This is different from using an `APIRouter` as a mounted application is completely independent. The OpenAPI and docs from your main application won't include anything from the mounted application, etc.

You can read more about this in the [Advanced User Guide](../advanced/index.md){.internal-link target=_blank}.

## Details

This sub-application is just another standard FastAPI application, but this is the one that will be "mounted":

```Python hl_lines="11  14-16"
{!../../../docs_src/sub_applications/tutorial001.py!}
```

### Mount the sub-application

In your top-level application, `app`, mount the sub-application, `subapi`.

In this case, it will be mounted at the path `/subapi`:

```Python hl_lines="11  19"

// under the procfs, /proc/<pid>/ns/net. In majority of cases, this is not used directly, but is rather bind mounted to
// /var/run/netns/<name>. However, this pattern is not ubiquitous. Some platforms bind mount to other places. As we run
// in a pod, we cannot just access any arbitrary file they happen to bind mount in, as we don't know ahead of time where
// it might be.
//
// Instead, we rely directly on the procfs.

// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package disk

import "runtime"

// IsRootDisk returns if diskPath belongs to root-disk, i.e the disk mounted at "/"
func IsRootDisk(diskPath string, rootDisk string) (bool, error) {
	if runtime.GOOS == "windows" {
		// On windows this function is not implemented.
		return false, nil
	}
	return SameDisk(diskPath, rootDisk)

	"ef53":     "EXT4",
	"f15f":     "ecryptfs",
	"794c7630": "overlayfs",
	"2fc12fc1": "zfs",
	"ff534d42": "cifs",
	"53464846": "wslfs",
}

// getFSType returns the filesystem type of the underlying mounted filesystem
func getFSType(ftype int64) string {
	fsTypeHex := strconv.FormatInt(ftype, 16)
	fsTypeString, ok := fsType2StringMap[fsTypeHex]
	if !ok {
		return "UNKNOWN"
	}
	return fsTypeString

// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package disk

// getFSType returns the filesystem type of the underlying mounted filesystem
func getFSType(fstype []int8) string {
	b := make([]byte, len(fstype))
	for i, v := range fstype {
		b[i] = byte(v)
	}
	return string(b)

  // being periodically called to reflect any possible change in the mounted
  // volume. This field defaults to false.
  //
  // Note: After a successful initial NodePublishVolume call, subsequent calls
  // to NodePublishVolume should only update the contents of the volume. New
  // mount points will not be seen by a running container.
  //
  // +optional
  optional bool requiresRepublish = 7;

  // being periodically called to reflect any possible change in the mounted
  // volume. This field defaults to false.
  //
  // Note: After a successful initial NodePublishVolume call, subsequent calls
  // to NodePublishVolume should only update the contents of the volume. New
  // mount points will not be seen by a running container.
  //
  // +optional
  optional bool requiresRepublish = 7;

    - mountPath: /etc/istio/proxy
      name: istio-envoy
    - mountPath: /var/run/secrets/tokens
      name: istio-token
    {{- if .Values.global.mountMtlsCerts }}
    # Use the key and cert mounted to /etc/certs/ for the in-cluster mTLS communications.
    - mountPath: /etc/certs/
      name: istio-certs
      readOnly: true
    {{- end }}
    - name: istio-podinfo
      mountPath: /etc/istio/pod

func mkdirAllIgnorePerm(path string) error {
	err := os.MkdirAll(path, 0o700)
	if err != nil {
		// It is possible in kubernetes like deployments this directory
		// is already mounted and is not writable, ignore any write errors.
		if osIsPermission(err) {
			err = nil
		}
	}
	return err
}

func getConfigFile() string {
	return filepath.Join(globalConfigDir.Get(), minioConfigFile)
}