Learning Docker

Chapter 1. Getting Started with Docker

These days, Docker technology is gaining more market and more mind shares among information technology (IT) professionals across the globe. In this chapter, we would like to shed more light on Docker, and show why it is being touted as the next best thing for the impending cloud IT era. In order to make this book relevant to software engineers, we have listed the steps needed for crafting highly usable application-aware containers, registering them in a public registry repository, and then deploying them in multiple IT environments (on-premises as well as off-premises). In this book, we have clearly explained the prerequisites and the most important details of Docker, with the help of all the education and experiences that we could gain through a series of careful implementations of several useful Docker containers in different systems. For doing this, we used our own laptops as well as a few leading public Cloud Service Providers (CSP).

We would like to introduce you to the practical side of Docker for the game-changing Docker-inspired containerization movement.

In this chapter, we will cover the following topics:

An introduction to Docker
Docker on Linux
Differentiating between containerization and virtualization
Installing the Docker engine
Understanding the Docker setup
Downloading the first image
Running the first container
Running a Docker container on Amazon Web Services (AWS)
Troubleshooting the Docker containers

An introduction to Docker

Due to its overwhelming usage across industry verticals, the IT domain has been stuffed with many new and pathbreaking technologies used not only for bringing in more decisive automation but also for overcoming existing complexities. Virtualization has set the goal of bringing forth IT infrastructure optimization and portability. However, virtualization technology has serious drawbacks, such as performance degradation due to the heavyweight nature of virtual machines (VM), the lack of application portability, slowness in provisioning of IT resources, and so on. Therefore, the IT industry has been steadily embarking on a Docker-inspired containerization journey. The Docker initiative has been specifically designed for making the containerization paradigm easier to grasp and use. Docker enables the containerization process to be accomplished in a risk-free and accelerated fashion.

Precisely speaking, Docker is an open source containerization engine, which automates the packaging, shipping, and deployment of any software applications that are presented as lightweight, portable, and self-sufficient containers, that will run virtually anywhere.

A Docker container is a software bucket comprising everything necessary to run the software independently. There can be multiple Docker containers in a single machine and containers are completely isolated from one another as well as from the host machine.

In other words, a Docker container includes a software component along with all of its dependencies (binaries, libraries, configuration files, scripts, jars, and so on). Therefore, the Docker containers could be fluently run on x64 Linux kernel supporting namespaces, control groups, and file systems, such as Another Union File System (AUFS). However, as indicated in this chapter, there are pragmatic workarounds for running Docker on other mainstream operating systems, such as Windows, Mac, and so on. The Docker container has its own process space and network interface. It can also run things as root, and have its own /sbin/init, which can be different from the host machines'.

In a nutshell, the Docker solution lets us quickly assemble composite, enterprise-scale, and business-critical applications. For doing this, we can use different and distributed software components: Containers eliminate the friction that comes with shipping code to distant locations. Docker also lets us test the code and then deploy it in production as fast as possible. The Docker solution primarily consists of the following components:

The Docker engine
The Docker Hub

The Docker engine is for enabling the realization of purpose-specific as well as generic Docker containers. The Docker Hub is a fast-growing repository of the Docker images that can be combined in different ways for producing publicly findable, network-accessible, and widely usable containers.

Differentiating between containerization and virtualization

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:

Virtual Machines (VMs)	Containers
Represents hardware-level virtualization	Represents operating system virtualization
Heavyweight	Lightweight
Slow provisioning	Real-time provisioning and scalability
Limited performance	Native performance
Fully isolated and hence more secure	Process-level isolation and hence less secure

