Docker is a popular software platform for simplifying the process of development, testing, and deploying applications. In this article, we will take a closer look at Docker, its functionality, and how and where it can be useful.
What is Docker
Docker is an open-source product used to automatically deploy applications. They are organized into self-contained, portable containers and run in a cloud or on-premises environment.
With the Docker platform, testing and deploying applications becomes much faster. Developers no longer need to think about the environment in which the application will run, and whether it has the required features and dependencies for testing. All dependencies and processes are packaged in a container together with the application, so they can run on any system: Linux, Windows, and macOS. In this way, applications are no longer dependent on infrastructure and can be moved easily and smoothly.
The containerization technique is similar to virtualization in some ways, but with significant differences. Virtualization allows creating a separate virtual computer inside the server with the right amount of resources, installed OS, and software. Containerization, on the other hand, runs the virtual environment from the operating system kernel, without implementing the virtualization of physical resources.
Containers features and capabilities
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Relatively short lifecycle. Any container can be suspended, restarted, or deleted if necessary. When a container is deleted, all data is also completely destroyed, so it is not recommended to keep important information in the container.
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Small size. Container size is usually measured in megabytes. If they are not large, you run them faster and save disk space.
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One container equals a single process. This ensures that if one container is disabled, the rest of the application will not stop running.
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Increased security. Containerization allows isolating processes – applications in a container do not access the main operating system.
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Containers enable automatic deployment of applications to different hosts.
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Minimal resources required. On the same hardware, you can run more containers than virtual machines.
Docker architecture and components
Dockerfile. A document with instructions on creating a Docker image. Each line corresponds to one command.
Daemon. The background service on the host is responsible for preparing, launching, and removing containers.
Docker Image is a file that contains the source code, libraries, dependencies, tools, and other files to run the application.
Client. The Client is used to control Daemon as well as handle any interaction with the container.
Container. The application deployed from the image.
Registry. Docker service serves as a repository. You can use it to monitor image versions, and make private repositories.
Docker Hub. A well-known public repository that is used by default. Enables integration with GitHub.
Docker Desktop. Application for local work with containers.
Docker volumes. Volumes that serve for persistent data storage. They help to better configure data storage.
Docker image architecture
The base image of the Docker containerization contains the processes and dependencies that enable running applications. A read-only layer is applied to the base image on top of the image. They appear after any elements are added to the image. Each layer is saved, so you can undo everything if necessary.
A container differs from an image by having one more layer on top. You can always create a new container from an old image.
Each image stores a Docker manifest. This is a JSON file that contains data about the image: links to layers, their sizes, hash, and platform data.
Conclusion
The use of images and containers gives you the opportunity to make complex application architecture easier and automate many processes. If you want to work with containers, Cloud4Y offers a user-friendly Kubernetes platform. It is suitable for automating containers on Ubuntu, CentOS, and other Linux operating systems. You will be able to centrally group containers, perform load balancing, etc.
