What is Docker?

Definition

What is Docker?

Docker is an open source software for the container virtualization of applications that was first published in 2013.

With Docker, software applications can be developed, deployed and run in isolated containers.

This offers various benefits: Containerized programs can be easily shared and consistently tested, installed and executed on different operating systems.

For this reason, Docker has quickly become an important tool for many software developers. Many well-known applications and platforms such as WordPress, GitLab and MongoDB support or use Docker technology.

Explanation

How does Docker work?

There are various versions of Docker and ways to use the technology.

Docker Engine for Linux, also known as Docker Community Edition (Docker CE), can be installed for various Linux distributions and allows the execution of Docker containers. Instructions can be found in the Docker documentation.

Docker Desktop is a program with a graphical user interface that can be downloaded and installed on Windows, Linux and Mac systems. Users can create, run and manage their own containers using Docker Desktop.

Docker Desktop can be downloaded from the Docker website. Downloads for Windows, Linux and Mac are available there.

Docker can also be used to install and run software on smaller (Linux-based) devices. You can find out more about this in the section „Where is Docker being used?“.

Docker Hub is an online platform for publishing and sharing Docker images (see „What is a Docker Image?“) and repositories. Docker images can be shared publicly, privately or in-house via Docker Hub.

Below we explain the most important concepts and terms related to Docker.

What is a Docker container?

A Docker container is an isolated environment for code. The container has its own (isolated) file system and thus enables the execution of code or software.

Docker containers can communicate with each other, allowing individual containers to be linked together in a targeted manner. This enables the execution of so-called “microservices” in several, often very large numbers of containers, which together form a complete application.

Docker containers share the resources of the host computer on which they run and require a Linux kernel. However, with the help of certain virtualization software / Docker Desktop, they can also be run on Windows and Mac.

What is a Docker image?

A Docker image is the representation of a Docker container. It contains the code for the Docker container and its dependencies and can be used to start one or more instances of the container. Docker images are easy to share.

Example: Developer A uses Docker Desktop to create an application in a Docker container. She saves an image of the container and makes it available online. Developer B downloads the Docker image and executes it to start a container with the application created by A.

A Docker image consists of several layers. A new layer is created each time a change is made (see „Version management with Docker“).

What is a Dockerfile?

A Dockerfile defines the steps for creating a Docker image. It is a text file with instructions that are applied one after the other when the Dockerfile is executed and add new layers to the Docker image.

The creation of a Docker image from a Dockerfile is referred to as the build process.

Version management with Docker

A Docker image consists of several layers. Each time the image is changed, a new layer is created to show the changes. These layers are read-only and cannot be manipulated.

The layers can be used to track the differences between two versions of an image and the history of an image.

Advantages

What are the benefits of using Docker?

Container virtualization with Docker offers various advantages over other development and deployment environments:

Portability and consistency:
Docker containers are not only portable, but also consistent across different environments. Developers can create and test containers locally and then deploy them to different production environments without having to worry about incompatibilities or configuration differences. This helps to create a consistent development, test and production environment.

Efficient use of resources:
Docker optimizes resource usage by sharing the operating system kernel. Unlike virtualization technologies that require separate operating system instances for each virtual machine, Docker containers share the host operating system kernel.

Rapid deployment:
Docker enables rapid deployment of applications. Docker containers can be started from a Docker image within seconds.

Scalability:
Docker facilitates the horizontal scaling of applications, as additional containers can be easily added when workloads increase.

Support for microservice architectures:
Docker offers the option of running components of an application, known as microservices, separately from each other. The presence of multiple identical services (redundancy) ensures reliability. The scalability of the architecture can be achieved by flexibly adding or removing containers. Targeted monitoring, updates and repairs are also possible.

Use Cases

Where is Docker being used?

The most important areas of application for Docker technology include DevOps environments, cloud computing and edge computing.

Docker and DevOps

The term DevOps covers various methods, tools and approaches that enable close collaboration between software development (Development) and IT operations (Operations). The aim is to make the development process more efficient and improve the quality of applications.

Docker is relevant for DevOps for various reasons: The portability of Docker containers means that applications can be tested and executed in different environments and therefore deployed quickly. Errors that occur due to environmental differences are minimized with Docker.

The reliability and scalability of Docker-based microservice architectures also support efficient IT operations.

Docker and cloud computing

Large cloud environments such as Amazon Web Services, Microsoft Azure or IBM Cloud offer support for Docker. This allows users of the cloud infrastructure to run their containerized applications in the cloud and, depending on the platform, manage them with additional advanced tools.

Docker and edge computing

Docker containers can be used on (Linux-based) edge devices and in distributed networks to run applications and services close to the data sources or end users.

Containerization with Docker makes it possible to decouple the development and target environment of applications. Not only can programs be rolled out consistently on different devices with Docker, but version control and maintenance are also made easier. Special solutions such as Portainer have been developed for use cases in which a large number of containers need to be installed, managed, updated and monitored.

Our cloud platform manubes also uses Docker containers to run edge nodes on various target systems. These make it possible to process industrial data locally and transfer it securely to the manubes cloud environment.