The convergence of containerization and virtualization

A hybrid model, having features from both the virtual machines and that of containers, is being developed. It is the emergence of system containers, as illustrated in the preceding right-hand-side diagram. Traditional hypervisors, which implicitly represent hardware virtualization, directly secure the environment with the help of the server hardware. That is, VMs are completely isolated from the other VMs as well as from the underlying system. But for containers, this isolation happens at the process level and hence, they are liable for any kind of security incursion. Furthermore, some vital features that are available in the VMs are not available in the containers. For instance, there is no support for SSH, TTY, and the other security functionalities in the containers. On the other hand, VMs are resource-hungry and hence, their performance gets substantially degraded. Indeed, in containerization parlance, the overhead of a classic hypervisor and a guest operating system will be eliminated to achieve bare metal performance. Therefore, a few VMs can be provisioned and made available to work on a single machine. Thus, on one hand, we have the fully isolated VMs with average performance and on the other side, we have the containers that lack some of the key features, but are blessed with high performance. Having understood the ensuing needs, product vendors are working on system containers. The objective of this new initiative is to provide full system containers with the performance that you would expect from bare metal servers, but with the experience of virtual machines. The system containers in the preceding right-hand-side diagram represent the convergence of two important concepts (virtualization and containerization) for smarter IT. We will hear and read more about this blending in the future.

Containerization technologies

Having recognized the role and the relevance of the containerization paradigm for IT infrastructure augmentation and acceleration, a few technologies that leverage the unique and decisive impacts of the containerization idea have come into existence and they have been enumerated as follows:

LXC (Linux Containers): This is the father of all kinds of containers and it represents an operating-system-level virtualization environment for running multiple isolated Linux systems (containers) on a single Linux machine.
The article LXC on the Wikipedia website states that:
"The Linux kernel provides the cgroups functionality that allows limitation and prioritization of resources (CPU, memory, block I/O, network, etc.) without the need for starting any virtual machines, and namespace isolation functionality that allows complete isolation of an applications' view of the operating environment, including process trees, networking, user IDs and mounted file systems."
You can get more information from http://en.wikipedia.org/wiki/LXC.
OpenVZ: This is an OS-level virtualization technology based on the Linux kernel and the operating system. OpenVZ allows a physical server to run multiple isolated operating system instances, called containers, virtual private servers (VPSs), or virtual environments (VEs).
The FreeBSD jail: This is a mechanism that implements an OS-level virtualization, which lets the administrators partition a FreeBSD-based computer system into several independent mini-systems called jails.
The AIX Workload partitions (WPARs): These are the software implementations of the OS-level virtualization technology, which provide application environment isolation and resource control.
Solaris Containers (including Solaris Zones): This is an implementation of the OS-level virtualization technology for the x86 and SPARC systems. A Solaris Container is a combination of the system resource controls and boundary separation provided by zones. Zones act as completely isolated virtual servers within a single operating system instance.

In this book, considering the surging popularity and the mass adoption happening to Docker, we have chosen to dig deeper, dwell in detail on the Docker platform, the one-stop solution for the simplified and streamlined containerization movement.

Installing the Docker engine

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.

Note

We have chosen the Ubuntu Trusty 14.04 (LTS) (64-bit) Linux distribution for all practical purposes.

Installing from the Ubuntu package repository

This section explains the steps involved in installing the Docker engine from the Ubuntu package repository in detail. At the time of writing this book, the Ubuntu repository had packaged Docker 1.0.1, whereas the latest version of Docker was 1.5. We strongly recommend installing Docker version 1.5 or greater by using any one of the methods described in the next section.

However, if for any reason you have to install the Ubuntu packaged version, then please follow the steps described here:

The best practice for installing the Ubuntu packaged version is to begin the installation process by resynchronizing with the Ubuntu package repository. This step will essentially update the package repository to the latest published packages, thus we will ensure that we always get the latest published version by using the command shown here:
```
$ sudo apt-get update
```
Tip
Downloading the example code
You can download the example code files from your account at http://www.packtpub.com for all the Packt Publishing books you have purchased. If you purchased this book elsewhere, you can visit http://www.packtpub.com/support and register to have the files e-mailed directly to you.
Kick-start the installation by using the following command. This setup will install the Docker engine along with a few more support files, and it will also start the docker service instantaneously:
```
$ sudo apt-get install -y docker.io
```
Note
The Docker package is called docker.io because an older version of the Ubuntu package was called docker. As a result, all the files with the name docker are installed as docker.io.
Examples are /usr/bin/docker.io and /etc/bash_completion.d/docker.io.
For your convenience, you can create a soft link for docker.io called docker. This will enable you to execute Docker commands as docker instead of docker.io. You can do this by using the following command:
```
$ sudo ln -sf /usr/bin/docker.io /usr/local/bin/docker
```
Note
The official Ubuntu package does not come with the latest stable version of docker.

