What is a container in docker

In docker, a container is a runtime instance of an image, similar to a lightweight sandbox, which can be started, started, stopped, and deleted. Docker uses containers to run and isolate applications; each container is an isolated and secure platform.

The operating environment of this tutorial: linux5.9.8 system, docker-1.13.1 version, Dell G3 computer.

Docker includes three basic concepts

• Image

• Container

• Repository

##Docker image

Docker image (Image) is similar to the image of a virtual machine, which can be It is understood as a read-only template for the Docker engine, including the file system.

For example: an image can completely contain the Ubuntu operating system environment, and it can be called an Ubuntu image. The image can also have an Apache application (or other software) installed, which can be called an Apache image.

Images are the basis for creating Docker containers. Through version management and incremental file systems, Docker provides a very simple mechanism to create and update existing images. Users can download a prepared application image from the Internet and use it directly through commands. In short, an application requires an environment to run, and mirroring is here to provide this environment.

Docker container

Docker container (Container) is similar to a lightweight sandbox (because Docker is a virtual technology based on the Linux kernel, it consumes very few resources ), Docker uses containers to run and isolate applications.

A container is a runtime instance of an image. It can be started, started, stopped, deleted. Each container is an isolated and secure platform.

Schematic diagram of using a single Docker image to start multiple containers

You can think of a container as a simplified version of the Linux environment (including root user permissions, process space, user space and cyberspace, etc.) and the applications running therein.

The image itself is read-only. When a container is started from an image, Docker will create a writable layer on top of the image, and the image itself will remain unchanged. Just like after installing the system with ISO, the ISO has not changed much.

Docker warehouse

Docker warehouse (Repository) is similar to a code warehouse and is a place where Docker stores image files centrally.

Each warehouse can contain multiple tags, and each tag corresponds to an image. Usually, a warehouse will contain images of different versions of the same software, and tags are often used to correspond to each version of the software.

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