怎么理解Docker

Docker is a tool that can be used to create, deploy, and run applications by using containers. Containers allow a developer to package up an application with all of the parts it needs, such as libraries and other dependencies, and ship it all out as one package. By doing this, developers can rest assured that their application will run on any other Linux machine regardless of any customized settings that machine might have that could differ from the machine used to originally write and test the code. Docker is popular because it solves a number of problems that have plagued developers for a long time. First, it ensures that an application will always run the same, regardless of the environment it is deployed in. Second, it makes it easy to package and ship applications, and third, it provides a way to run multiple applications on the same host without them interfering with each other. Docker containers are built on top of a Linux kernel feature called namespaces. Namespaces provide a layer of isolation for processes running in a container. They prevent one container from seeing or interacting with the processes in another container. Docker also uses something called UnionFS to provide a way to combine multiple filesystems into a single view. This is how Docker can provide a consistent view of files to a container, even though the files may be stored in different places on the host machine. Docker containers are portable and can be run on any machine that has a Docker daemon running. The Docker daemon is a background process that manages the running of containers. Docker provides a command line interface (CLI) that can be used to interact with the Docker daemon. The CLI can be used to create, run, and stop containers. Docker also provides an API that can be used by developers to create their own tools that work with Docker.