Installing the latest Docker using docker.io script

The official distributions might not package the latest version of Docker. In such a case, you can install the latest version of Docker either manually or by using the automated scripts provided by the Docker community.

For installing the latest version of Docker manually, follow these steps:

Add the Docker release tool's repository path to your APT sources, as shown here:

$ sudo sh -c "echo deb https://get.docker.io/ubuntu \
    docker main > /etc/apt/sources.list.d/docker.list"

Import the Docker release tool's public key by running the following command:

$ sudo apt-key adv --keyserver \
    hkp://keyserver.ubuntu.com:80 --recv-keys \
    36A1D7869245C8950F966E92D8576A8BA88D21E9

Resynchronize with the package repository by using the command shown here:
```
$ sudo apt-get update
```
Install docker and then start the docker service.
```
$ sudo apt-get install -y lxc-docker
```

Note

The lxc-docker command will install the Docker image using the name docker.

The Docker community has taken a step forward by hiding these details in an automated install script. This script enables the installation of Docker on most of the popular Linux distributions, either through the curl command or through the wget command, as shown here:

For curl command:

$ sudo curl -sSL https://get.docker.io/ | sh

For wget command:

$ sudo wget -qO- https://get.docker.io/ | sh

Note

The preceding automated script approach enforces AUFS as the underlying Docker file system. This script probes the AUFS driver, and then installs it automatically if it is not found in the system. In addition, it also conducts some basic tests upon installation for verifying the sanity.

Understanding the Docker setup

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 version
The client API version
The server version
The server API version

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.

Client server communication

On Linux installations, Docker is usually programmed for carrying out server-client communication by using the Unix socket (/var/run/docker.sock). Docker also has an IANA registered port, which is 2375. However, for security reasons, this port is not enabled by default.

Running a Docker container on Amazon Web Services

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 (only available in preview mode at the time of writing this book)
Docker deployment by using the Amazon Elastic Beans services

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:

A single container that supports Elastic Beanstalk by using a console. Currently, it supports the PHP and Python applications.
A single container that supports Elastic Beanstalk by using a command line tool called eb. It supports the same PHP and Python applications.
Use of multiple container environments by using Elastic beanstalk.

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:

Log in to the AWS Elastic Beanstalk console by using this https://console.aws.amazon.com/elasticbeanstalk/ URL.
Select a region where you want to deploy your application, as shown here:
Select the Docker option, which is in the drop down menu, and then click on Launch Now. The next screen will be shown after a few minutes, as shown here:
Now, click on the URL that is next to Default-Environment (Default-Environment-pjgerbmmjm.elasticbeanstalk.com), as shown here:

Carles Aug 13, 2015

Either if you are a Developer or a System Administrator, Docker is about to be a must know and must have in your daily toolbox.When a new technology arises and you want to get savvy on it, you can choose between two roads: diving into hundreds of not so well documented and often outdated on-line tutorials or going for the right way and choose a good book like this that guides and helps you in the process. This book it's written with this kind of scenario in mind, going straight to the point that matters, in order to help and speed up your learning curve.On chapter 1 you'll learn what it's docker and how can you benefit from using it on your daily work. If you are a developer who wants to start using this technology the book guides you through a series of chapters that discuses all you need to know to get confident with it (chapters 1 to 4). In the other hand if you are a system administrator, once you know the basis from the 4th first chapters, you only need to keep walking your way across the chapter 5 to get all you need to know to deploy and maintain you own private Docker infrastructure.From that point both developers and System Administrators still have chapters 6 to 11 to get deeper knowledge of more areas of expertise regarding Docker ecosystem.Summarizing, if you buy this book you'll get a very comprehensive and easy way to master Docker technology in a very short time.

Amazon Verified review

Venkatesh Bhat Aug 15, 2015

This is a great reference book for cloud developers, from novice to expert. It covers nearly all features with docker container, followed by a hands-on example.It effectively demonstrates the advantages of running multiple containers within a virtual machine instead of spinning up a virtual machine for every application.The book is well written in simple terms and could be easily used for preparing presentation about docker features.Most recommended for container enthusiasts.

incognito.programmer Aug 13, 2015

I truly enjoyed this book. Pretty easy reading for the most part. After reading this book I went from 0 to being able to have an educated conversation with others about docker, and dare I say it maybe get a container or two running! (Haven't done it yet, as I haven't had the time).The only knock from me on this book is the part about security. I felt like that chapter could've been better.

