Docker basics

Containerization vs Virtualization – An introduction to Docker

Pethuru Raj, Jeeva S. Chelladhurai, Vinod Singh
docker containers
Container image via Shutterstock

As Docker technology gains more popularity among IT professionals, it’s becoming increasingly important for programmers to grasp the basics of containerization. Here we learn why Docker is at the centre of cloud IT era hype, as well as the difference between containerization and virtualization.

This introduction to Docker is taken from the Packt title Learning Docker. JAXenter readers can get a 50% discount using the following code: LEDOC50

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, 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.

Docker on Linux

docker on linux

Figure 1: Docker on Linux

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 figure 1.

This illustration 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.

Containerization vs 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.

containers virtual

Figure 2: Containerization vs Virtualization

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 (figure 2) 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:

docker table

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 on Wikipedia.

  • 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.
learning docker

Pethuru Raj, Jeeva S. Chelladhurai, Vinod Singh

Pethuru Raj, PhD, works as a cloud architect at the IBM Global Cloud Center of Excellence (CoE) in Bangalore, India.Jeeva S. Chelladhurai has been working as a technical project manager at the IBM Global Cloud Center of Excellence (CoE) in India for the last 8 years. He has more than 18 years of experience in the IT industry. Vinod Singh is a lead architect for IBM’s cloud computing offerings. He has more than 18 years of experience in the cloud computing, networking, and data communication domains. You can get the full copy of Learning Docker on

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