detected via **default route interface IP** |
| `::` (IPv6 any) | Detected via default route interface IP |
| Detection failure | Fallback to `127.0.0.1` |
When `Server.host` is `0.0.0.0` (listen on all interfaces), the MCP server discovers the default route interface IP using a UDP socket connect to `8.8.8.8:80` — no network data is sent, the operating system simply selects the interface that would be used for the default route. This ensures the returned WebSocket URL uses a reachable address (e.g. `192.168.1.3` instead of `127.0.0.1`).
If the configured host is already a specific IP or hostname (not `0.0.0.0`), it is used directly in the URL without modification.
Use `websocat` to connect from the command line:
```bash
websocat wss://host:3080/v3/projects/{project_id}/nodes/{node_id}/console/ws?token=<jwt>
# The host in the URL is automatically resolved to a reachable address
websocat ws://192.168.1.3:3080/v3/projects/{project_id}/nodes/{node_id}/console/ws?token=<jwt>
```
### Source Files