In this section, we will find out how to install Docker on Windows, macOS, and Linux operating systems. Next, we will run a sample hello-world image to verify the setup and check if everything works fine after the installation process.

Docker installation is quite straightforward, but there are some things you will need to focus on to make it run smoothly. We will point them out to make the installation process painless. You should know that Linux is the natural environment for Docker. If you run the container, it will run on a Linux kernel. If you run your container on Docker running on Linux, it will use the kernel of your own machine. This is not the case in macOS and Windows; that's the reason why the Linux kernel needs to be virtualized if you want to run a Docker container on these operating systems. The Docker engine, when running on macOS or MS Windows, will use the lightweight Linux distribution, made specifically to run Docker containers. It runs completely from RAM, using only several megabytes, and boots in a couple of seconds. After the installation of the main Docker package on macOS and Windows, the OS built-in virtualization engine will be used by default. Therefore, there are some special requirements for your machine. For the newest, native Docker setup, which is deeply integrated into native virtualization engines present in your operating system, you will need to have 64-bit Windows 10 professional or enterprise. For macOS, the newest Docker for Mac is a native Mac application developed from scratch, with a native user interface, integrated with OS X native virtualization, hypervisor framework, networking, and filesystem. The mandatory requirement will be Yosemite 10.10.3 or newer. Let's begin with installing on macOS.

To get the native Docker version for your Mac, head to the http://www.docker.com and then the Get Docker macOS section. Docker for Mac is a standard, native dmg package you can mount. You will find just a single application inside the package:

Now just move the Docker.app into your Applications folder, and you are all set. Couldn't be easier. If you run Docker, it will sit as a small whale icon in your macOS menu. The icon will animate during the Docker startup process and stabilize after it finishes:

• If you now click the icon, it will give you a handy menu with the Docker status and some additional options:

• Docker for Mac has an auto-update capability, which is great for keeping your installation up to date. The first Preferences... pane gives you the possibility to automatically check for updates; it's marked by default:

• If you are a brave soul, you can also switch to the beta channel for getting updates. This way you can always have the latest and greatest Docker features, with the risk of decreased stability, as is always the case with beta software. Also take note that switching to the beta channel will uninstall your current stable version of Docker and destroy all of your settings and containers. Docker will warn you about this, to make sure you really want to do it:

• The File Sharing pane of the Preferences... will give you an option to mark macOS directories on your machine to be bind mounted into Docker containers you are going to run later. We will explain mounting directories in detail later on in the book. For the time being, let's just have the default set of selected directories:

• The Advanced pane has some options to adjust the resources of your computer that will be available for Docker, it will be the number of processors and memory amount. The default settings are usually a good start if you begin with Docker on macOS:

• The Proxies pane gives you the possibility to setup a proxy, if you need it on your machine. You can opt for using system or manual settings, as you can see in the following screenshot:

• On the next page, you can edit some Docker daemon settings. This will include adding registries and registry mirrors. Docker will use them when pulling the image. The Advanced tab contains a text field, in which you can enter the JSON text containing the daemon config:

• In the Daemon pane, you can also turn off Docker Experimental features. For some time now, Experimental features have been enabled by default. From time to time, a new version of Docker comes with new Experimental features. At the time of writing this book, they will include, for example, Checkpoint & Restore (a feature that allows you to freeze a running container by checkpointing it), Docker graph driver plugins (to use an external/out-of-process graph driver for use with the Docker engine as an alternative to using the built-in storage drivers), and some others. It's always interesting to see what new features are included in the new version of Docker. Clicking the link in the Daemon page will take you to the GitHub page which lists and explains all the new experimental features.
• The last Preferences... pane is the Reset. If you find that your Docker won't start or behaves badly, you can try to reset the Docker installation to the factory defaults:

You should be warned though, that resetting Docker to the factory state will also remove all downloaded images and containers you may have on your machine. If you have images that have not been pushed anywhere yet, having a backup first is always a good idea.

The Open Kitematic in the Docker menu is a handy shortcut to open the Kitematic application we have mentioned earlier. It's a desktop utility for using Docker on Windows and Mac OS X. If you do not have Kitematic installed already, Docker will give you a link with the installation package:

• If you run Kitematic, it will present you the Docker Hub login screen first. You can now Sign up to the Docker Hub and then log in providing your username and password:

Clicking on Skip For Now will take you to the images list without logging into the Docker Hub. Let's test our installation by pulling and running an image. Let's search for hello-java-world, as seen on the following screenshot:

After pulling the image from the registry, start it. Kitematic will present the running Container logs, which will be the famous hello world message, coming from a containerized Java application:

That's it for running the container in Kitematic. Let's try to do the same from the shell. Execute the following in the terminal:

$ docker run milkyway/java-hello-world 

As a result, you will see the same greeting, coming from a containerized Java application, this time in the macOS terminal:

That's it, we have a native Docker up and running on our macOS. Let's install it on Linux, as well.

