@useatlas/railway-sandbox

Ephemeral Railway microVM isolation via the Railway Sandboxes SDK.

⚠ Security caveat — read before adopting. Railway Sandboxes offer only ISOLATED (outbound internet via NAT) and PRIVATE (private network + outbound internet) network modes — neither blocks outbound egress. A compromised or malicious explore command can phone home, which makes this a strictly weaker isolation posture than a deny-all backend (e.g. Vercel Sandbox with networkPolicy: "deny-all"). This plugin always creates sandboxes in ISOLATED mode (never PRIVATE), reports security.networkIsolation: false honestly, and is suitable for single-tenant / self-hosted deployments that accept the trade-off. It is not suitable for multi-tenant SaaS until Railway ships a no-egress mode (#3231).

Install

bun add @useatlas/railway-sandbox railway

Usage

import { defineConfig } from "@atlas/api/lib/config";
import { railwaySandboxPlugin } from "@useatlas/railway-sandbox";

// On Railway, RAILWAY_API_TOKEN / RAILWAY_ENVIRONMENT_ID are picked up
// automatically by the SDK:
export default defineConfig({
  plugins: [railwaySandboxPlugin({})],
});

// Or pass credentials explicitly:
export default defineConfig({
  plugins: [
    railwaySandboxPlugin({
      token: process.env.RAILWAY_API_TOKEN!,
      environmentId: process.env.RAILWAY_ENVIRONMENT_ID!,
    }),
  ],
});

Config

| Field | Type | Default | Description | |-------|------|---------|-------------| | token | string? | RAILWAY_API_TOKEN env | Railway API token | | environmentId | string? | RAILWAY_ENVIRONMENT_ID env | Environment to create sandboxes in | | idleTimeoutMinutes | number | 10 | Idle backstop (1–120). Railway destroys the sandbox after this much idle time even if close() never runs | | timeoutSec | number | 30 | Command timeout in seconds |

Behavior notes

• Lifecycle. The sandbox is destroyed eagerly when the cached backend is evicted (close() → destroy()); idleTimeoutMinutes is the billing backstop for leaked sandboxes. Health checks create + destroy a sandbox with a 1-minute backstop.
• File upload. The Railway SDK has no bulk file API ("use exec or SSH"), so the semantic tree is uploaded as base64 inside batched exec commands. Symlinks escaping the semantic root are skipped, matching the other sandbox backends.
• Per-environment sandbox cap. Railway caps sandboxes per environment — 10 (Trial/Free), 50 (Hobby), 100 (Pro/Enterprise); only CREATING/RUNNING count. Atlas caches one explore backend per semantic root (per org), so more concurrently-active orgs than the cap will fail create() — the error message surfaces the cap and the remedy (destroy idle sandboxes, wait for idle timeouts, or upgrade the plan).
• Beta SDK. Railway Sandboxes are in Priority Boarding; the SDK "may change in breaking ways between releases". Soak in staging before relying on it.

Reference

• Railway Sandboxes docs
• Plugin SDK docs
• Authoring guide