1.Docker初体验

Docker
容器化
发布日期:   2021-03-08
文章字数:   2.7k
阅读时长:   13 分
阅读次数:  

1 What is Docker

1.1 官网首页

https://www.docker.com/

Modernize your applications, accelerate innovation Securely build, share and run modern applications anywhere

1.2 Docs

https://docs.docker.com/get-started/

Docker is a platform for developers and sysadmins to develop, deploy, and run applications with containers. The use of Linux containers to deploy applications is called containerization. Containers are not new, but their use for easily deploying applications is.

1.3 不理解，我太难了

不妨从一个需求开始 ：开发好了一个项目shopping，部署上线

  • 远古时代

    问题 ：成本高、部署慢、浪费资源、硬件限制、不利于迁移扩展

  • 虚拟化时代

    优点 ：相对利用好资源，相对容易扩展等。
    缺点 ：虚拟机太重了，一上来占用较多物理资源，移植性差，资源利用率低等。

  • 容器时代

1.4 再次理解Docker

Docker is a platform for developers and sysadmins to develop, deploy, and run applications with containers. The use of Linux containers to deploy applications is called containerization. Containers are not new, but their use for easily deploying applications is.

发现还是比较容易理解的，但是这里有一句 “Containers are not new”，也就是容器化技术很早就出现了，比如常见的容器化技术有OpenVZ，LXC，RKT等

1.5 Docker的优势和应用场景

www.docker.com —>Solutions

(1)有助于Microservices的落地和部署
(2)充分利用物理机资源，同时能够整合服务器资源
(3)提高开发效率，测试效率，部署效率，有利于DevOps的落地，CICD
(4)云原生落地，应用更好地迁移
…

2 What is Image and Container?

2.1 What is Image?

Why is docker?->What is a container

A Docker container image is a lightweight, standalone, executable package of software that includes everything needed to run an application: code, runtime, system tools, system libraries and settings.

2.2 What is Container？

Why is docker?->What is a container

A container is a standard unit of software that packages up code and all its dependencies so the application runs quickly and reliably from one computing environment to another.

2.3 Relation between image and container

Container images become containers at runtime and in the case of Docker containers- images become containers when they run on Docker Engine.

2.4 View from Docs

从帮助文档的角度看
docker官网->Resources->Docs->Get started->Get started with Docker->Orientation->Images
and containers

A container is launched by running an image. An image is an executable package hat includes everything needed to run an application--the code, a runtime, libraries, environment variables, and configuration files.

A container is a runtime instance of an image--what the image becomes in memory when executed (that is, an image with state, or a user process). You can see a list of your running containers with the command, docker ps, just as you would in Linux.

3 Containers and virtual machines

docker官网](www.docker.com)->Resources->Docs->Get started->Get started with Docker-

Orientation->Containers and virtual machines

A container runs natively on Linux and shares the kernel of the host machine with other containers. It runs a discrete process, taking no more memory than any other executable, making it lightweight.

By contrast, a virtual machine (VM) runs a full-blown “guest” operating system with virtual access to host resources through a hypervisor. In general, VMs provide an environment with more resources than most applications need.

4 Docker Engine and Architecture

https://docs.docker.com/engine/docker-overview/

4.1 Docker Engine

Docker Engine is a client-server application with these major components:

  • A server which is a type of long-running program called a daemon process (the dockerd command).
  • A REST API which specifies interfaces that programs can use to talk to the daemon and instruct it what to do.
  • A command line interface (CLI) client (the docker command).

4.2 Docker Architecture

Docker uses a client-server architecture. The Docker client talks to the Docker daemon, which does the heavy lifting of building, running, and distributing your Docker containers. The Docker client and daemon can run on the same system, or you can connect a Docker client to a remote Docker daemon. The Docker client and daemon communicate using a REST API, over UNIX sockets or a network interface.

