Docker——初级学习
标签：docker
学习内容
- 学习镜像、容器和虚拟机的区别
- 学习使用Dockerfile来定义一个容器
- 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 = "<i>cannot connect to Redis, counter disabled</i>"
html = "<h3>Hello {name}!</h3>" \
"<b>Hostname:</b> {hostname}<br/>" \
"<b>Visits:</b> {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
<h3>Hello World!</h3><b>Hostname:</b> 8fc990912a14<br/><b>Visits:</b> <i>cannot connect to Redis, counter disabled</i>
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)
