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.

The official Docker logo in blue.

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.

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Our cloud platform manubes uses Docker technology to process production data in local networks with the help of edge nodes and securely transfer it to the cloud.

With innovative no-code design tools, manubes offers extensive options for an efficient monitoring, management and automation of production processes.

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.

Optimize your production with manubes

manubes offers a central platform for production data management, data visualization and workflow-based process automation.

Manufacturers gain access to a variety of innovative tools in order to quickly develop their own applications – tailored to their requirements.

FAQ

Other frequently asked questions about Docker

• How does Docker differ from a virtual machine (VM)?
• How do I install Docker on my system?
• What is the difference between a Docker image and a Docker container?
• What is Docker Hub and what is it used for?
• How do I start, stop, and remove a Docker container?
• How do I install and start the manubes Edge Node with Docker?
• Are there alternatives to Docker?

How does Docker differ from a virtual machine (VM)?

Both Docker and virtual machines are technologies used to virtualize resources. They use the physical resources of the host system, such as CPU and memory, to create a virtual environment for running software applications.

A Docker container contains the application code as well as all required configurations and dependencies needed to run it. Importantly, it does not contain or start its own operating system but instead utilizes the Kernel of the host system directly.

By contrast, virtual machines provide a complete, isolated computer system, including the hardware/kernel layer. They contain their own guest operating system, whereas Docker containers use the host operating system.

Docker containers are more lightweight than virtual machines, can be started and stopped more quickly and provide portability across different Linux platforms. With Docker Desktop, they can also be used on Windows and Mac.

Virtual machines provide stronger isolation and are often used to meet specific hardware and operating system requirements since they provide their own operating system.

How do I install Docker on my system?

To use Docker containers, the Docker Engine is required. It can be installed directly on various Linux distributions.

Alternatively, Docker Desktop can be installed on Linux, Windows or Mac systems. Docker Desktop not only includes the Docker Engine but also provides a graphical user interface for managing containers.

What is the difference between a Docker image and a Docker container?

A Docker image is a read-only template that contains application code, dependencies and configurations. An image is used to start one or more instances of a Docker container based on that image.

A Docker container is a running or stopped instance of a Docker image. The container has its own state, including changes to the file system, running processes and temporary files. These changes do not affect the underlying Docker image.

What is Docker Hub and where is it used?

Docker Hub is an online platform for storing, managing and sharing Docker images, both privately within organizations and publicly.

The platform provides more than 10 million Docker images across various categories.

How do I start, stop and remove a Docker container?

Docker containers can be started and stopped by entering commands in the command line.

The docker run command starts a Docker container from a Docker image. Various options and commands can be specified.

Options affect the properties of the container, such as resource limits and IP/MAC addresses. Commands are instructions that are executed inside the container after it starts.

In the example shown, a Docker container named “test” is created from the Docker image “my-image”:

The command docker start starts one or more stopped Docker containers.

The command docker stop stops one or more Docker containers.

The command docker rm removes a stopped Docker container.

How do I install and start the manubes Edge Node via Docker?

Our cloud platform manubes uses edge components to enable secure, bidirectional data exchange with machines, devices and software systems across different locations.

Edge Nodes run inside Docker containers on local devices, where they provide data processing capabilities and enable secure access to local systems.

After adding an Edge Node in manubes, users can retrieve the command required to start the Docker container. The Docker image is downloaded automatically when the command is executed.

Alternatively, the installation can be performed using the container management solution Portainer.

On Windows systems, manubes Edge Nodes can be easily downloaded and installed using the “Windows Service” option.

Are there alternatives to Docker?

In addition to Docker, there are other tools for container virtualization. One of the best-known alternatives is Podman, another open-source container engine.

Podman takes a different technical approach from Docker: While Docker relies on a central, continuously running daemon process (the Docker daemon), Podman works in a “daemonless” manner, meaning it does not require such a background process. Instead, container management is handled by processes that are created when the respective container is started.

Despite these differences, Podman is largely compatible with Docker. Many Docker commands work the same way with Podman because Podman’s command-line interface (CLI) is modeled on Docker’s. Docker images and Dockerfiles can also generally be used with Podman without modification.

Other alternatives to Docker include containerd and CRI-O, although these are more commonly used in the background of container orchestration solutions such as Kubernetes.