5 Install and Experience

https://docs.docker.com/install/linux/docker-ce/centos/

5.1 在Win10上准备centos7

和大家说明一下，我们的目的仅仅是要安装一个centos7，然后在centos7上安装docker

如果搞不定vagrant+virtualbox的方式，也可以直接使用VM搭建一个centos7

或者你可以直接使用一台云服务器，上面安装了centos7

毕竟我们的目的只是为了得到一个centos7的机器，所以不必花太多精力在这个问题上折腾

演示环境是
【
    win10 64位
    VirtualBox-6.0.12-133076-Win
    vagrant_2.2.6_x86_64
    centos7
    XShell6
】

采用vagrant+virtual box

5.1.1 下载安装vagrant

01 访问Vagrant官网
https://www.vagrantup.com/

02 点击Download
Windows，MacOS，Linux等

03 选择对应的版本

04 傻瓜式安装

05 命令行输入vagrant，测试是否安装成功

5.1.2 下载安装virtual box

01 访问VirtualBox官网
    https://www.virtualbox.org/

02 选择左侧的“Downloads”

03 选择对应的操作系统版本

04 傻瓜式安装

05 [win10中若出现]安装virtualbox快完成时立即回滚，并提示安装出现严重错误
    (1)打开服务
    (2)找到Device Install Service和Device Setup Manager，然后启动
    (3)再次尝试安装

5.1.3 安装centos7

01 创建centos7文件夹，并进入其中[目录全路径不要有中文字符]

02 在此目录下打开cmd，运行vagrant init centos/7
   此时会在当前目录下生成Vagrantfile，同时指定使用的镜像为centos/7，关键是这个镜像在哪里，我已经提前准备好了，名称是virtualbox.box文件

03 将virtualbox.box文件添加到vagrant管理的镜像中
    (1)下载网盘中的virtualbox.box文件
    (2)保存到磁盘的某个目录，比如D:\virtualbox.box
    (3)添加镜像并起名叫centos/7：vagrant box add centos/7 D:\virtualbox.box
    (4)vagrant box list  查看本地的box[这时候可以看到centos/7]

04 centos/7镜像有了，根据Vagrantfile文件启动创建虚拟机
    来到centos7文件夹，在此目录打开cmd窗口，执行vagrant up[打开virtual box观察，可以发现centos7创建成功]

05 以后大家操作虚拟机，还是要在centos文件夹打开cmd窗口操作
    vagrant halt   优雅关闭
    vagrant up     正常启动

06 vagrant常用命令
    (1)vagrant ssh    
        进入刚才创建的centos7中
    (2)vagrant status
        查看centos7的状态
    (3)vagrant halt
        停止/关闭centos7
    (4)vagrant destroy
        删除centos7
    (5)vagrant status
        查看当前vagrant创建的虚拟机
    (6)Vagrantfile中也可以写脚本命令，使得centos7更加丰富
        但是要注意，修改了Vagrantfile，要想使正常运行的centos7生效，必须使用vagrant reload

至此，使用vagrant+virtualbox搭建centos7完成，后面可以修改Vagrantfile对虚拟机进行相应配置

5.1.4 通过Xshell连接centos7

01 使用centos7的默认账号连接
    在centos文件夹下执行vagrant ssh-config
    关注:Hostname  Port  IdentityFile
    IP:127.0.0.1
    port:2222
    用户名:vagrant
    密码:vagrant
    文件:Identityfile指向的文件private-key

02 使用root账户登录
    vagrant ssh   进入到虚拟机中
    sudo -i
    vi /etc/ssh/sshd_config
    修改PasswordAuthentication yes
    passwd修改密码，比如abc123
    systemctl restart sshd
    使用账号root，密码abc123进行登录

5.1.5 Vagrantfile通用写法

# -*- mode: ruby -*-
# vi: set ft=ruby :

# All Vagrant configuration is done below. The "2" in Vagrant.configure
# configures the configuration version (we support older styles for
# backwards compatibility). Please don't change it unless you know what
# you're doing.
Vagrant.configure("2") do |config|
  # The most common configuration options are documented and commented below.
  # For a complete reference, please see the online documentation at
  # https://docs.vagrantup.com.

  # Every Vagrant development environment requires a box. You can search for
  # boxes at https://vagrantcloud.com/search.
  config.vm.box = "centos/7"

  # Disable automatic box update checking. If you disable this, then
  # boxes will only be checked for updates when the user runs
  # `vagrant box outdated`. This is not recommended.
  # config.vm.box_check_update = false

  # Create a forwarded port mapping which allows access to a specific port
  # within the machine from a port on the host machine. In the example below,
  # accessing "localhost:8080" will access port 80 on the guest machine.
  # NOTE: This will enable public access to the opened port
  # config.vm.network "forwarded_port", guest: 80, host: 8080

  # Create a forwarded port mapping which allows access to a specific port
  # within the machine from a port on the host machine and only allow access
  # via 127.0.0.1 to disable public access
  # config.vm.network "forwarded_port", guest: 80, host: 8080, host_ip: "127.0.0.1"

  # Create a private network, which allows host-only access to the machine
  # using a specific IP.
  # config.vm.network "private_network", ip: "192.168.33.10"

