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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.

Outbound Workers diagram information

​​ General Use Cases

Outbound Workers can be used to:

  • Log all subrequests to identify malicious domains 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’s wrangler.toml. Optionally, to pass data from your dynamic dispatch Worker to the Outbound Worker, the variable names can be specified under parameters.

Make sure that you have [email protected] or later installed.

binding = "dispatcher"
namespace = "<NAMESPACE_NAME>"
outbound = {service = "<SERVICE_NAME>", parameters = ["params_object"]}
  1. Edit your dynamic dispatch Worker to call the Outbound Worker and declare variables to pass on dispatcher.get().
export default {
async fetch(request, env) {
try {
// parse the URL, read the subdomain
let workerName = new URL(request.url).host.split('.')[0];
let context_from_dispatcher = {
'customer_name': workerName,
'url': request.url,
let userWorker = env.dispatcher.get(
{// outbound arguments. object name must match parameters in the binding
outbound: {
params_object: context_from_dispatcher,
return await userWorker.fetch(request);
} catch (e) {
if (e.message.startsWith('Worker not found')) {
// we tried to get a worker that doesn't exist in our dispatch namespace
return new Response('', { status: 404 });
return new Response(e.message, { status: 500 });
  1. 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>.

The following is an example of an Outbound Worker that logs the fetch request from user Worker and creates a JWT if the fetch request matches

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
method: 'POST',
body: JSON.stringify({
const url = new URL(original_url);
if ( === '') {
// 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)