External Standalone Subsystems

Overview: For modular enterprise platforms and plugin ecosystems, Foundry supports External Standalone Subsystems, allowing dynamic discovery and mounting of subsystem directories via subsystem.json manifests without recompiling the main Rust binary.

1. Directory Structure

my-app/
├── Cargo.toml
├── src/main.rs
└── external_systems/
    └── analytics/
        ├── subsystem.json              # Subsystem manifest specification
        └── custom_pages/               # Sandboxed admin views
            └── dashboard.html

2. Manifest Specification (`subsystem.json`)

{
  "slug": "analytics",
  "display_name": "Analytics Dashboard",
  "description": "Real-time traffic and conversion insights",
  "version": "1.0.0",
  "custom_pages": [
    {
      "key": "dashboard",
      "title": "Traffic Monitor",
      "icon": "BarChart3",
      "page_type": "iframe",
      "entry": "/api/v1/s/analytics/ext/custom-pages/dashboard.html",
      "required_role": null
    }
  ]
}

3. Dynamic Discovery in `main.rs`

use foundry::prelude::*;
use foundry_engine::external::load_external_subsystems;
use std::path::PathBuf;

#[foundry::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let config = FoundryConfig::from_env();
    let external_dirs = vec![PathBuf::from("./external_systems")];

    let modules = load_external_subsystems(&external_dirs);
    let mut builder = FoundryApp::builder().config(config);

    for m in modules {
        builder = builder.register_boxed_subsystem(m);
    }

    let app = builder.build().await?;
    app.run().await?;
    Ok(())
}