Docker——初级学习

Docker——初级学习

标签：docker

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学习内容

1. 学习镜像、容器和虚拟机的区别
2. 学习使用Dockerfile来定义一个容器
3. 学习将本地容器push，再从远程pull

镜像、容器和虚拟机

镜像与容器

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

通过运行一个镜像来发起一个容器。镜像是一个可执行的包，包含了需要运行一个应用的所有东西，如代码、运行时间、库、环境变量以及配置文件等。

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.

容器是镜像的运行时实例。镜像被执行时，是在内存中的。

容器与虚拟机

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.

容器在Linux上本地运行，并与其他容器共享主机的内核。它运行一个离散进程，不占用任何其他可执行文件更多内存，从而使其轻巧。

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.

相反，虚拟机运行成熟的“guest”操作系统，并通过虚拟机管理程序来对主机资源进行访问。通常，VM为环境提供的资源比大多数应用程序所需要的资源更多。

准备Docker环境

测试Docker版本

    docker --version #确定docker版本
    docker info (or docker version) #查看更多细节

测试Docker安装

• 通过运行一个简单的Docker镜像（hello-world）来测试安装可工作

    docker run hello-world
    Unable to find image 'hello-world:latest' locally
    latest: Pulling from library/hello-world
    ca4f61b1923c: Pull complete
    Digest: sha256:ca0eeb6fb05351dfc8759c20733c91def84cb8007aa89a5bf606bc8b315b9fc7
    Status: Downloaded newer image for hello-world:latest
    Hello from Docker!
    This message shows that your installation appears to be working correctly.
    ...

• 列出下载到本地的hello-world镜像

    docker image ls

• 列出hello-world容器，如果容器还在运行，则不需要--all

    docker container ls --all

用Dockerfile来定义容器

• 创建一个新的文件夹，在次文件夹下新建名为Dockerfile的文件，文件内的内容如下：

# Use an official Python runtime as a parent image
FROM python:2.7-slim

# Set the working directory to /app
WORKDIR /app

# Copy the current directory contents into the container at /app
COPY . /app

# Install any needed packages specified in requirements.txt
RUN pip install --trusted-host pypi.python.org -r requirements.txt

# Make port 80 available to the world outside this container
EXPOSE 80

# Define environment variable
ENV NAME World

# Run app.py when the container launches
CMD ["python", "app.py"]

• 创建新的两个文件requirements.txt和app.py

from flask import Flask
from redis import Redis, RedisError
import os
import socket

# Connect to Redis
redis = Redis(host="redis", db=0, socket_connect_timeout=2, socket_timeout=2)

app = Flask(__name__)

@app.route("/")
def hello():
    try:
        visits = redis.incr("counter")
    except RedisError:
        visits = "cannot connect to Redis, counter disabled"

    html = "
Hello {name}!
" \
           "Hostname: {hostname}
" \
           "Visits: {visits}"
    return html.format(name=os.getenv("NAME", "world"), hostname=socket.gethostname(), visits=visits)

if __name__ == "__main__":
    app.run(host='0.0.0.0', port=80)

• 构建app
  进入到新建的文件夹后，可以看到这里有三个文件

$ ls
Dockerfile      app.py          requirements.txt

然后运行构建命令，创建一个docker镜像，使用--tag来命名

docker build --tag=friendlyhello .

• 运行app

docker run -p 4000:80 friendlyhello                   
 * Serving Flask app "app" (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: off
 * Running on http://0.0.0.0:80/ (Press CTRL+C to quit)

在浏览器中输入http://localhost:4000可以看到结果，也可以使用curl：

 curl http://localhost:4000

Hello World!
Hostname: 8fc990912a14
Visits: cannot connect to Redis, counter disabled

也可以在后台运行：

docker run -d -p 4000:80 friendlyhello

使用docker container stop来停止进程：

共享镜像

登陆Docker

$ docker login

标记镜像

docker tag image username/repository:tag

例如：

docker tag friendlyhello xiaoyaomakevin/get-started:part2

Publish镜像

docker push username/repository:tag

例如

docker push xiaoyaomakevin/get-started:part2

从远程端拉取并运行镜像

docker run -p 4000:80 username/repository:tag

例如：

docker run -p 4000:80 xiaoyaomakevin/get-started:part2
 * Serving Flask app "app" (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: off
 * Running on http://0.0.0.0:80/ (Press CTRL+C to quit)