* `summary`: A short summary of the API.
* `description`: The description of your API, this can include markdown and will be shown in the docs.
* `routes`: A list of routes, these are each of the registered *path operations*. They are taken from `app.routes`.

/// info

The parameter `summary` is available in OpenAPI 3.1.0 and above, supported by FastAPI 0.99.0 and above.

///

[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]

{* ../../docs_src/openapi_callbacks/tutorial001.py hl[35] *}

/// tip

Notice that you are not passing the router itself (`invoices_callback_router`) to `callback=`, but the attribute `.routes`, as in `invoices_callback_router.routes`.

///

### Check the docs { #check-the-docs }

      contents: read  # for actions/checkout to fetch code
    name: "${{ matrix.root-pom }} on JDK ${{ matrix.java }} on ${{ matrix.os }}"
    strategy:
      matrix:
        os: [ ubuntu-latest ]
        java: [ 8, 11, 17, 21 ]
        root-pom: [ 'pom.xml', 'android/pom.xml' ]
        include:
          - os: windows-latest
            java: 21
            root-pom: pom.xml
    runs-on: ${{ matrix.os }}
    env:

		}
		pReader := NewPutObjReader(hashReader)
		_, err = er.PutObject(ctx, bucket, object, pReader, ropts)
		return setRestoreHeaderFn(oi, toObjectErr(err, bucket, object))
	}

	res, err := er.NewMultipartUpload(ctx, bucket, object, ropts)
	if err != nil {
		return setRestoreHeaderFn(oi, err)
	}

	var uploadedParts []CompletePart
	var rs *HTTPRangeSpec

And `items.router` contains the `APIRouter` inside of the file `app/routers/items.py`.

///

With `app.include_router()` we can add each `APIRouter` to the main `FastAPI` application.

It will include all the routes from that router as part of it.

/// note | Technical Details

It will actually internally create a *path operation* for each *path operation* that was declared in the `APIRouter`.

Do you want to just have a `str`? Or just a `dict`? Or a database class model instance directly? It all works the same way.

You actually don't have users that log in to your application but robots, bots, or other systems, that have just an access token? Again, it all works the same.

            method.setAccessible(true);
            method.invoke(multiChannelManager, null, null);
        });

        // Check that the root cause is CIFSException
        assertTrue(exception instanceof java.lang.reflect.InvocationTargetException);
        Throwable cause = ((java.lang.reflect.InvocationTargetException) exception).getCause();

If you try interacting with any of the two user interfaces, they will work correctly, because the browser will be able to talk to each specific app or sub-app.

### Technical Details: `root_path` { #technical-details-root-path }

When you mount a sub-application as described above, FastAPI will take care of communicating the mount path for the sub-application using a mechanism from the ASGI specification called a `root_path`.

* <a href="https://github.com/OAI/OpenAPI-Specification" class="external-link" target="_blank"><strong>OpenAPI</strong></a> for API creation, including declarations of <abbr title="also known as: endpoints, routes">path</abbr> <abbr title="also known as HTTP methods, as POST, GET, PUT, DELETE">operations</abbr>, parameters, request bodies, security, etc.