Docker 部署一個用 Python 撰寫的 Web 應用

1. 安裝 docker

在 WSL2 中安裝 docker https://www.runoob.com/docker/ubuntu-docker-install.html
會報錯：

# Executing docker install script, commit: 93d2499759296ac1f9c510605fef85052a2c32be

WSL DETECTED: We recommend using Docker Desktop for Windows.
Please get Docker Desktop from https://www.docker.com/products/docker-desktop


You may press Ctrl+C now to abort this script.
+ sleep 20

去下載安裝 windows 下的 docker

2. 撰寫代碼

使用 Flask 框架啟動了一個 Web 服務器，而它唯一的功能是：如果當前環境中有 “NAME” 這個環境變數，就把它列印在 “Hello” 后，否則就列印 “Hello world”，最后再列印出當前環境的 hostname

import os
from flask import Flask 
import socket 
from gevent import pywsgi
app = Flask(__name__) 

@app.route('/') 
def hello(): 
    html = "<h3>Hello {name}!</h3>" \
    "<b>Hostname:</b> {hostname}<br/>" 
    return html.format(name=os.getenv("NAME", "world"), hostname=socket.gethostname()) 

if __name__ == "__main__": 
    server = pywsgi.WSGIServer(('0.0.0.0', 12345), app)
    server.serve_forever()

匯出依賴包

pip freeze >requirements.txt

Flask==2.0.1
gevent==21.8.0
greenlet==1.1.1
itsdangerous==2.0.1
Jinja2==3.0.1
MarkupSafe==2.0.1
Werkzeug==2.0.1
zope.event==4.5.0
zope.interface==5.4.0

3. 撰寫 Dockerfile

# 使用官方提供的 Python 開發鏡像作為基礎鏡像 
FROM python:3.8-slim 

# 將作業目錄切換為 /app 
WORKDIR /app 

# 將當前目錄下的所有內容復制到 /app 下 

ADD . /app

# 使用 pip 命令安裝這個應用所需要的依賴 
# RUN pip install --trusted-host pypi.python.org -r requirements.txt 
RUN pip install --trusted-host https://pypi.tuna.tsinghua.edu.cn/simple -r requirements.txt 
# 國內的源更快

# 允許外界訪問容器的 12345 埠 
EXPOSE 12345 

# 設定環境變數 
ENV NAME World 

# 設定容器行程為：python app.py，即：這個 Python 應用的啟動命令 
CMD ["python", "app.py"]
# CMD 前面 隱式的包含了 ENTRYPOINT ， /bin/sh -c

在 WSL 里操作 ：

• 讓 docker 制作鏡像，-t 加 tag，自動加載 Dockerfile，執行里面的陳述句

docker build -t helloworld .

[+] Building 17.4s (10/10) FINISHED
 => [internal] load build definition from Dockerfile                                                       0.1s
 => => transferring dockerfile: 757B                                                                       0.0s
 => [internal] load .dockerignore                                                                          0.1s
 => => transferring context: 2B                                                                            0.0s
 => [internal] load metadata for docker.io/library/python:3.8-slim                                         2.9s
 => [auth] library/python:pull token for registry-1.docker.io                                              0.0s
 => [1/4] FROM docker.io/library/python:3.8-slim@sha256:4dd66d1ccaddaa0587851cb92b365bf3090dccb41393c6f8b  0.0s
 => [internal] load build context                                                                          0.1s
 => => transferring context: 813B                                                                          0.0s
 => CACHED [2/4] WORKDIR /app                                                                              0.0s
 => [3/4] ADD . /app                                                                                       0.1s
 => [4/4] RUN pip install --trusted-host https://pypi.tuna.tsinghua.edu.cn/simple -r requirements.txt     13.6s
 => exporting to image                                                                                     0.6s
 => => exporting layers                                                                                    0.6s
 => => writing image sha256:390d32b9f7a20ccd347361bd31450807d3e63d052e334865cf8460968ffceff4               0.0s
 => => naming to docker.io/library/helloworld                                                              0.0s

Use 'docker scan' to run Snyk tests against images to find vulnerabilities and learn how to fix them

• 查看鏡像

(k8s)PC:/mnt/d/gitcode/k8s$ docker image ls
REPOSITORY   TAG       IMAGE ID       CREATED              SIZE
helloworld   latest    390d32b9f7a2   About a minute ago   169MB

