Docker is a tool for developing, delivering, and running applications. It represents a private type of virtualization known as containerization.
Virtualization is the provision of a set of computing resources, or their logical combination, abstracted from the hardware implementation and ensuring logical isolation of computing processes running on a single physical resource.
In simpler terms, virtualization allows you to emulate the functioning of any software, including on your computer, to run other operating systems, emulate network equipment, and deploy multiple operating systems without needing to reinstall the primary one.
Virtualization can be divided into:
- Software-based virtualization, where virtualization software (hypervisor) is installed on the operating system, and
- Hardware-based virtualization, where the hypervisor is installed directly on the computer (e.g., Hyper-V, VMware ESX/ESXi).
Containerization allows you to run a specific application without deploying a full operating system for a virtual machine. It requires only the minimum necessary resources to launch an application, significantly saving computing resources.
Advantages of Containerization
- Ease of Deployment: Any application can easily be packaged into a container, deployed, and run on any computer.
- Resource Efficiency: Containerization doesn’t require virtualizing the entire OS, saving disk space and memory. Only the host kernel is used at the processor level, allowing more containers (virtual applications) to run on a single server.
- Quick Deployment: Templates allow creating a configured OS image with the required software once, which can be reused “out of the box” or downloaded and tested as needed.
- Security: Containerization isolates applications in different virtual environments, so the operation of one application doesn’t affect another or access its data.
What Problems Does Docker Solve?
Docker can be installed on Windows, Linux, or macOS and allows downloading any image (OS, programming languages, or required server environments) from the Docker Hub repository (https://hub.docker.com/, in the Explore section).
For example, code written in a Dockerfile (used to describe the required environment for deployment):
This code commands Docker to download PHP version 7.2 with Apache server support, eliminating the need for additional Apache installation and configuration.
Docker also enables creating a container from an image, testing and studying downloaded programming languages without installing or configuring them on your computer. You can pack the written code into a container and publish it on Docker Hub, allowing anyone with Docker to download and run it without needing further installation.
Why Is Docker Listed in Every Job Posting?
Docker is an excellent tool for Continuous Deployment (CD), widely used in commercial companies to speed up product updates. Using Docker significantly reduces deployment and environment setup time, including for testing purposes. Currently, around 90% of IT companies use Docker or similar tools in their development processes.
What Docker Skills Are Needed for a Junior Developer Position?
A beginner programmer should understand how Docker works, know how to download images, deploy and run containers, create projects based on them, write Dockerfiles (which describe the environment Docker needs to deploy a project, including programming languages and libraries) and Docker Compose files (which describe configurations for large projects involving multiple images).