Docker learning one, what is Docker

Docker learning one

What is Docker

Website: https://hub.docker.com/

docker encapsulates and isolates processes, which is a virtualization technology at the operating system level

Since the isolated process is independent of the host and other isolated processes, it is also called a container

docker application scenario

Automated testing and continuous integration, release
Automated packaging and publishing of web applications
Easy deployment of background applications

Advantages of

Fast and consistent delivery of applications
Portable and extensible
Lightweight, fast, economical and efficient, squeezing linux own resources

What can Docker do?

Let me first talk about the difference between Docker and virtual machines

In the previous virtual machine, the system occupies a lot of resources, many steps are redundant, and the startup is still very slow, which is unbearable

Docker now looks like this,

The containers are isolated from each other and interfere with each other, and run together on the same operating system to maximize the use of operating system resources

the difference between Docker technology and virtual machine technology?

Each container is isolated from each other, they have their own file system and will not affect each other
The container does not have its own kernel or its own hardware. The application in the container runs directly in the kernel of the host machine.
The traditional virtual machine is to virtualize a piece of hardware, run the completed operating system, and run applications on it

So what can Docker specifically do?

Do DevOps

There are several improvements in DevOps:

Applications can be deployed and delivered faster

The troublesome installation steps in the past are gone forever, after using Docker containerization, package the image to release the test, one-click deployment and operation

Can be upgraded and expanded more conveniently

Use Docker to package the project into a mirror, easy to upgrade and easy to expand

Development, operation and maintenance, and testing will be easier

No longer have to worry about the inconsistency of the development environment, test environment, and operation and maintenance environment

Use resources more efficiently

Dcoker runs in the kernel of the host, and multiple Docker instances can be deployed on this physical host

The composition of Docker

Docker uses a client-server (C/S) architecture model, using remote APIs to manage and create Docker containers

Three basic concepts of Docker:

The picture comes from the Internet

Mirroring

It is equivalent to a root file system, similar to a template, which is static

container

It is equivalent to an instance pulled from the template. The container is created by mirroring. We can create, start, stop, pause, delete, etc.

storehouse

Used to save the image, it can be regarded as a code control center

Docker installation and use

Install

There are roughly the following ways to install Docker on the network:

Automatic installation of official script
Install using Docker repository
Use ==shell== script installation

Let's take the ubuntu system as an example, and use the Docker warehouse to install. My ubuntu system version is as follows:

# cat /etc/os-release
NAME="Ubuntu"
VERSION="18.04.5 LTS (Bionic Beaver)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 18.04.5 LTS"
VERSION_ID="18.04"
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
VERSION_CODENAME=bionic
UBUNTU_CODENAME=bionic

Set up warehouse

Install dependencies

sudo apt-get update
sudo apt-get install \
    apt-transport-https \
    ca-certificates \
    curl \
    gnupg-agent \
    software-properties-common

Add Docker's official GPG key:

curl -fsSL https://mirrors.ustc.edu.cn/docker-ce/linux/ubuntu/gpg | sudo apt-key add -

To verify the secret key, you can directly search for the 8 characters after 9DC8 5822 9FC7 DD38 854A E2D8 8D81 803C 0EBF CD88

sudo apt-key fingerprint 0EBFCD88

The following output shows that the secret key is set correctly

pub   rsa4096 2017-02-22 [SCEA]
      9DC8 5822 9FC7 DD38 854A  E2D8 8D81 803C 0EBF CD88
uid           [ unknown] Docker Release (CE deb) <docker@docker.com>
sub   rsa4096 2017-02-22 [S]

Set up a stable version of the warehouse

sudo add-apt-repository \
   "deb [arch=amd64] https://mirrors.ustc.edu.cn/docker-ce/linux/ubuntu/ \
  $(lsb_release -cs) \
  stable"

