* Memory
* Previous steps before starting

We'll see how they would affect **deployments**.

In the end, the ultimate objective is to be able to **serve your API clients** in a way that is **secure**, to **avoid disruptions**, and to use the **compute resources** (for example remote servers/virtual machines) as efficiently as possible. 🚀

## Setting up your development environment

In order to make changes to Gradle, you'll need:

* A [Java Development Kit](http://jdk.java.net/) (JDK) **version 11**. Fixed version is required to use [remote cache](#remote-build-cache). 
* A text editor or IDE. We use and recommend [IntelliJ IDEA CE](http://www.jetbrains.com/idea/).  IntelliJ Ultimate will also work. You'll need IntelliJ 2021.2.2 or newer.

              SynchronousQueue(),
              threadFactory("$okHttpName Dispatcher", false),
            )
        }
        return executorServiceOrNull!!
      }

  /** Ready async calls in the order they'll be run. */
  private val readyAsyncCalls = ArrayDeque<AsyncCall>()

  /** Running asynchronous calls. Includes canceled calls that haven't finished yet. */
  private val runningAsyncCalls = ArrayDeque<AsyncCall>()

But it's not possible to have a running container without **at least one running process**. If the main process stops, the container stops.

## Build a Docker Image for FastAPI

Okay, let's build something now! 🚀

I'll show you how to build a **Docker image** for FastAPI **from scratch**, based on the **official Python** image.

This is what you would want to do in **most cases**, for example:

* Using **Kubernetes** or similar tools

* Security - HTTPS
* Running on startup
* Restarts
* Replication (the number of processes running)
* Memory
* Previous steps before starting

        return true
      }
    }

    // If we have a routes left, use 'em.
    if (routeSelection?.hasNext() == true) return true

    // If we haven't initialized the route selector yet, assume it'll have at least one route.
    val localRouteSelector = routeSelector ?: return true

    // If we do have a route selector, use its routes.
    return localRouteSelector.hasNext()
  }

  /**

Or you might have a native mobile application that communicates with your WebSocket backend directly, in native code.

Or you might have any other way to communicate with the WebSocket endpoint.

---

But for this example, we'll use a very simple HTML document with some JavaScript, all inside a long string.

This, of course, is not optimal and you wouldn't use it for production.

In production you would have one of the options above.

The only new thing is the `callbacks=invoices_callback_router.routes` as an argument to the *path operation decorator*. We'll see what that is next.

## Documenting the callback

The actual callback code will depend heavily on your own API app.

And it will probably vary a lot from one app to the next.

        // A connection will be ready to evict soon.
        return earliestEvictableIdleAtNs + keepAliveDurationNs - now
      }

      inUseConnectionCount > 0 -> {
        // All connections are in use. It'll be at least the keep alive duration 'til we run again.
        return keepAliveDurationNs
      }

      else -> {
        // No connections, idle or in use.
        return -1
      }
    }
  }

      }
      if (obj instanceof Wrapper) {
        Wrapper<?> that = (Wrapper<?>) obj; // note: not necessarily a Wrapper<T>

        if (this.equivalence.equals(that.equivalence)) {
          /*
           * We'll accept that as sufficient "proof" that either equivalence should be able to
           * handle either reference, so it's safe to circumvent compile-time type checking.
           */
          @SuppressWarnings("unchecked")