Docker is a revolutionary containerization platform that has transformed how we develop, ship, and run applications. It allows developers to package applications along with all their dependencies into lightweight, portable containers. These containers ensure that applications run consistently across different environments, from development laptops to production servers.
Docker follows a client-server architecture with several key components. The Docker Client is the command-line interface that users interact with to run Docker commands. The Docker Daemon is a background service that manages Docker objects like containers, images, and networks. The Docker Registry stores and distributes Docker images, with Docker Hub being the most popular public registry. These components communicate through a REST API, enabling seamless interaction between different parts of the Docker ecosystem.
The Docker workflow is straightforward and follows a logical sequence. First, developers write a Dockerfile containing instructions for building an application environment. Next, they use the docker build command to create a Docker image from the Dockerfile. This image serves as a template. Then, containers are created and run from this image using docker run. Finally, images can be shared by pushing them to a registry like Docker Hub, where others can pull and use them. This workflow ensures consistency and portability across different environments.
Docker achieves container isolation through several Linux kernel technologies. Namespaces provide process isolation, ensuring each container has its own view of system resources like process IDs, network interfaces, and filesystems. Control Groups, or cgroups, limit and monitor resource usage such as CPU, memory, and disk I/O for each container. Union File Systems create layered filesystems that allow containers to share common base layers while maintaining their own writable layers. These technologies work together to ensure containers are isolated from each other and the host system, providing security and resource management.