Install Docker

Install the latest Docker version

sudo apt-get update
sudo apt-get install docker-ce docker-ce-cli containerd.io

After the installation is complete, verify that it is OK

You can check the version of docker docker version

# docker version
Client: Docker Engine - Community
 Version:           20.10.7
 API version:       1.41
 Go version:        go1.13.15
 Git commit:        f0df350
 Built:             Wed Jun  2 11:56:40 2021
 OS/Arch:           linux/amd64
 Context:           default
 Experimental:      true

Server: Docker Engine - Community
 Engine:
  Version:          20.10.7
  API version:      1.41 (minimum version 1.12)
  Go version:       go1.13.15
  Git commit:       b0f5bc3
  Built:            Wed Jun  2 11:54:48 2021
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.4.8
  GitCommit:        7eba5930496d9bbe375fdf71603e610ad737d2b2
 runc:
  Version:          1.0.0
  GitCommit:        v1.0.0-0-g84113ee
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

Run a hello-world

sudo docker run hello-world

The following message appears, indicating that the docker installation is successful

Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
b8dfde127a29: Pull complete
Digest: sha256:df5f5184104426b65967e016ff2ac0bfcd44ad7899ca3bbcf8e44e4461491a9e
Status: Downloaded newer image for hello-world:latest

Hello from Docker!
This message shows that your installation appears to be working correctly.

To generate this message, Docker took the following steps:
 1. The Docker client contacted the Docker daemon.
 2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
    (amd64)
 3. The Docker daemon created a new container from that image which runs the
    executable that produces the output you are currently reading.
 4. The Docker daemon streamed that output to the Docker client, which sent it
    to your terminal.

To try something more ambitious, you can run an Ubuntu container with:
 $ docker run -it ubuntu bash

Share images, automate workflows, and more with a free Docker ID:
 https://hub.docker.com/

For more examples and ideas, visit:
 https://docs.docker.com/get-started/

Of course, you can also choose not to install the latest version, or you can install the version you specify

Use ==apt-cache madison docker-ce== to view the versions available in the warehouse
Use ==sudo apt-get install docker-ce=<VERSION_STRING> docker-ce-cli=<VERSION_STRING> containerd.io== install the specified version of Docker
Use ==sudo docker run hello-world== to verify that the installation is successful

View docker image

# docker images
REPOSITORY        TAG       IMAGE ID       CREATED        SIZE
hello-world       latest    d1165f221234   4 months ago   13.3kB

docker image

卸载镜像
sudo apt-get purge docker-ce docker-ce-cli containerd.io

删除安装目录
/var/lib/docker 是docker 的默认安装路径
 sudo rm -rf /var/lib/docker
 sudo rm -rf /var/lib/containerd

Mirror acceleration

If you are a small partner using Alibaba Cloud server, you can see this step

To configure image acceleration, the installation version of docker needs to be above 1.10.0, and the version of docker we currently install is 1.41, which is fully in line with

We can use the accelerator by modifying the daemon configuration file /etc/docker/daemon.json , execute the following instructions

sudo mkdir -p /etc/docker
sudo tee /etc/docker/daemon.json <<-'EOF'
{
  "registry-mirrors": ["https://uhr5ub75.mirror.aliyuncs.com"]
}
EOF
sudo systemctl daemon-reload
sudo systemctl restart docker

The process of docker run

docker run Now find the corresponding mirror locally, and run it directly if there is one
If not, go to the docker hub to download, if there is, download to the local and run
If not, report an error directly

The underlying principle of Docker

How does Docker work?

Docker is a C/S model. The background guard of docker runs on the host, and the client and server communicate through sockets.

When the docker server receives an instruction from the docker client, it executes the instruction

Why is Docker faster than virtual machines?

I found a picture on the Internet, let’s compare it and it’s clear

As shown in the figure, the reasons why Docker is faster than virtual machines are as follows:

Docker has fewer abstraction layers than virtual machines
Docker uses the kernel of the host machine, and the virtual machine needs to create a new OS

Based on the above 2 points, when the virtual machine starts, it will load the operating system, the startup is slow, and the time is basically minutes.

When docker starts, there is no need to load the operating system kernel, so it is fast, and the time is basically seconds

Reference materials:

docker docs

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Docker learning one, what is Docker