What is Docker?
Docker enables you to create, deploy and manage virtual application containers. Launched in 2013, this technology quickly gained traction in the development sector, as it allowed developers to work with unprecedented flexibility and portability. Find out more about Docker in this article.
What is a container?
Docker is now so popular that the terms “Docker” and “containers” are often used interchangeably. However, container technologies had been available for years, if not decades, before Docker became publicly available in 2013.
But let's get right to the point: what is Docker? Docker is an open-source software platform used to create, deploy and manage virtualised application containers on a common OS (operating system). It also comes with an ecosystem of allied tools.
Docker container technology was launched in 2013. At the time, Docker Inc. was created to support a commercial edition of container management software, as well as act as the primary sponsor of an open-source version.
Docker offers software developers a faster and more efficient way to develop and testcontainerised portions of a global software application, allowing them to develop multiple software programs at the same time.
Each container contains all the elements needed to build a software component and ensures that it will be developed, tested and deployed smoothly. Docker enables portability for when these packaged containers are transferred to different servers or environments.
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A central element of Docker is the use of Docker images: immutable files that contain all the elements required to run an application, making it easier to deploy and distribute applications across a variety of computing environments.
How does Docker work?
Docker packages, provisions and runs containers. This technology is available via the operating system: a container “packages” the application’s service or function with all of the libraries, configuration files, dependencies, and other items and settings needed for it to work.
Each container shares the services of a single underlying OS. Docker images contain all the dependencies required to run code inside a container, so that the container can switch from one Docker environment to another with the same OS and run with no changes.
Docker runs multiple containers on the same system through resource isolation in the OS kernel. This differs from a virtual machine (VM), which encapsulates an entire operating system with executable code on top of an abstract layer of physical hardware resources.
Docker was originally created to run on Linux, but its scope has been expanded to offer better support for non-Linux operating systems, such as Microsoft Windows and Apple OS X. Docker versions also exist for Amazon Web Services (AWS) and Microsoft Azure.
The advantages of Docker
Here are the main advantages of Docker:
Isolates lightweight applications:
Docker uses lightweight containers to ensure efficient isolation between apps and their dependencies. Each program runs autonomously and consistently, without interfering with others.
Application portability between different environments:
The containerised instances encapsulate the application and its dependencies. This makes it easy to deploy on different machines, whether they are local servers, VMs, or cloud containers, without having to worry about differences in environment.
Simplified creation, distribution, and deployment process:
Docker allows you to create containerised images of your apps and distribute them via Docker registries.
Improved developer productivity by standardising development environments:
Docker enables developers to work in consistent environments. This means that each team member has the same software dependencies and configurations, which reduces compatibility issues across versions.
Faster development cycles:
Docker containers are portable and can be deployed easily, allowing for faster program development, testing and deployment.
Simplified application scaling:
Docker makes it easy to scale apps, as new containers can be instantly deployed to meet growing demand. This provides a flexible and efficient solution for managing variable workloads.
Optimised resources and reduced infrastructure costs:
Hardware can be shared more efficiently, reducing infrastructure costs.
Enables collaboration:
Docker containers ensure full reproducibility of the development environment, making it easy for your developers to collaborate, while ensuring they can all work in a consistent, isolated environment.
Docker vs Virtual Machines
A virtual machine (VM) is a software emulation of a physical computer system that runs in a host computing environment. It is isolated from this system, which ensures that the VM software cannot affect the main system.
VMs are commonly used for tasks such as accessing virus-infected data, testing operating systems, and creating backups. These backups consist of various files, including log files, NVRAM settings, virtual disk files, and configuration files.
VMs are also used in server virtualisation, where a physical server is divided into several isolated servers, each running its OS independently.
There are two types of VMs: system VMs, which allow multiple VMs to share physical resources using a hypervisor, and process VMs. Together, they provide a programming environment that is independent of the platform.
Docker vs virtual machine: main differences
Here are the significant differences between Docker and VMs.
OS and architecture support
The main difference between Docker and VMs lies in their architecture. VMs include a host operating system and a guest OS inside each VM. A guest operating system can be any OS, such as Linux or Windows, regardless of the main OS.
Containerised instances are hosted on a single physical server with an operating system that they share with each other. Sharing the host OS between containers makes them lighter and increases boot time.
Docker containers are better suited to running multiple programs on a single operating system kernel, while VMs are required if services need to run on different operating systems.
Security level
The second difference between VMs and Docker is that virtual machines are self-contained with their kernel and security features. As a result, applications that require more privileges and security are run on virtual machines.