• 啟動容器

docker run -p 4000:12345 helloworld

因為在 Dockerfile 中已經指定了 CMD，否則，就得把行程的啟動命令加在后面 python app.py

• 查看容器啟動

(base) $ docker ps
CONTAINER ID   IMAGE        COMMAND           CREATED         STATUS         PORTS                                         NAMES
f6e051d1af6b   helloworld   "python app.py"   2 minutes ago   Up 2 minutes   0.0.0.0:4000->12345/tcp, :::4000->12345/tcp   upbeat_elion

通過 -p 4000:12345 告訴 Docker，把容器內的 12345 埠映射在宿主機的 4000 埠上

這樣做的目的是，只要訪問宿主機的 4000 埠，就可以看到容器里應用 回傳的結果

curl http://localhost:4000
# <h3>Hello World!</h3><b>Hostname:</b> dc1c1343e366<br/>

使用容器完成了一個應用的開發與測驗

4. 上傳鏡像

注冊 docker hub，docker login 命令登錄

docker tag helloworld kobe24o/helloworld:v0

kobe24o 是賬號名（鏡像倉庫），helloworld 鏡像名，v0自己分配的版本號

docker push kobe24o/helloworld:v0

(k8s) $ docker push kobe24o/helloworld:v0
The push refers to repository [docker.io/kobe24o/helloworld]
931022d457d6: Pushing [================>                                  ]  16.07MB/47.27MB
c76dc68917fc: Pushed
047ca6dfe9ab: Pushed
d82f4c466b47: Mounted from library/python
5aa75f4e55e7: Mounted from library/python
74d6903a940b: Mounted from library/python
2f9c2b8e82bd: Mounted from library/python
ba5a5fe43301: Mounted from library/python

5. 修改鏡像

(base) $ docker ps
CONTAINER ID   IMAGE        COMMAND           CREATED         STATUS         PORTS
           NAMES
dd3bf057cb09   helloworld   "python app.py"   7 seconds ago   Up 5 seconds   0.0.0.0:4000->12345/tcp, :::4000->12345/tcp   compassionate_carver

(base) $ docker exec -it dd3bf057cb09 /bin/sh
# pwd
/app
# touch newfile.txt
# ls
Dockerfile  app.py  newfile.txt  requirements.txt
# exit

(base) $ docker commit dd3bf057cb09 kobe24o/helloworld:v1
sha256:ca8880f84040f9bdd7ef13763b9c64f8bd4a513a74bc2b095be06aae5b60268a

上面操作，新加了一個檔案到鏡像里，commit 保存

docker inspect --format '{{ .State.Pid}}' dd3bf057cb09
1763
# 查看正在運行的容器的行程號 PID 

通過查看宿主機的 proc 檔案，看到這個 行程的所有 Namespace 對應的檔案

root:/# ls -l /proc/{PID}/ns/
total 0
lrwxrwxrwx 1 root root 0 Sep 14 11:15 cgroup -> 'cgroup:[4026531835]'
lrwxrwxrwx 1 root root 0 Sep 14 11:15 ipc -> 'ipc:[4026532220]'
lrwxrwxrwx 1 root root 0 Sep 14 09:49 mnt -> 'mnt:[4026532218]'
lrwxrwxrwx 1 root root 0 Sep 14 11:15 net -> 'net:[4026531992]'
lrwxrwxrwx 1 root root 0 Sep 14 11:15 pid -> 'pid:[4026532221]'
lrwxrwxrwx 1 root root 0 Sep 14 11:15 pid_for_children -> 'pid:[4026532221]'
lrwxrwxrwx 1 root root 0 Sep 14 11:15 user -> 'user:[4026531837]'
lrwxrwxrwx 1 root root 0 Sep 14 11:15 uts -> 'uts:[4026532219]'

一個行程，可以選擇 加入 到某個行程已有的 Namespace 當中，從而達到 “進入” 這個行程所在容器的目的，這正是 docker exec 的實作原理

• push 到 hub

(base) $ docker push kobe24o/helloworld:v1
The push refers to repository [docker.io/kobe24o/helloworld]
dfee38b42dbb: Pushed
931022d457d6: Layer already exists
c76dc68917fc: Layer already exists
047ca6dfe9ab: Layer already exists
d82f4c466b47: Layer already exists
5aa75f4e55e7: Layer already exists
74d6903a940b: Layer already exists
2f9c2b8e82bd: Layer already exists
ba5a5fe43301: Layer already exists
v1: digest: sha256:7af7ff571ea9fd70d48abeaa2b38a1ed1c1a4e5a933b722d82af25d3e889f84e size: 2206