Docker技术笔记：Docker入门浅尝

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