Fran Oct 11, 2016

Is not bad, direct, no verbose, handy, easy to find all the topics and doubts. Maybe I miss a little some more examples with the docker run command line, because to be honest just appear a couple of times, which is quite annoying, but ok.

Jascha Casadio Nov 22, 2015

At the beginning of November 2015, Docker 1.9 was released and with it multi-host networking was introduced. At the same time, Swarm finally reached a stable state that guaranteed it the label of production-ready. The DockerCon that took place in Barcelona was a success, confirming 2015 has been a great year for that blue whale. The strong impact containers had on the IT world is reflected on the one hand by the many companies investing on it, and on the other by the humongous amount of blog posts and books dedicated to it. In a scenario where some must-have title has already been released (see the bottom for suggested titles), Learning Docker places itself as an introductory text that targets professionals and enthusiasts interested in getting a quick taste of this new technology.Docker is one of those technologies that I am particularly interested in. I have been reading a lot about it, from the official documentation up to blogs, passing through that horde of books that made it up to the Amazon’s shelves. Getting through these 200 pages took me less than two days, mainly because none of the topics covered was new to me. But let’s dive into it!The very first thing that I have noticed about this title is the complete lack of background about what Docker is and, mainly, how it works under the hood. I did not find a single paragraph describing what a union mount is. Union mounts are one of the many key concepts of Docker that are not explained at all. Another concept that is not explained at all is, for example, that of the build context. Mind, the term build context appears all over the book, but the reader is not told what it is. The examples that show how to build an image use it without making it clear that the build context is that lone dot at the very end of the command. Concepts such as name spaces and cgroups are, instead, briefly described at the very end of the book, in the chapter dedicated to security.Another thing I did not appreciate much is the quality of the diagrams used to present the concepts being explained. They are colorful yes, but they could have been definitely better. But diagrams apart, do we really need screenshots to guide us through the signup form of the Docker Hub?The examples presented by the authors are very simple. Throughout the book there is not a single real-world example, nothing that gets beyond the containers’ equivalent of an Hello World! in C. Still, this is a very beginners’ book. This also means that topics such as Kubernetes or Mesos are not touched at all.Tying it all up, a very beginners’ book that I did not like but that someone completely new to the subject could find easy to read to get started. Still, the book can’t keep up with the competition: beginners should prefer passing through each and every page of the official documentation and, optionally, Turnbull’s The Docker Book.Suggested readings:The Docker Book: an user friendly, concise introduction to Docker. While it does not cover many advanced topics, it’s by far the best covering the basics.Docker Hands on: while not helpful to beginners, it offers the reader many advanced topics that can’t be found anywhere else.Docker: Up and Running: a very good text that focuses on advanced topics, mainly containers security.As usual, you can find more reviews on my personal blog: http://books.lostinmalloc.com. Feel free to pass by and share your thoughts!

Learning Docker: Optimize the power of Docker to run your applications quickly and easily

What do you get with a Packt Subscription?

Learning Docker

Chapter 1. Getting Started with Docker

An introduction to Docker

Docker on Linux

Differentiating between containerization and virtualization

The convergence of containerization and virtualization

Containerization technologies

Installing the Docker engine

Note

Installing from the Ubuntu package repository

Tip

Note

Note

Installing the latest Docker using docker.io script

Note

Note

Understanding the Docker setup

Client server communication

Downloading the first Docker image

Running the first Docker container

Running a Docker container on Amazon Web Services

Troubleshooting

Summary

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Learning Docker: Optimize the power of Docker to run your applications quickly and easily

What do you get with a Packt Subscription?

Tip

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Description

Who is this book for?

What you will learn

Product Details

What do you get with a Packt Subscription?

Product Details

Packt Subscriptions

Frequently bought together

Table of Contents

Recommendations for you

Customer reviews

People who bought this also bought

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