  # Create a public network, which generally matched to bridged network.
  # Bridged networks make the machine appear as another physical device on
  # your network.
  config.vm.network "public_network"

  # Share an additional folder to the guest VM. The first argument is
  # the path on the host to the actual folder. The second argument is
  # the path on the guest to mount the folder. And the optional third
  # argument is a set of non-required options.
  # config.vm.synced_folder "../data", "/vagrant_data"

  # Provider-specific configuration so you can fine-tune various
  # backing providers for Vagrant. These expose provider-specific options.
  # Example for VirtualBox:
  #
  # config.vm.provider "virtualbox" do |vb|
  #   # Display the VirtualBox GUI when booting the machine
  #   vb.gui = true
  #
  #   # Customize the amount of memory on the VM:
  #   vb.memory = "1024"
  # end
    config.vm.provider "virtualbox" do |vb|
        vb.memory = "4000"
        vb.name= "jack-centos7"
        vb.cpus= 2
    end
  #
  # View the documentation for the provider you are using for more
  # information on available options.

  # Enable provisioning with a shell script. Additional provisioners such as
  # Puppet, Chef, Ansible, Salt, and Docker are also available. Please see the
  # documentation for more information about their specific syntax and use.
  # config.vm.provision "shell", inline: <<-SHELL
  #   apt-get update
  #   apt-get install -y apache2
  # SHELL
end

5.1.6 box的打包分发

01 退出虚拟机
    vagrant halt

02 打包
    vagrant package --output first-docker-centos7.box

03 得到first-docker-centos7.box

04 将first-docker-centos7.box添加到其他的vagrant环境中
    vagrant box add first-docker-centos7 first-docker-centos7.box

05 得到Vagrantfile
    vagrant init first-docker-centos7

06 根据Vagrantfile启动虚拟机
    vagrant up [此时可以得到和之前一模一样的环境，但是网络要重新配置]

5.2 安装docker

https://docs.docker.com/install/linux/docker-ce/centos/

  1. 进入centos7

    vagrant ssh

  2. 卸载之前的docker

    sudo yum remove docker \
               docker-client \
               docker-client-latest \
               docker-common \
               docker-latest \
               docker-latest-logrotate \
               docker-logrotate \
               docker-engine
    docker 卸载不干净
例如：
官网介绍docker卸载的方法一般为
1> yum remove docker-ce -y
2> rm -fr /var/lib/docker*
但试过后你依然无法安装新版本，尤其是高版本降到低版本docker，问题在于docker你并没有卸载干净
正确的卸载方法如下：
1> yum list installed|grep docker 查看
2> yum remove [docker名称]

  3. 安装必要的依赖

    sudo yum install -y yum-utils \
device-mapper-persistent-data \
lvm2

  4. 设置docker仓库 [设置阿里云镜像仓库可以先自行百度，后面课程也会有自己的docker hub讲解] 

    sudo yum-config-manager \
   --add-repo \
   https://download.docker.com/linux/centos/docker-ce.repo

    [访问这个地址，使用自己的阿里云账号登录，查看菜单栏左下角，发现有一个镜像加速器]

  5. 安装docker

    sudo yum install -y docker-ce docker-ce-cli containerd.io

  6. 启动docker

    sudo systemctl start docker

  7. 测试docker安装是否成功

    sudo docker run hello-world

5.3 docker基本体验

01 创建tomcat容器
    docker pull tomcat
    docker run -d --name my-tomcat -p 9090:8080 tomcat

02 创建mysql容器
    docker run -d --name my-mysql -p 3301:3306 -e MYSQL_ROOT_PASSWORD=jack123 --privileged mysql

03 进入到容器里面
    docker exec -it containerid /bin/bash

5.4 可能有的疑惑

(1)docker pull在哪拉取的镜像？

默认是在hub.docker.com

(2)docker pull tomcat拉取的版本是？

默认是最新的版本，可以在后面指定版本":"

(3)简单先说一下命令咯

docker pull        拉取镜像到本地
docker run         根据某个镜像创建容器
-d                 让容器在后台运行，其实就是一个进程
--name             给容器指定一个名字
-p                 将容器的端口映射到宿主机的端口
docker exec -it    进入到某个容器中并交互式运行
文章作者: Soulballad
文章链接: https://soulballad.github.io/posts/41ccce2c
版权声明: 本博客所有文章除特別声明外，均采用 CC BY 4.0 许可协议。转载请注明来源 Soulballad !
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