Outbound Workers

Outbound Workers sit between your customer’s Workers and the public Internet. They give you visibility into all outgoing fetch() requests from user Workers.

​​ General Use Cases

Outbound Workers can be used to:

• Log all subrequests to identify malicious hosts or usage patterns.
• Create, allow, or block lists for hostnames requested by user Workers.
• Configure authentication to your APIs behind the scenes (without end developers needing to set credentials).

​​ Use Outbound Workers

To use Outbound Workers:

1. Create a Worker intended to serve as your Outbound Worker.
2. Outbound Worker can be specified as an optional parameter in the dispatch namespaces binding in a project wrangler.toml. Optionally, to pass data from your dynamic dispatch Worker to the Outbound Worker, the variable names must be specified under parameters.

Make sure that you have wrangler@3.3.0 or later installed.

wrangler.toml
[[dispatch_namespaces]]
binding = "dispatcher"
namespace = "<NAMESPACE_NAME>"
outbound = {service = "<SERVICE_NAME>", parameters = ["customer_name","url"]}

3. Edit your dynamic dispatch Worker to call the Outbound Worker and declare variables to pass on dispatcher.get().

index.js
export default {
  // this event is fired when the dispatched Workers make a subrequest
  async fetch(request, env, ctx) {
    // env contains the values we set in `dispatcher.get()`
    const customer_name = env.customer_name;
    const original_url = env.url;

    // log the request
    ctx.waitUntil(fetch(
      'https://logs.example.com',
      {
        method: 'POST',
        body: JSON.stringify({
          customer_name,
          original_url,
        }),
      },
    ));

    const url = new URL(original_url);
    if (url.host === 'api.example.com') {
      // pre-auth requests to our API
      const jwt = make_jwt_for_customer(customer_name);

      let headers = new Headers(request.headers);
      headers.set('Authorization', `Bearer ${jwt}`);

      // clone the request to set new headers using existing body
      let new_request = new Request(request, {headers});

      return fetch(new_request)
    }

    return fetch(request)
  }
};

4. The Outbound Worker will now be invoked on any fetch() requests from a user Worker. The user Worker will trigger a FetchEvent on the Outbound Worker. The variables declared in the binding can be accessed in the Outbound Worker through env.<VAR_NAME>.