Staging machine setup

To start, you need to install and run Docker services on a staging machine running Ubuntu 18.04 LTS.

Update software repositories:
```
sudo apt-get update
```
Update your list of packages:
```
sudo apt update
```

Install the packages that allow the apt packaging tool to use packages over HTTPS:

sudo apt install apt-transport-https ca-certificates curl software-properties-common

Add the GPG (GNU Privacy Guard) key for the official Docker repository to your system:
```
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
```

Add the Docker repository to APT sources:

sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu bionic stable"

Update the package database with the Docker packages from the newly added repository:
```
sudo apt update
```
Make sure that you are about to install Docker from the Docker repository instead of from the default Ubuntu repository:
```
apt-cache policy docker-ce
```
You should see output like this, although the version number for Docker may differ:
```
docker-ce:
  Installed: (none)
  Candidate: 18.03.1~ce~3-0~ubuntu
  Version table:
     18.03.1~ce~3-0~ubuntu 500
        500 https://download.docker.com/linux/ubuntu bionic/stable amd64 Packages
```
Notice that docker-ce (Docker Community Edition) isn't installed, but that the Docker version candidate for installation is from the Docker repository for Ubuntu 18.04 (bionic).
Install Docker:
```
sudo apt install docker-ce
```

Docker should now be installed, the Docker service started, and the process enabled to start on boot. To confirm that the service is running, enter this command:

sudo systemctl status docker

You should see output like this, showing that the service is active and running:

docker.service - Docker Application Container Engine
  Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
  Active: active (running) since Thu 2018-07-05 15:08:39 UTC; 2min 55s ago
    Docs: https://docs.docker.com
Main PID: 10096 (dockerd)
   Tasks: 16
  CGroup: /system.slice/docker.service
          ├─10096 /usr/bin/dockerd -H fd://
          └─10113 docker-containerd --config /var/run/docker/containerd/containerd.toml

Installing Docker will now give you not only the Docker daemon (docker.service) but also the docker command-line utility, or the Docker client.

Install Docker:
```
sudo apt install docker.io
```