Suppose that we want to directly run the containers on a Linux machine. The Docker engine produces, monitors, and manages multiple containers as illustrated in the following diagram:

The preceding diagram vividly illustrates how future IT systems would have hundreds of application-aware containers, which would innately be capable of facilitating their seamless integration and orchestration for deriving modular applications (business, social, mobile, analytical, and embedded solutions). These contained applications could fluently run on converged, federated, virtualized, shared, dedicated, and automated infrastructures.

It is pertinent, and paramount to extract and expound the game-changing advantages of the Docker-inspired containerization movement over the widely used and fully matured virtualization paradigm. In the containerization paradigm, strategically sound optimizations have been accomplished through a few crucial and well-defined rationalizations and the insightful sharing of the compute resources. Some of the innate and hitherto underutilized capabilities of the Linux kernel have been rediscovered. These capabilities have been rewarded for bringing in much-wanted automation and acceleration, which will enable the fledgling containerization idea to reach greater heights in the days ahead, especially those of the cloud era. The noteworthy business and technical advantages of these include the bare metal-scale performance, real-time scalability, higher availability, and so on. All the unwanted bulges and flab are being sagaciously eliminated to speed up the roll-out of hundreds of application containers in seconds and to reduce the time taken for marketing and valuing in a cost-effective fashion. The following diagram on the left-hand side depicts the virtualization aspect, whereas the diagram on the right-hand side vividly illustrates the simplifications that are being achieved in the containers:

The following table gives a direct comparison between virtual machines and containers:

The Docker engine is built on top of the Linux kernel and it extensively leverages its features. Therefore, at this point in time, the Docker engine can only be directly run on Linux OS distributions. Nonetheless, the Docker engine could be run on the Mac and Microsoft Windows operating systems by using the lightweight Linux VMs with the help of adapters, such as Boot2Docker. Due to the surging growing of Docker, it is now being packaged by all major Linux distributions so that they can retain their loyal users as well as attract new users. You can install the Docker engine by using the corresponding packaging tool of the Linux distribution; for example, by using the apt-get command for Debian and Ubuntu, and the yum command for RedHat, Fedora, and CentOS.

It's important to understand Docker's components and their versions, storage, execution drivers, file locations, and so on. Incidentally, the quest for understanding the Docker setup would also reveal whether the installation was successful or not. You can accomplish this by using two docker subcommands, namely docker version, and docker info.

Let's start our docker journey with the docker version subcommand, as shown here:

$ sudo docker version
Client version: 1.5.0
Client API version: 1.17
Go version (client): go1.4.1
Git commit (client): a8a31ef
OS/Arch (client): linux/amd64
Server version: 1.5.0
Server API version: 1.17
Go version (server): go1.4.1
Git commit (server): a8a31ef

Although the docker version subcommand lists many lines of text, as a Docker user, you should know what these following output lines mean:

The client and server versions that have been considered here are 1.5.0 and the client API and the server API, versions 1.17.

If we dissect the internals of the docker version subcommand, then it will first list the client-related information that is stored locally. Subsequently, it will make a REST API call to the server over HTTP to obtain the server-related details.

Let's learn more about the Docker environment using the docker info subcommand:

$ sudo docker -D info
Containers: 0
Images: 0
Storage Driver: aufs
 Root Dir: /var/lib/docker/aufs
 Backing Filesystem: extfs
 Dirs: 0
Execution Driver: native-0.2
Kernel Version: 3.13.0-45-generic
Operating System: Ubuntu 14.04.1 LTS
CPUs: 4
Total Memory: 3.908 GiB
Name: dockerhost
ID: ZNXR:QQSY:IGKJ:ZLYU:G4P7:AXVC:2KAJ:A3Q5:YCRQ:IJD3:7RON:IJ6Y
Debug mode (server): false
Debug mode (client): true
Fds: 10
Goroutines: 14
EventsListeners: 0
Init Path: /usr/bin/docker
Docker Root Dir: /var/lib/docker
WARNING: No swap limit support

As you can see in the output of a freshly installed Docker engine, the number of Containers and Images is invariably nil. The Storage Driver has been set up as aufs, and the directory has been given the /var/lib/docker/aufs location. The Execution Driver has been set to the native mode. This command also lists details, such as the Kernel Version, the Operating System, the number of CPUs, the Total Memory, and Name, the new Docker hostname.

