Worker

Learn how to deploy, configure, and manage Cloudflare Workers using Alchemy for serverless functions at the edge.

This guide walks you through creating, testing, and deploying a Cloudflare Worker, then evolving it to use Durable Objects for session storage.

Create a Worker

Start by defining a Worker in your alchemy.run.ts file.

import alchemy from "alchemy";
import { Worker } from "alchemy/cloudflare";

const app = await alchemy("my-app");

export const worker = await Worker("api", {
  entrypoint: "./src/worker.ts",
  url: true, // Get a public URL
});

console.log({ url: worker.url });
await app.finalize();

Implement the Worker

Create your Worker script with a basic fetch handler.

import type { worker } from "../alchemy.run";

export default {
  async fetch(request: Request, env: typeof worker.Env): Promise<Response> {
    const url = new URL(request.url);

    return Response.json({
      message: "Hello from Alchemy!",
      path: url.pathname,
    });
  },
};

Test Locally

Run the Worker in development mode.
Terminal window
```
bun alchemy dev
```
Your Worker is now running locally and will auto-reload on code changes.
Deploy to Production

Deploy your Worker to Cloudflare’s edge network.
Terminal window
```
bun alchemy deploy
```
Your Worker is now live at the URL shown in the console.

Add Session Storage

Create a Durable Object namespace to store session data.

import alchemy from "alchemy";
import { Worker } from "alchemy/cloudflare";
import { Worker, DurableObjectNamespace } from "alchemy/cloudflare";

const app = await alchemy("my-app");

const sessions = DurableObjectNamespace("sessions", {
  className: "Session",
  sqlite: true,
});

export const worker = await Worker("api", {
  entrypoint: "./src/worker.ts",
  url: true,
  bindings: {
    SESSIONS: sessions,
  },
});

console.log({ url: worker.url });
await app.finalize();

Implement the Session Class

Create a Durable Object to handle session state.

import { DurableObject } from "cloudflare:workers";
import type { worker } from "../alchemy.run";

export class Session extends DurableObject {
  async fetch(request: Request) {
    const url = new URL(request.url);

    if (url.pathname === "/set") {
      const data = await request.json();
      await this.ctx.storage.put("data", data);
      return Response.json({ success: true });
    }

    const data = await this.ctx.storage.get("data");
    return Response.json({ data });
  }
}

Use Session from Worker

Update your Worker to use sessions based on a request header.

import { env } from "cloudflare:workers";
import type { worker } from "../alchemy.run";

export default {
  async fetch(request: Request, env: typeof worker.Env): Promise<Response> {
    const url = new URL(request.url);

    return Response.json({
      message: "Hello from Alchemy!",
      path: url.pathname,
    });
    const sessionId = request.headers.get("x-session-id") || "default";

    // Get the session Durable Object
    const id = env.SESSIONS.idFromName(sessionId);
    const session = env.SESSIONS.get(id);

    // Forward request to session
    return session.fetch(request);
  },
};

Test the Session

Test your session-enabled Worker locally.

# Set session data
curl -X POST http://localhost:8787/set \
  -H "x-session-id: user-123" \
  -H "Content-Type: application/json" \
  -d '{"name": "Alice", "theme": "dark"}'

# Get session data
curl http://localhost:8787 \
  -H "x-session-id: user-123"

Deploy Updated Worker

Deploy your session-enabled Worker to production.
Terminal window
```
bun alchemy deploy
```
Your Worker now persists session data across requests using Durable Objects.