What is Docker?

What is Docker?

Containerization is one of the most recent technologies in the IT field. Its principle comes down to packing software in a common container, which simplifies its transfer and further unpacking. The most common tool for containerization is Docker. What are its features? What are the advantages? What recommendations should be followed when using it in order to fully experience and implement them?

General concept

First of all, you need to get acquainted with the containerization method in more detail. The container makes it possible to standardize the software deployment process, separating it from the existing, basic infrastructure. The program is launched in a separate environment, not associated with the OS, and does not affect it.

This approach simplifies the program development process; specialists do not need to think about a specific operating environment, the need for certain configurations and dependencies. Developers can fully focus on creating a program, pack all the settings necessary for correct operation into a container, without worrying about the inability to launch in an unsuitable OS.

Docker is a universal, functional, reliable platform in which you can develop, deliver, and launch container software. It not only allows you to work on creating containers, but also provides extensive capabilities for automating their activation, helps to keep the entire life cycle under control.

In general, the containerization method can be compared with virtualization, however, the concepts are not synonymous. Virtualization involves running a host on a hypervisor when another operating system is used inside one. Containerization is built on a different principle: the process is activated directly from the operating system kernel, without hardware virtualization, which reduces hardware requirements, ensures high performance with minimal processor load.

The platform was developed in 2008, but for the first 5 years it was used exclusively by the creator company, dotCloud. In 2013, free distribution began, the application immediately attracted the attention of developers, improvements began, and the creation of their own libraries.

Structure and operating principle

Docker makes it possible to implement virtualization at the operating system level, the kernel of which becomes the basis for the formation of a virtual environment. Structurally, the application consists of many components, each of which has its own functions and tasks:

• Host. OS in which Docker operates.
• Daemon. Service that manages all basic objects, from networks to containers.
• Client. A client that provides interaction between the user and the platform, processes commands, allows you to create containers, configure them.
• Image. This is an image that cannot be changed, which is the basis for deploying containers. An application that is being prepared for use must be packed into this image.
• Container. An application that has been deployed and successfully launched.
• Registry. A special storage for images.
• File. A file that contains instructions that, if followed, will help you correctly assemble the image.
• Compose. A multifunctional tool for interacting with several containers at once, creating, setting up, and configuring them.
• Desktop. A convenient GUI client that allows you to quickly understand all the capabilities of the platform and use the maximum of the available functions. There are versions for all popular operating systems, Linux, Mac, Windows.

Platform advantages

The main strengths of Docker can be presented as follows:

• Eliminating the complexity of dependencies and the working environment. In a container, you can place not only the main application, but also its dependencies, from configuration files to system utilities. This feature helps to transfer the program to a new infrastructure without unnecessary difficulties. This is important for developers who create a program in one environment, test and use it in others, where there may be no dependencies that provide functionality and the ability to run. With containers, such risks are excluded.
• High level of security. All processes packed in a container do not interact with the main operating system, which eliminates the risk of its damage, freezing, blocking other system processes.
• Ease of application deployment. The standard installation scheme for a new program involves activating scripts, adjusting files with settings, and other manipulations that complicate the process and take time. An inexperienced user may get confused and make a mistake that will render the program inoperable. The container method involves full automation of all actions, their execution in the strictly required order. The format is optimal, and when deploying an application on multiple servers at once, a specialist will not have to repeat identical manipulations several times.
• Approaching microservice architecture. Containers are optimally suited to it. This scheme is considered optimal, it implies that the application is divided into compact components, ideally independent, is the opposite of a monolithic architecture, all components of which are closely related. Microservice architecture accelerates the implementation of new functions, allows you to add new components without the risk of damaging the rest, disrupting the operation of the application.
• Comprehensive support. Developers have access to large selections of open source containers. If you can't find an image for a specific task, you can resort to the help of the community.
• Continuity of work. The platform allows you to use effective traffic management tools, thanks to which the application is updated automatically, without affecting the performance, functionality, and stability of the system.

On the issue of disadvantages

The platform is not without some disadvantages, however, they do not seem too serious, do not affect popularity. First of all, we are talking about the following points:

• Significant resource consumption. Docker plays the role of an auxiliary layer, which requires certain capacities and resources for confident operation. The user must immediately determine what is primary for him - convenience or load reduction. If the computer's performance is limited, it is more rational to stick to the traditional program installation scheme; for modern PCs, Docker is suitable.
• The need to use an orchestrator when interacting with large applications. The basic functionality of Docker is sufficient for working with several applications, however, it is not suitable if dozens and, especially, hundreds of services are used within one program. In such situations, you cannot do without orchestrators, for example, OpenShift or Kubernetes.
• Difficulties when working in Windows and Mac. The platform was developed for Linux, it is this operating system that allows you to 100% reveal its potential, use the maximum available functions without additional manipulations. On other OS, you will have to use virtual machines. This is not too difficult, however, it will require additional actions and computing resources.