On the other hand, it is not recommended to provide root access to applications and run them with administrative premises in the case of containerised instances, as they share the host kernel. Docker technology has access to the kernel subsystems, therefore a single infected application is capable of hacking the entire host system.
Portability
Another important difference between Docker and VMs is portability: VMs are isolated from their OS and therefore cannot be ported across multiple platforms without causing compatibility issues.
At the development level, if an application needs to be tested on different platforms, then Docker containers should be considered, as they are standalone and can run applications in any environment.
As they do not require a guest OS, they can be easily ported to different platforms. Docker containers can be deployed to servers because containers are lightweight. This means that they can be started and stopped in less time than virtual machines.
Performance level
The final difference between Docker and VMs is performance: Docker containers are less resource-intensive, as VMs need to load the entire operating system in order to boot up.
In the case of a virtual machine, resources such as CPU, memory, and input/output may not be permanently allocated to containers, unlike a Docker container. The resources are then used according to traffic levels.
Scaling and replicating a Docker container is simple and easy compared to a virtual machine, as there is no need to install an operating system.
Uses for Docker
Although it is technically possible to use Docker to develop and distribute any type of software application, it is especially useful for accomplishing the following tasks:
App development
By combining Docker with DevOps best practices, containerised applications can be deployed in seconds, unlike traditional large monolithic applications that take much longer.
Updates or changes to an application's code are implemented and deployed quickly when containers are used as part of a larger continuous integration pipeline.
Application management via a standardised image format
Docker’s portable, standardised image format simplifies app management by encapsulating all necessary dependencies and configurations into a single image. This ensures consistency and reproducibility across different IT environments,
so that you can seamlessly develop, package and distribute applications on any Docker-compatible platform.
Developing a microservices-based architecture
Docker is ideal for creating a microservices-based architecture. This is more convenient than a traditional program. You can create and deploy several microservices, each in its own container, then integrate them to assemble a complete program using a container orchestration tool.
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Microservices are an architectural and organisational approach to software development where the software is composed of small, independent services that communicate over well-defined APIs. These services belong to small, autonomous teams.
Migrating existing programs to a containerised infrastructure
A development team that wants to modernise an existing program can use Docker to migrate the application to a containerised infrastructure.
Implementing hybrid and multi-cloud solutions
Docker containers all work in the same way, whether they are deployed on-premises or use cloud computing. Docker makes it easy to move applications to the production and test environments of various cloud providers.
A Docker program that uses multiple cloud solutions can be considered a hybrid cloud or multi-cloud. Businesses can also take advantage of cloud container services such as Kubernetes, which provide management and orchestration platforms for containers in cloud environments.
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With Kubernetes as a Service (KaaS), you can take a simple approach to deploying and managing Kubernetes clusters, without having to manage the underlying infrastructure. This allows development teams to focus on building and maintaining applications, rather than managing the infrastructure.
Containerisation using Docker makes it easy to build, distribute, and deploy applications by encapsulating applications and their dependencies in lightweight containers. The Docker images serve as templates for creating Docker containers, providing an efficient and repeatable way to manage applications and their runtime environments.
OVHcloud and Docker
Free Managed Kubernetes® service to orchestrate your containers
Kubernetes® is one of the most widely-used container orchestration tools on the market. It is used by companies of all sizes. It can be used to deploy applications, scale them up and make them more resilient – even in hybrid or multi-cloud infrastructures.
Service Managed Kubernetes® is powered by OVHcloud Public Cloud instances. With OVHcloud Load Balancers and additional disks integrated into it, you can host any kind of work load on it with total reversibility.
FAQ
What is Docker used for?
Docker is a lightweight virtualisation tool that allows you to create, manage and run containers. This efficient solution enables you to build and deploy applications across a variety of computing environments. Its utility lies in its ability to provide a consistent and isolated environment for applications, facilitating their design, distribution and execution.
What is a Docker container?
A Docker container is a lightweight, self-contained execution unit that encapsulates a program and its dependencies, enabling it to be deployed and run in various computing environments in a consistent manner. Docker containers use the virtualisation features of the host OS to isolate applications from one another, while efficiently sharing system resources.
Why install Docker?
Installing Docker brings you the benefits of lightweight virtualisation and container management. It enables software to be built, tested and deployed in a variety of computing environments, while ensuring application consistency and portability.
What are the advantages and disadvantages of using Docker?
The benefits of using Docker include application isolation, improved portability, simplified software creation and deployment, improved developer productivity, easier collaboration, and an optimised system. its potential downsides, however, relate to the complexity of its configuration, managing images and containers, and the potential for security issues linked to the use of shared containers.