Persistent sandboxes

A persistent sandbox is one sandbox whose files outlive the container that runs it. It runs in sessions: each one up to an hour, paused after five idle minutes, and resumed with the files the last one left.

Sessions come and go, the files stay

Session 1 pauses after five idle minutes. The next call to session() starts session 2 from the files session 1 left.

Declare a box

src/DevBox.ts

import * as Modal from "@alchemy.run/modal";
import { Coder, Warm } from "./Coder.ts";

export const DevBox = Modal.PersistentSandbox("DevBox", { app: Coder, image: Warm, workdir: "/work" });

Resume it from a Worker

// construction phase
const box = yield* Modal.ConnectSandbox(DevBox);
// in fetch:
const session = yield* box.session();
const status = yield* session.exec("git status");

session() returns the running session, or resumes the box from its last session’s files.

Create one per user while your app runs

const box = yield* sandboxes.createPersistent({ image: "node:22-bookworm" });
// store box.persistentSandboxId with the user

Persistent sandboxes are experimental on Modal: no names, GPUs, env or tags yet.