This is cool that we can create encapsulated instantiations of the software services we've created. But the promise was to use the Dockerized application for deployment on cloud services. In other words, we need to take all this learning and apply it to the task of deploying Notes on a public internet server with a fairly high degree of security.

We've demonstrated that, with Docker, Notes can be decomposed into four containers that have a high degree of isolation from each other, and from the outside world. 

There is another glaring problem: our process in the previous section was partly manual, partly automated. We created scripts to launch each portion of the system, which is a good practice according to the Twelve Factor Application model. But we did not automate the entire process to bring up Notes and the authentication services. Nor is this solution scalable beyond one machine.

Let's start with the last issue first—scalability. Within the Docker ecosystem, several Docker orchestrator services are available. An Orchestrator automatically deploys and manages Docker containers over a group of machines. Some examples of Docker Orchestrators are Docker Swarm (which is built into the Docker CLI), Kubernetes, CoreOS Fleet, and Apache Mesos. These are powerful systems able to automatically increase/decrease resources as needed, to move containers from one host to another, and more. We mention these systems for your further study as your needs grow.

Docker compose (https://docs.docker.com/compose/overview/) will solve the other problems we've identified. It lets us easily define and run several Docker containers together as a complete application. It uses a YAML file, docker-compose.yml, to describe the containers, their dependencies, the virtual networks, and the volumes. While we'll be using it to describe the deployment onto a single host machine, Docker compose can be used for multimachine deployments, especially when combined with Docker Swarm. Understanding Docker compose will provide a basis upon which to understand/use the other tools, such as Swarm or Kubernetes.

Docker machine (https://docs.docker.com/machine/overview/) is a tool for installing Docker Engine on virtual hosts, either local or remote, and for managing Docker containers on those hosts. We'll be using this to provision a server on a cloud hosting service, and push containers into that server. It can also be used to provision a virtual host on your laptop within a VirtualBox instance.

Before proceeding, ensure Docker compose and Docker machine are installed. If you've installed Docker for Windows or Docker for Mac, both are installed along with everything else. On Linux, you must install both separately by following the instructions at the links given earlier.