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Local development

To test your Dispatch Worker, user Worker and Outbound Worker before deploying to production, you can use Wrangler for development and testing.

1. Create a user worker

Terminal window
npm create cloudflare@latest -- customer-worker-1

For setup, select the following options:

  • For What would you like to start with?, choose Hello World Starter.
  • For Which template would you like to use?, choose Worker only.
  • For Which language do you want to use?, choose JavaScript.
  • For Do you want to use git for version control?, choose Yes.
  • For Do you want to deploy your application?, choose No (we will be making some changes before deploying).

Then, move into the newly created directory:

Terminal window
cd customer-worker-1

Update the src/index.js file for customer-worker-1:

export default {
  async fetch(request) {
    // make a subrequest to the internet
    const response = await fetch("https://example.com");
    return new Response(
      `user worker got "${await response.text()}" from fetch`,
    );
  },
};

Update the Wrangler file for customer-worker-1 and add the dispatch namespace:

{
  "dispatch_namespace": "my-namespace"
}

2. Create a dispatch worker

Terminal window
npm create cloudflare@latest -- dispatch-worker

For setup, select the following options:

  • For What would you like to start with?, choose Hello World Starter.
  • For Which template would you like to use?, choose Worker only.
  • For Which language do you want to use?, choose JavaScript.
  • For Do you want to use git for version control?, choose Yes.
  • For Do you want to deploy your application?, choose No (we will be making some changes before deploying).

Then, move into the newly created directory:

Terminal window
cd dispatch-worker

Update the src/index.js file for dispatch-worker:

export default {
  async fetch(request, env) {
    // get the user Worker, specifying parameters that the Outbound Worker will see when it intercepts a user worker's subrequest
    const customerScript = env.DISPATCH_NAMESPACE.get(
      "customer-worker-1",
      {},
      {
        outbound: {
          paramCustomerName: "customer-1",
        },
      },
    );
    // invoke user Worker
    return await customerScript.fetch(request);
  },
};

Update the Wrangler file for dispatch-worker and add the dispatch namespace binding:

{
  "dispatch_namespaces": [
    {
      "binding": "DISPATCH_NAMESPACE",
      "namespace": "my-namespace",
      "outbound": {
        "service": "outbound-worker",
        "parameters": [
          "paramCustomerName"
        ]
      }
    }
  ]
}

3. Create an Outbound Worker

Terminal window
npm create cloudflare@latest -- outbound-worker

For setup, select the following options:

  • For What would you like to start with?, choose Hello World Starter.
  • For Which template would you like to use?, choose Worker only.
  • For Which language do you want to use?, choose JavaScript.
  • For Do you want to use git for version control?, choose Yes.
  • For Do you want to deploy your application?, choose No (we will be making some changes before deploying).

Then, move into the newly created directory:

Terminal window
cd outbound-worker

Update the src/index.js file for outbound-worker:

export default {
  async fetch(request, env) {
    const { paramCustomerName } = env;
    // use the parameters passed by the dispatcher to know what this user this request is for
    // and return custom content back to the user worker
    return new Response(
      `intercepted a request for ${paramCustomerName} by the outbound`,
    );
  },
};

4. Start local dev session for your Workers

In separate terminals, start a local dev session for each of your Workers.

For your dispatcher Worker:

Terminal window
cd dispatch-worker
npx wrangler@dispatch-namespaces-dev dev --port 8600

For your outbound Worker:

Terminal window
cd outbound-worker
npx wrangler@dispatch-namespaces-dev dev --port 8601

And for your user Worker:

Terminal window
cd customer-worker-1
npx wrangler@dispatch-namespaces-dev dev --port 8602

5. Test your requests

Send a request to your dispatcher Worker:

Terminal window
curl http://localhost:8600
# -> user worker got "intercepted a request for customer-1 by the outbound" from fetch