Having installed the Docker engine successfully, the next logical step is to download the images from the Docker registry. The Docker registry is an application repository, which hosts a range of applications that vary between basic Linux images and advanced applications. The docker pull subcommand is used for downloading any number of images from the registry. In this section, we will download a tiny version of Linux called the busybox image by using the following command:

$ sudo docker pull busybox
511136ea3c5a: Pull complete
df7546f9f060: Pull complete
ea13149945cb: Pull complete
4986bf8c1536: Pull complete
busybox:latest: The image you are pulling has been verified. Important: image verification is a tech preview feature and should not be relied on to provide security.
Status: Downloaded newer image for busybox:latest

Once the images have been downloaded, they can be verified by using the docker images subcommand, as shown here:

$ sudo docker images
REPOSITORY    TAG     IMAGE ID         CREATED      VIRTUAL SIZE
busybox       latest  4986bf8c1536     12 weeks ago 2.433 MB

Now, you can start your first Docker container. It is standard practice to start with the basic Hello World! application. In the following example, we will echo Hello World! by using a busybox image, which we have already downloaded, as shown here:

$ sudo docker run busybox echo "Hello World!"
"Hello World!"

Cool, isn't it? You have set up your first Docker container in no time. In the preceding example, the docker run subcommand has been used for creating a container and for printing Hello World! by using the echo command.

Amazon Web Services (AWS) announced the availability of Docker containers at the beginning of 2014, as a part of its Elastic Beanstalk offering. At the end of 2014, they revolutionized Docker deployment and provided the users with options shown here for running Docker containers:

The Amazon EC2 container service lets you start and stop the container-enabled applications with the help of simple API calls. AWS has introduced the concept of a cluster for viewing the state of your containers. You can view the tasks from a centralized service, and it gives you access to many familiar Amazon EC2 features, such as the security groups, the EBS volumes and the IAM roles.

Please note that this service is still not available in the AWS console. You need to install AWS CLI on your machine to deploy, run, and access this service.

The AWS Elastic Beanstalk service supports the following:

Currently, AWS supports the latest Docker version, which is 1.5.

This section provides a step-by-step process to deploy a sample application on a Docker container running on AWS Elastic Beanstalk.The following are the steps of deployment:

Most of the time, you will not encounter any issues when installing Docker. However, unplanned failures might occur. Therefore, it is necessary to discuss prominent troubleshooting techniques and tips. Let's begin by discussing the troubleshooting knowhow in this section. The first tip is that the running status of Docker should be checked by using the following command:

$ sudo service docker status

However, if Docker has been installed by using the Ubuntu package, then you will have to use docker.io as the service name. If the docker service is running, then this command will print the status as start/running along with its process ID.

If you are still experiencing issues with the Docker setup, then you could open the Docker log by using the /var/log/upstart/docker.log file for further investigation.

Containerization is going to be a dominant and decisive paradigm for the enterprise as well as cloud IT environments in the future because of its hitherto unforeseen automation and acceleration capabilities. There are several mechanisms in place for taking the containerization movement to greater heights. However, Docker has zoomed ahead of everyone in this hot race, and it has successfully decimated the previously-elucidated barriers.

In this chapter, we have exclusively concentrated on the practical side of Docker for giving you a head start in learning about the most promising technology. We have listed the appropriate steps and tips for effortlessly installing the Docker engine in different environments, for leveraging and for building, installing, and running a few sample Docker containers, both in local as well as remote environments. We will dive deep into the world of Docker and dig deeper to extract and share tactically and strategically sound information with you in the ensuing chapters. Please read on to gain the required knowledge about advanced topics, such as container integration, orchestration, management, governance, security, and so on, through the Docker engine. We will also discuss a bevy of third-party tools.