Docker and data storage

A unique feature of Docker containers is their ephemerality. Simply put, they can be deleted, restarted, deactivated at the first need. All of these manipulations will lead to data loss, and therefore the program should initially be developed in such a way as not to depend on the information in the container.

This feature is ideal for software and services that do not need to save the results of their work. The simplest example is calculators that are only needed for calculations, and not for long-term storage. If there is a need for storage, you will have to use one of the following methods:

• Volumes. A volume is a special directory created directly by Docker, which allows you to solve the issue of storing information. A volume can be personal, working with a specific container, or shared - available to several at once. The storage location can be either the main computer, host, or remote servers, cloud services.
• Creating directories. The method involves creating a directory on the host and converting it into a container. It is reliable, but not very convenient, there are difficulties with backup, availability of information for several containers at once.
• Tmpfs. Tmpfs is a special file storage available exclusively on Linux. They are not suitable for long-term storage, stopping immediately leads to loss of information, however, they have an advantage - maximum access speed, due to which the container functions more stably and faster.

Practical use

Using Docker, you can effectively solve the following problems:

• Deployment of work environments and applications. The application can be transferred with literally a couple of commands. Deploying an operating system that will immediately have all the necessary settings is also a simple task.
• Launch isolation. The platform assumes that the application is launched separately from the system; failures caused by incompatibility with other software components are excluded.
• Resource control. Docker helps to rationally use available resources, accurately distribute them between different programs. Process isolation eliminates increased load on RAM and CPU.
• Security. Malicious code located in the container does not pose a threat to the host server. The main thing is the correct settings. Even with critical errors, all other services and services will remain operational.
• Rapid software development. Containerization is a method that makes programming require minimal time investment. The work of both individual programmers and entire teams is accelerated.
• Efficient interaction with complex systems and their scaling. Basic Docker functionality may not be enough for this, but orchestrators will come to the rescue of the developer.

Installing Docker

You can download the platform distribution from the official website. The installation algorithm on the Windows operating system is as follows:

• Open the downloaded distribution as administrator, start the installation.
• Reboot the computer after successful installation.
• Launch Docker Desktop.
• Accept all license agreements.
• Installing auxiliary WSL2 components, if necessary. They can be downloaded from the Microsoft website.

MacOS has a different algorithm:

• Selecting a distribution. It must match the processor that the computer is equipped with. Intel CPUs or proprietary Apple developments are used.
• Opening the “Docker.dmg” file, running the installation, moving the Docker icon to the program directory.
• Running the platform by double-clicking.
• Confirming acceptance of the license agreement, entering the password.
• Viewing or skipping instructions.

Working with a Docker image

The base image is the most important component of the platform, allowing you to use containerization technology. It stores processes and dependencies, without which the correct operation of the program would be impossible. The best option for a developer is to download a ready-made image from the library, there are many options, and you can easily select an image for a specific task.

Changing the original image creates layers that are available only for reading, so the final version consists of a whole complex of layers. The layered structure allows you to cancel changes if necessary, quickly solve problems with operability in case of erroneous actions.

An image can be thought of as a complex of layers available only for reading, a container is the same image, but with an additional upper layer, due to which the recording occurs. The main image file is manifest, where all the basic information is stored, links to layers, their volume, and other things that are required for stable operation.

Deploying an image does not imply any restrictions on the host or the number of times. The task can be completed in two ways:

• Interactive. The simplest, allowing the developer to change the environment at startup. To do this, use the command “docker run image_name: tag_name”.
• Dockerfile. A more complex scheme. Each image is associated with its own Dockerfile, in which you need to write the required commands, as well as exclude “extra” files that are not needed for a specific build, specifying them in .dockerignore. The command to create an image is “docker image build”.

Summing up

Docker is a very powerful platform that allows the developer to deploy the required service on any computer. In addition, it is an effective tool for testing a new program, delivering it to the server. Mastering it may seem difficult at first, but it won’t take much time even for a beginner, and in the long run it will save a lot of effort and resources.

Author of the article:

Editor-in-Chief

Danaev Almaz