## Mounting a **FastAPI** application

"Mounting" means adding a completely "independent" application in a specific path, that then takes care of handling everything under that path, with the _path operations_ declared in that sub-application.

### Top-level application

First, create the main, top-level, **FastAPI** application, and its *path operations*:

 * [IOException] if the call was canceled.
 */
class RetryAndFollowUpInterceptor(private val client: OkHttpClient) : Interceptor {
  @Throws(IOException::class)
  override fun intercept(chain: Interceptor.Chain): Response {
    val realChain = chain as RealInterceptorChain
    var request = chain.request
    val call = realChain.call
    var followUpCount = 0
    var priorResponse: Response? = null

  }

  public void testCheckElementIndex_badSize() {
    try {
      Preconditions.checkElementIndex(1, -1);
      fail();
    } catch (IllegalArgumentException expected) {
      // don't care what the message text is, as this is an invalid usage of
      // the Preconditions class, unlike all the other exceptions it throws
    }
  }

  public void testCheckElementIndex_negative() {
    try {

  }

  public void testCheckElementIndex_badSize() {
    try {
      Preconditions.checkElementIndex(1, -1);
      fail();
    } catch (IllegalArgumentException expected) {
      // don't care what the message text is, as this is an invalid usage of
      // the Preconditions class, unlike all the other exceptions it throws
    }
  }

  public void testCheckElementIndex_negative() {
    try {

If you look at it, *path operation functions* are declared to be used whenever a *path* and *operation* matches, and then **FastAPI** takes care of calling the function with the correct parameters, extracting the data from the request.

Actually, all (or most) of the web frameworks work in this same way.

You never call those functions directly. They are called by your framework (in this case, **FastAPI**).

## A "callable" instance

In Python there's a way to make an instance of a class a "callable".

Not the class itself (which is already a callable), but an instance of that class.

To do that, we declare a method `__call__`:

=== "Python 3.9+"

    ```Python hl_lines="12"
    {!> ../../../docs_src/dependencies/tutorial011_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="11"

   *
   * <p>Cancellation does not propagate from the output future to a callable that has begun to
   * execute, but if the output future is cancelled before {@link Callable#call()} is invoked,
   * {@link Callable#call()} will not be invoked.
   */
  public <T extends @Nullable Object> ListenableFuture<T> submit(
      Callable<T> callable, Executor executor) {
    checkNotNull(callable);

# Allow the root user to perform any action.
allow {
 input.owner == true
}

# All other users may do anything other than call PutObject
allow {
 input.action != "s3:PutObject"
 input.owner == false
}
EOF
```

Then load the policy via OPA's REST API.

```
curl -X PUT --data-binary @example.rego \
  localhost:8181/v1/policies/putobject
```

### 4. Setup MinIO with OPA

* Then it detects that it has to use the worker class at `uvicorn.workers.UvicornWorker`.
* And then it starts **4 workers**, each with its own PID: `19511`, `19513`, `19514`, and `19515`.

Gunicorn would also take care of managing **dead processes** and **restarting** new ones if needed to keep the number of workers. So that helps in part with the **restart** concept from the list above.

	ctx := newContext(r, w, "AssumeRole")

	claims := make(map[string]interface{})
	defer logger.AuditLog(ctx, w, r, claims)

	// Check auth here (otherwise r.Form will have unexpected values from
	// the call to `parseForm` below), but return failure only after we are
	// able to validate that it is a valid STS request, so that we are able
	// to send an appropriate audit log.
	user, apiErrCode := checkAssumeRoleAuth(ctx, r)