func registerAPIRouter(router *mux.Router) {
	// Initialize API.
	api := objectAPIHandlers{
		ObjectAPI: newObjectLayerFn,
	}

	// API Router
	apiRouter := router.PathPrefix(SlashSeparator).Subrouter()

	var routers []*mux.Router
	for _, domainName := range globalDomainNames {
		if IsKubernetes() {

* Es gibt ein Unterverzeichnis `app/routers/` mit einer weiteren Datei `__init__.py`, es handelt sich also um ein „Python-Subpackage“: `app.routers`.
* Die Datei `app/routers/items.py` befindet sich in einem Package, `app/routers/`, also ist sie ein Submodul: `app.routers.items`.
* Das Gleiche gilt für `app/routers/users.py`, es ist ein weiteres Submodul: `app.routers.users`.

* There's a subdirectory `app/routers/` with another file `__init__.py`, so it's a "Python subpackage": `app.routers`.
* The file `app/routers/items.py` is inside a package, `app/routers/`, so, it's a submodule: `app.routers.items`.
* The same with `app/routers/users.py`, it's another submodule: `app.routers.users`.

* Здесь также находится подкаталог `app/routers/`, содержащий `__init__.py`.  Он является суб-пакетом: `app.routers`.
* Файл `app/routers/items.py` находится внутри пакета `app/routers/`. Таким образом, он является суб-модулем: `app.routers.items`.
* Точно также `app/routers/users.py` является ещё одним суб-модулем: `app.routers.users`.

* 📤 `app/dependencies.py` 📁, 💖 `app/main.py`, ⚫️ "🕹": `app.dependencies`.
* 📤 📁 `app/routers/` ⏮️ ➕1️⃣ 📁 `__init__.py`, ⚫️ "🐍 📦": `app.routers`.
* 📁 `app/routers/items.py` 🔘 📦, `app/routers/`,, ⚫️ 🔁: `app.routers.items`.
* 🎏 ⏮️ `app/routers/users.py`, ⚫️ ➕1️⃣ 🔁: `app.routers.users`.
* 📤 📁 `app/internal/` ⏮️ ➕1️⃣ 📁 `__init__.py`, ⚫️ ➕1️⃣ "🐍 📦": `app.internal`.

* Hay un subdirectorio `app/routers/` con otro archivo `__init__.py`, por lo que es un "subpaquete de Python": `app.routers`.
* El archivo `app/routers/items.py` está dentro de un paquete, `app/routers/`, por lo que es un submódulo: `app.routers.items`.
* Lo mismo con `app/routers/users.py`, es otro submódulo: `app.routers.users`.

* Há um subdiretório `app/routers/` com outro arquivo `__init__.py`, então ele é um "subpacote Python": `app.routers`.
* O arquivo `app/routers/items.py` está dentro de um pacote, `app/routers/`, portanto, é um "submódulo": `app.routers.items`.
* O mesmo com `app/routers/users.py`,  ele é outro submódulo: `app.routers.users`.

///

### Add the callback router { #add-the-callback-router }

At this point you have the *callback path operation(s)* needed (the one(s) that the *external developer*  should implement in the *external API*) in the callback router you created above.

Now use the parameter `callbacks` in *your API's path operation decorator* to pass the attribute `.routes` (that's actually just a `list` of routes/*path operations*) from that callback router:

[providers]
  [providers.file]
    filename = "routes.toml"
```

This tells Traefik to listen on port 9999 and to use another file `routes.toml`.

/// tip

We are using port 9999 instead of the standard HTTP port 80 so that you don't have to run it with admin (`sudo`) privileges.

///

Now create that other file `routes.toml`:

```TOML hl_lines="5  12  20"
[http]
  [http.middlewares]

    queue.addListener(listener, directExecutor());

    Multiset<Object> counters = ConcurrentHashMultiset.create();
    queue.enqueue(incrementingEvent(counters, listener, 1));
    queue.enqueue(incrementingEvent(counters, listener, 2));
    queue.enqueue(incrementingEvent(counters, listener, 3));
    queue.enqueue(incrementingEvent(counters, listener, 4));
    assertEquals(0, counters.size());
    queue.dispatch();