There are a lot of various Linux distributions out there and the installation process can be a little bit different for each Linux distribution. I'm going to install Docker on the latest, 16.04 Ubuntu desktop:

1. First, we need to allow the apt package manager to use a repository over the HTTPS protocol. Execute from the shell:

$ sudo apt-get install -y --no-install-recommends apt-transport-https ca-certificates curl software-properties-common

2. The next thing we are going to do is add Docker's apt repository gpg key to our apt sources list:

$ curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add –

3. A simple OK will be the response if succeeded. Use the following command to set up the stable repository:

$ sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"

4. Next, we need to update the apt packages index:

$ sudo apt-get update  

5. Now we need to make sure the apt installer will use the official Docker repository instead of the default Ubuntu repository (which may contain the older version of Docker):

$ apt-cache policy docker-ce  

6. Use this command to install the latest version of Docker:

$ sudo apt-get install -y docker-ce

7. The apt package manager will download a lot of packages; those will be the needed dependencies and the docker-engine itself:

8. That's it, you should be all set. Let's verify if Docker works on our Linux box:

$sudo docker run milkyway/java-hello-world  

9. As you can see, the Docker engine will pull the milkyway/java-hello-world image with all its layers from the Docker Hub and respond with a greeting:

But do we need to run Docker commands with sudo? The reason for that is the Docker daemon always runs as the root user, and since Docker version 0.5.2, the Docker daemon binds to a Unix socket instead of a TCP port. By default, that Unix socket is owned by the user root, and so, by default, you can access it with sudo. Let's fix it to be able to run the Docker command as a normal user:

1. First, add the Docker group if it doesn't already exist:

$ sudo groupadd docker

2. Then, add your own user to the Docker group. Change the username to match your preferred user:

$ sudo gpasswd -a jarek docker  

3. Restart the Docker daemon:

$ sudo service docker restart  

4. Now let's log out and log in again, and execute the docker run command one more time, without sudo this time. As you can see, you are now able to work with Docker as a normal, non-root user:

5. That's it. Our Linux Docker installation is ready to play with. Let's do an installation on the Windows box now.

The native Docker package can be run on 64-bit Windows 10 Professional or Enterprise. It uses the Windows 10 virtualization engine to virtualize the Linux kernel. This is the reason that the installation package does no longer contain the VirtualBox setup, as with the previous versions of Docker for Windows. The native application comes in a typical .msi installation package. If you run it, it will greet you with a friendly message, saying that it is going to live in your task bar tray, under the small whale icon, from now on:

The Docker's icon in the tray informs you about the Docker engine state. It also contains a small but useful context menu:

Let's explore the preferences settings and see what's available. The first tab, General, allows you to set Docker to run automatically when you log in. If you use Docker daily that may be the recommended setting. You can also mark to check for updates automatically and send usage statistics. Sending usage statistics will help the Docker team improve the tool in future versions; unless you have some mission critical, secure work to be done, I recommend turning this option on. This is a great way to contribute to future versions of this magnificent tool:

The second tab, Shared Drives, allows you to select the local Windows drives which will be available to the Docker containers you will be running:

We are going to cover Docker volumes in Chapter 2, Networking and Persistent Storage. Selecting a drive here means that you can map a directory from your local system and read that as a Windows host machine to your Docker container. The next preferences page, Advanced, allows us to make some restrictions on the Docker engine running on our Windows PC and also select the location of the virtual machine image with the Linux kernel:

The default values are usually good out of the box and unless you experience problems during the development process, I would recommend leaving them as they are. The Network lets you configure the way Docker works with the network, the same as subnet address and mask or DNS server. We are going to cover Docker networking in Chapter 2, Networking and Persistent Storage:

If you're behind a proxy in your network and would like Docker to access the Internet, you can set up the proxy settings in the Proxies tab:

The dialog is similar to what you find in other applications where you can define proxy settings. It can accept no proxy, system proxy settings, or manual settings (with a different proxy for HTPP and HTTPS communication). The next pane can be useful to configure the Docker daemon:

The Basic switch means that Docker uses the basic configuration. You can switch it to Advanced and provide a customized setting in a form of JSON structure. The Experimental features are the same as we have already mentioned during the Docker setup on macOS, this will be Checkpoint & Restore or enabling Docker graph driver plugins, for example. You can also specify a list of remote registries. Docker will be pulling images from insecure registries using just plain HTTP instead of HTTPS.

Using the Reset options on the last pane lets you restart or reset Docker to its factory settings:

Be aware though, that resetting Docker to its initial settings will also remove all images and containers currently present on your machine.

The Open Kitematic... option, which is also present in the Docker tray icon context menu, is a quick shortcut to launch Kitematic. If you do it for the first time and don't have Kitematic installed, Docker will ask if you would like to download it first:

That's it for installing Docker for Windows. It's a pretty painless process. As a last step of the installation process, let's check if Docker can be run from the command prompt, because it's probably the way you will be launching it in the future. Execute the following command in the command prompt or in the PowerShell:

docker run milkyway/java-hello-world  

As you can see on the previous screenshot, we have a Hello World message coming from the Java application started as a Docker container.