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).

## Details { #details }

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

{* ../../docs_src/sub_applications/tutorial001_py310.py hl[11, 14:16] *}

### Mount the sub-application { #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`:

{* ../../docs_src/sub_applications/tutorial001_py310.py hl[11, 19] *}

import org.jspecify.annotations.NullUnmarked;
import org.jspecify.annotations.Nullable;

/**
 * An unbounded {@linkplain BlockingQueue blocking queue} that uses the same ordering rules as class
 * {@link PriorityQueue} and supplies blocking retrieval operations. While this queue is logically
 * unbounded, attempted additions may fail due to resource exhaustion (causing {@code

TFCI_WHL_IMPORT_TEST_ENABLE=1
TFCI_PYTHON_VERIFY_PIP_INSTALL_ARGS=""

# Used to simulate a T:\ drive within the container, to a limited extent,
# via a symlink.
# Helpful since the internal CI utilizes a T:\ drive, part of which is mounted
# to the container, and would result in C:\<path> != T:\<path> mismatches,
# when using variables like `TFCI_OUTPUT_DIR` in `docker exec commands,
# requiring conditional path adjustments throughout the CI scripts.

```html
<a href="/items/42">
```

## Templates and static files { #templates-and-static-files }

You can also use `url_for()` inside of the template, and use it, for example, with the `StaticFiles` you mounted with the `name="static"`.

```jinja hl_lines="4"
{!../../docs_src/templates/templates/item.html!}
```

In this example, it would link to a CSS file at `static/styles.css` with:

```CSS hl_lines="4"

* the lifespan event: das Lifespan-Event
* the lock: der Lock
* the locking: das Locking
* the mobile application: die Mobile-Anwendung
* the model object: das Modellobjekt
* the mounting: das Mounten
* mounted: gemountet
* the origin: das Origin
* the override: Die Überschreibung
* the parameter: der Parameter
* the parameters (plural): die Parameter
* the function parameter: der Funktionsparameter

        try {
            while ((len = reader.read(buf, size, bufferSize - size)) != -1) {
                size += len;
                if (size == bufferSize) {
                    // Enforce MAX_BUF_SIZE to prevent unbounded memory growth
                    final int newBufferSize = bufferSize + initialCapacity;
                    if (newBufferSize > MAX_BUF_SIZE) {

  // TODO(srbs): It seems like this is used only for performance optimization
  // and not for correctness. The only downside of keeping this 1 seems to be
  // that the gradient accumulation is unbounded and we will never
  // aggressively aggregate accumulated gradients to recover memory.
  // Revisit and fix.
  return 1;
}

// Consumes references to the tensors in the gradient_tensors list and returns

/// info | Very Technical Details

**Note**: this is a very technical detail that you probably can **just skip**.

---

The `APIRouter`s are not "mounted", they are not isolated from the rest of the application.

This is because we want to include their *path operations* in the OpenAPI schema and the user interfaces.

- Fixed a race condition that could result in erroneous volume unmounts for flex volume plugins during kubelet restart. ([#127669](https://github.com/kubernetes/kubernetes/pull/127669), [@olyazavr](https://github.com/olyazavr))