What are the internal components of docker?

Docker internal components include: 1. dockerclient, which is a general term. It can be a command line docker or a client that follows the docker api rules; 2. dockerserver server; 3. Docker image, This is a read-only template and is the basis for starting a container; 4. Registry, which is a mirror warehouse; 5. Docker container.

The operating environment of this tutorial: linux7.3 system, docker version 19.03, Dell G3 computer.

What are the internal components of docker?

The core components of docker are as follows:

1. Client: dockerclient

2. Server: dockerserver

3. Docker image

4. Registry

5. Docker container

This article will briefly introduce the functions of these components and briefly describe how they cooperate with each other

1 , docker client and server

Docker client sends a request to docker daemon, docker daemon completes the corresponding task and returns the result to the container

docker client is a general term, it can be a command line Docker can also be a client that follows the rules of docker api. Simply put, it can be understood as an interface for interacting/sending instructions.

As shown below:

2. Docker image

The docker image is a read-only template and is the basis for starting a container. This includes the file system structure and content of the container, which together with the docker configuration file constitute the static file system environment of the docker container.

The docker image has many special features in its design:

Layered mechanism

Docker's mirroring mechanism is hierarchical, and one mirror can be placed on top of another mirror. The one at the bottom is the parent image, and so on; the image at the bottom can be called the base image. When finally starting a container from an image, docker will load a read-write file system on the top layer of the image. The program we want to run on docker is executed in this read-write layer.

I’m afraid you didn’t understand, the picture above

#When I start the container, we are exposed to the top-level writable container and the top-level image It is built iteratively from the image at its distribution layer. Next, another feature of the docker image is introduced, copy-on-write:

2) Copy-on-write

Look at the picture just now. The container and top-level image can be written when it first starts running. The content is completely consistent; when I modify the content, the file will be copied from the next layer of mirror (read-only layer) to the top-level writable container (read-write layer). The files in the read-only layer still exist, but It will be hidden by the files in the read-write layer; all operations done in the container will not affect the original underlying data unless you package it into a new image.

3) Content addressing and joint mounting

. . . Let me be lazy and use Baidu if you are interested

3. Registry

Where can we get the image? If we start a container through a certain image for the first time, first the host will go back to the /var/lib/docker directory to find it. If it is not found, it will go to the registry to download the image and store it in the virtual machine, and then complete the startup.

Registry can be imagined as a mirror warehouse. The default registry is the registry service officially provided by docker, called Docker Hub. Of course, you can also build your own mirror warehouse.

4. Docker container

The container is the running instance of the image.

Users can start, stop, move or delete containers through the command line or API. It can be said that for application software, the image is the construction and packaging phase of the software life cycle, while the container is the startup and running phase.

Recommended learning: "docker video tutorial"

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