What is docker cluster and mirror

A cluster is a group of machines running Docker, each machine is called a node; the image is a special file system, in addition to providing the programs, libraries, resources, configuration, etc. required for the container to run In addition to the file, it also contains some configuration parameters prepared for runtime.

The operating environment of this tutorial: linux7.3 system, docker-1.13.1 version, Dell G3 computer.

What is docker cluster and mirroring

1. A cluster is a group of multiple machines running docker and added to a group.

After joining the cluster, you can continue to run your own docker commands, but now these machines are executed on the cluster by the cluster manager. The machines in the cluster can be physical or virtual. After joining the group, each machine is called a node.

The cluster manager can use different strategies to manage running containers, for example: the emptiest node command is used to fill the least utilized containers; global ensures that each machine can only get one instance of the specified container. You can write these policies to a file to enforce the cluster manager's policies.

The cluster manager is the only machine in the cluster that can execute commands. You can also authorize other machines to join the cluster management work.

2. The image is the cornerstone of the Docker container. The container is the running instance of the image. Only with the image can the container be started.

Docker image can be regarded as a special file system. In addition to providing the programs, libraries, resources, configuration and other files required for container runtime, it also contains some configuration parameters prepared for runtime ( Such as anonymous volumes, environment variables, users, etc.). The image does not contain any dynamic data, and its content will not be changed after it is built.

The image provides a basic operating system environment, and users can install and configure software as needed. Each image will have a text file Dockerfile that defines how to build the Docker image. The new image is generated from the base image layer by layer. Each time you install a software, it is equivalent to adding a layer to the existing image. The benefit of using a layered structure for Docker images is shared resources.

When the container starts, a new writable layer is loaded on top of the image. This layer is called the container layer, and everything below the container layer is called the image layer. Only the container layer is writable, and all image layers below the container layer are read-only. Any changes to the container will only happen at the container layer.

Here, all the mirror layers are combined to form a unified file system. What the user sees at the container layer is a superimposed file system.

Recommended learning: "docker video tutorial"

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