Docker (1-1) docker introduction and installation

Docker introduction and installation

# 1. About Docker

# Basic concepts

Docker is an open source application container engine, which allows developers to package their applications and dependency packages into a portable container, and then publish them to any popular Linux machine, or realize virtualization.

Containers are completely sandboxed, and there will be no interface between them (similar to iPhone app s). With little performance overhead, it can easily run in machines and data centers. Most importantly, they do not rely on any language, framework or system.

# Implementation mode

The goal of docker project is to achieve a lightweight operating system virtualization solution. Docker is based on Linux container (LXC), Cgroup and other technologies.

On the basis of LXC, Docker is further encapsulated, so that users do not need to care about container management, making the operation easier. The user's operation of Docker container is as simple as that of a fast and lightweight virtual machine.

# The difference between Docker and traditional virtualization

The container realizes virtualization at the operating system level and directly reuses the operating system of the local host, while the traditional way is to virtualize its own system on the basis of hardware, and then deploy relevant APP applications on the system.

  • Traditional virtualization solutions:

  • Docker virtualization scheme:

Docker virtualization has three concepts to understand: image, container and warehouse.

  • Image: the image of docker is actually a template, similar to our common ISO image. It is a template.

  • Container: an application or system created using an image, which we call a container.

  • Warehouse: a warehouse is a place where images are stored. It is divided into two forms: Public warehouse and Private warehouse.

# Docker virtualization features

  • Fast operation start

    The performance of runtime can be greatly improved. Management operations (start, stop, start, restart, etc.) are in seconds or milliseconds.

  • Lightweight virtualization

    You will have enough "operating systems" to add or reduce images. Hundreds of Containers can be deployed on one server. But with traditional virtualization, it's good for you to virtualize 20 virtual machines.

  • Open source free

    Open source, free, low cost. Supported and driven by the modern Linux kernel. Lightweight containers can certainly open more "containers" on a physical machine, which is destined to be cheaper than VMs.

# 2. Preliminary preparations for installing Docker

  • Step 0: in the development environment, we usually turn off the firewall

    systemctl status firewalld  # View firewall status
    systemctl stop firewalld    # Close, effective only for the current
    systemctl disable firewalld # Boot disable
    
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  • Step 1: View kernel version

    Docker officially requires the Linux kernel version to be at least 3.8 or above, and it is recommended to be above 3.10. The kernel version can be viewed with the following command:

    uname -r
    
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    The kernel version of CentOS 7 meets its requirements.

  • Step 2: uninstall the old version

    The older docker version is called   docker   or   docker-engine  . If you have installed these programs, uninstall them and their related dependencies.

    yum remove docker \
          docker-client \
          docker-client-latest \
          docker-common \
          docker-latest \
          docker-latest-logrotate \
          docker-logrotate \
          docker-engine
    
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  • Step 3: prepare for configuring docker software source

    yum install -y \
          yum-utils \
          device-mapper-persistent-data \
          lvm2
    
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  • Step 4: add docker software source

    yum-config-manager \
          --add-repo  \
          https://download.docker.com/linux/centos/docker-ce.repo
    
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    Considering that downloading docker CE from docker's official warehouse is sometimes slow, you can use the following command to change the download website to Huawei's image server:

    sudo sed -i \
        's+download.docker.com+repo.huaweicloud.com/docker-ce+' \
        /etc/yum.repos.d/docker-ce.repo
    
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What have we done so far?

There is actually a docker installation package in the default Yum software source of CentOS. If you do it directly   yum install docker   It is also feasible.

However, considering that different users have different needs for different versions of docker (some pursue the latest and others pursue stability), docker officials have specially provided a warehouse / website to provide the download of multiple versions of docker.

Therefore, we must inform yum of the existence of such a warehouse, and ask yum to download the version of docker specified by us from this warehouse in the future. Instead of the default warehouse.

  • Step 5: validation

    View all docker versions in all warehouses

    yum list docker-ce --showduplicates | sort -r
    
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# 3. Install docker and verify

  • Download from the network warehouse and install the latest version

    yum install -y docker-ce
    
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    Or specify a specific version. For example:

    yum install -y docker-ce-18.06.3.ce-3.el7
    
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    The following questions will appear during installation:

    from https://download.docker.com/linux/centos/gpg retrieve key
     Import GPG key 0x621E9F35:
     user ID     : "Docker Release (CE rpm) <docker@docker.com>"
     fingerprint       : 060a 61c5 1b55 8a7f 742b 77aa c52f eb6b 621e 9f35
     come from       : https://download.docker.com/linux/centos/gpg
     Continue?[y/N]: 
    
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    input   y   Press enter to continue installation.

    Eventually:

    complete!
    
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  • Start Docker and add it to startup

    # systemctl start docker
    
    systemctl enable docker --now
    
    systemctl status docker
    
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    Similar results will appear as follows:

    Created symlink from /etc/systemd/system/multi-user.target.wants/docker.service to /usr/lib/systemd/system/docker.service.
    
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  • Verify that the installation was successful

    (there are two parts: client and service, which means that the installation and startup of docker are successful)

    input   docker version   Command, the following will appear:

    Client:
      Version:    17.12.1-ce
      API version:    1.35
      Go version:    go1.9.4
      Git commit:    7390fc6
      Built:    Tue Feb 27 22:15:20 2018
      OS/Arch:    linux/amd64
    
    Server:
     Engine:
       Version:    17.12.1-ce
       API version:    1.35 (minimum version 1.12)
       Go version:    go1.9.4
       Git commit:    7390fc6
       Built:    Tue Feb 27 22:17:54 2018
       OS/Arch:    linux/amd64
       Experimental:    false
    
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  • Verify the connection to the docker hub central image warehouse

    input   docker search -f is-official=true mysql   Command, the following results will appear:

    NAME     DESCRIPTION                                     STARS  OFFICIAL ...
    mysql    MySQL is a widely used, open-source relation...   8819   [OK]     ...
    mariadb  MariaDB is a community-developed fork of MyS...   3102   [OK]     ...
    percona  Percona Server is a fork of the MySQL relati...   459    [OK]     ...
    
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# 4. Configure domestic image

Since the central image warehouse of docker hub is located abroad, sometimes it is very moving for us to connect to docker hub and download images from it. Therefore, we need to configure the domestic image website to mirror files from home.

TIP

The domestic image is essentially a cache / backup of the docker hub central warehouse in China.

Edit the relevant configuration file through the vi command:

vi /etc/docker/daemon.json 
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If the file exists, its contents will be cleared; If the file does not exist, (after opening the file, its content is blank), save and exit after editing, that is, create.

Enter the following:

{
  "registry-mirrors": [
    "https://registry.docker-cn.com",
    "https://docker.mirrors.ustc.edu.cn"
  ]
}
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The configuration file is configured with two images, one is the official image of docker in China, and the other is an image maintained by China University of science and technology.

Restart docker service:

systemctl restart docker
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View modification results:

docker info
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There will be the following:

...
Registry Mirrors:
 https://registry.docker-cn.com/
 https://docker.mirrors.ustc.edu.cn/
...
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# 5. Import the existing image file

Considering the inconvenience of networking in some scenarios, docker provides the function of packaging and exporting downloaded images and importing them elsewhere.

To export an existing image, use the following command:

docker save <repository>:<tag> -o <repository>.tar
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For example:

docker save mysql:8.0.16 -o mysql-8.0.16.tar
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To import an image, use the following command:

docker load -i <repository>.tar
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For example:

docker load -i mysql-8.0.16.tar
 

Posted on Sat, 04 Dec 2021 20:22:41 -0500 by MesaFloyd