Docker Hello-World镜像运行测试

一、命令：docker run hello-world

命令解释：以docker客户端命令的方式运行hello-world镜像

命令运行结果：

 hadoop@Docker:/opt/docker$ docker run hello-world
    Unable to find image 'hello-world:latest' locally
    latest: Pulling from library/hello-world
    d1725b59e92d: Pull complete
    Digest: sha256:0add3ace90ecb4adbf7777e9aacf18357296e799f81cabc9fde470971e499788
    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:

通过分析命令运行结果，说明docker内部的工作原理：

（1）加载本地镜像

    # 首先在本地查找'hello-world:latest'镜像
    Unable to find image 'hello-world:latest' locally

docker run一个镜像，那么则会以这个镜像作为类的模板生成一个hello-world容器实例，一个具体的对象。注意：该命令首先会查找本地的hello-world镜像。
（2）从阿里云服务器上拉去hello-world镜像

latest: Pulling from library/hello-world
d1725b59e92d: Pull complete
Digest: sha256:0add3ace90ecb4adbf7777e9aacf18357296e799f81cabc9fde470971e499788
Status: Downloaded newer image for hello-world:latest

（3）、运行

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

（4）运行原理分析

首先，我们在docker客户端（命令行终端窗口）,执行docker命令；
客户端回去访问我们docker所在的那台服务器主机，实质而言主机上有一个Docker daemon主线程，它会监听到客户端的docker命令，它会run容器（Container）,而容器又是通过镜像生成的。如果没有hello-world容器，它就会在本地查找hello-world镜像，如果本地找到了就会直接生成一个hello-world容器，否则，会向阿里云服务器仓库拉去相应的镜像；
从阿里云服务器仓库上拉取hello-world镜像到本地，再生成容器，进而运行。
（5）docker容器终止运行

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/

输出这段提示以后，hello world就会停止运行，容器自动终止

二、run到底做了什么呢？

docker run hello-world命令运行原理图：