Docker技术笔记：Docker入门浅尝

た入场券 2022-05-29 05:40 182阅读 0赞

# 简介 #

本文将用Docker的方式来构建一个应用APP。

过去，如果要开发一个Python应用APP，所需做的第一件事就是在开发机上安装Python运行时环境。在这种情形下，开发机的环境必须与APP所要求的环境一致，同时还需要与生产环境相匹配。

通过使用Docker，可以将一个可移植的Python运行时环境作为一个image获取，而无需安装。然后，就可以基于Python运行时环境image，将APP代码及其依赖库合并构建，从而简化了应用APP的部署难度。

# 用Dockerfile定义容器Container #

Dockerfile是由一系列命令和参数构成的脚本，这些命令应用于基础镜像并最终创建一个新的镜像。它简化了业务部署的流程，大大提高了业务的部署速度。Dockerfile的产出为一个新的可以用于创建容器的镜像。

Dockerfile语法由两部分构成，分别是“注释”和“命令+参数”。

# Line blocks used for commenting
    COMMAND argument1 argument2 ...

对于Dockerfile，我们首先创建一个空目录，然后cd到该目录，并创建Dockerfile文件。

# 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
    ADD . /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"]

其中，app.py和requirements.txt都位于与Dockerfile相同的目录下，具体如下：

zjl@ubuntu:~/docker/pyapp$ ls
    app.py  Dockerfile  requirements.txt

对于requirements.txt，其内容如下：

Flask
    Redis

对于app.py，其内容如下：

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

现在，我们知道，`pip install -r requirements.txt`为Python安装了Flask和Redis库，同时APP会打印出环境变量`NAME`，同时将`socket.gethostname()`打印出来。

# 构建新的image镜像 #

下面，我们进行构建，具体如下：

zjl@ubuntu:~/docker/pyapp$ ls
    app.py  Dockerfile  requirements.txt
    
    zjl@ubuntu:~/docker/pyapp$ sudo docker build -t fhello .
    Sending build context to Docker daemon  4.608kB
    Step 1/7 : FROM python:2.7-slim
    2.7-slim: Pulling from library/python
    d2ca7eff5948: Pull complete 
    cef69dd0e5b9: Pull complete 
    50e1d7e4f3c6: Pull complete 
    861e9de5333f: Pull complete 
    Digest: sha256:e9baca9b405d3bbba71d4c3c4ce8a461e4937413b8b910cb1801dfac0a2423aa
    Status: Downloaded newer image for python:2.7-slim
     ---> 52ad41c7aea4
    Step 2/7 : WORKDIR /app
    ...
    Step 3/7 : ADD . /app
    ...
    Step 4/7 : RUN pip install --trusted-host pypi.python.org -r requirements.txt
    ...
    Step 5/7 : EXPOSE 80
    ...
    Step 6/7 : ENV NAME World
    ...
    Step 7/7 : CMD ["python", "app.py"]
    ...
    Successfully built d3fafd68e807
    Successfully tagged fhello:latest
    
    zjl@ubuntu:~/docker/pyapp$ sudo docker image ls
    REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
    fhello              latest              12d000cd7a1b        12 minutes ago      148MB

# 运行新的image镜像 #

$ sudo docker run -p 4000:80 fhello
     * Running on http://0.0.0.0:80/ (Press CTRL+C to quit)
    
    # 访问该网站
    $ curl localhost:4000
    <h3>Hello World!</h3><b>Hostname:</b> f4e37f061593<br/><b>Visits:</b> <i>cannot connect to Redis, counter disabled</i>
    
    $ sudo docker container ls
    CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS                  NAMES
    4a150bdc67cd        fhello              "python app.py"     10 seconds ago      Up 9 seconds        0.0.0.0:4000->80/tcp   upbeat_austin

关闭容器，命令如下：

$ sudo docker container stop 4a150bdc67cd
    4a150bdc67cd

# 给镜像打上标签 #

syntax: -->> docker tag image username/repository:tag
    
     $ sudo docker tag fhello zhjl/getstarted:alpha-1 $ sudo docker image ls REPOSITORY TAG IMAGE ID CREATED SIZE fhello latest 12d000cd7a1b 18 minutes ago 148MB zhjl/getstarted alpha-1 12d000cd7a1b 18 minutes ago 148MB $ docker run -p 4000:80 zhjl/getstarted:alpha-1

# Recap and cheat sheet #

# Create image using this directory's Dockerfile
    docker build -t fhello .
    
    # Run "friendlyname" mapping port 4000 to 80
    docker run -p 4000:80 fhello
    
    # Same thing, but in detached mode
    docker run -d -p 4000:80 fhello
    
    # List all running containers
    docker container ls
    
    # List all containers, even those not running
    docker container ls -a
    
    # Gracefully stop the specified container
    docker container stop <hash>
    
    # Force shutdown of the specified container
    docker container kill <hash>
    
    # Remove specified container from this machine
    docker container rm <hash>
    
    # Remove all containers
    docker container rm $(docker container ls -a -q)
    
    # List all images on this machine
    docker image ls -a
    
    # Remove specified image from this machine
    docker image rm <image id>
    
    # Remove all images from this machine
    docker image rm $(docker image ls -a -q)
    
    # Log in this CLI session using your Docker credential
    docker login
    
    # Tag <image> for upload to registry
    docker tag <image> username/repository:tag
    
    # Upload tagged image to registry
    docker push username/repository:tag
    
    # Run image from a registry
    docker run username/repository:tag