docker-compose 無法等待 mysql 數據庫

Question

我在嘗試使用 docker-compose 腳本來啟動 mysql 數據庫和 Django 項目時遇到了真正的問題，但是讓 Django 項目等待 mysql 數據庫准備就緒。

我有兩個文件，一個 Dockerfile 和一個 docker-compose.yml，我在下面復制了它們。

當我運行 docker-compose.yml 並檢查 Web 容器的日志時，它說它無法連接到數據庫 mydb。 然而，我第二次運行它（沒有清除容器和圖像）它正確連接並且 Django 應用程序工作。

我花了一整天的時間嘗試了很多東西，比如腳本、健康檢查等，但我無法讓它工作。

文件

FROM python:3.6

ENV PYTHONUNBUFFERED 1

RUN mkdir /code
WORKDIR /code

COPY ./ /code/

RUN pip install -r requirements.txt
RUN python manage.py collectstatic --noinput

docker-compose.yml

version: '3'

services:
  mydb:
    environment:
      - MYSQL_ROOT_PASSWORD=password
      - MYSQL_USER=django
      - MYSQL_PASSWORD=secret
      - MYSQL_DATABASE=dbMarksWebsite
    image: mysql:5.7
    ports:
      # Map default mysql port 3306 to 3308 on outside so that I can connect
      # to mysql using workbench localhost with port 3308
      - "3308:3306"
  web:
    environment:
      - DJANGO_DEBUG=1
      - DOCKER_PASSWORD=secret
      - DOCKER_USER=django
      - DOCKER_DB=dbMarksWebsite
      - DOCKER_HOST=mydb
      - DOCKER_PORT=3306
    build: .
    command: >
      sh -c "sleep 10 &&
             python manage.py migrate &&
             python manage.py loaddata myprojects_testdata.json &&
             python manage.py runserver 0.0.0.0:8080"
    ports:
      - "8080:8080"
    depends_on:
      - mydb

第一次運行（沒有現有的圖像或容器）：

...
  File "/usr/local/lib/python3.6/site-packages/MySQLdb/__init__.py", line 84, in Connect
    return Connection(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/MySQLdb/connections.py", line 179, in __init__
    super(Connection, self).__init__(*args, **kwargs2)
django.db.utils.OperationalError: (2002, "Can't connect to MySQL server on 'mydb' (115)")

第二次運行：

System check identified no issues (0 silenced).
March 27, 2020 - 16:44:57
Django version 2.2.11, using settings 'ebdjango.settings'
Starting development server at http://0.0.0.0:8080/
Quit the server with CONTROL-C.

Answer 1

對於任何感興趣的人，我找到了解決方案：

1 - 我寫了一個 python 腳本來每秒連接到數據庫，但有超時。 我將此超時設置為相當高的 60 秒，但這似乎適用於我的計算機。

2 - 我在我的撰寫文件中添加了等待命令。

這應該意味着我可以為我的網站提供一組測試容器，我可以在其中指定所使用的 Python 和 MySQL 的確切版本。

相關文件如下：

Dockerfile：

FROM python:3.6

ENV PYTHONUNBUFFERED 1

RUN mkdir /code
WORKDIR /code

COPY ./ /code/

RUN pip install -r requirements.txt
RUN python manage.py collectstatic --noinput

docker-compose.yml

version: '3'

services:
  mydb:
    container_name: mydb
    environment:
      - MYSQL_ROOT_PASSWORD=password
      - MYSQL_USER=django
      - MYSQL_PASSWORD=secret
      - MYSQL_DATABASE=dbMarksWebsite
    image: mysql:5.7
    ports:
      # Map default mysql port 3306 to 3308 on outside so that I can connect
      # to mysql using workbench localhost with port 3308
      - "3308:3306"
  web:
    container_name: web
    environment:
      - DJANGO_DEBUG=1
      - DOCKER_PASSWORD=secret
      - DOCKER_USER=django
      - DOCKER_DB=dbMarksWebsite
      - DOCKER_HOST=mydb
      - DOCKER_PORT=3306
    build: .
    command: >
      sh -c "python ./bin/wait-for.py mydb 3306 django secret dbMarksWebsite 60  &&
             python manage.py migrate &&
             python manage.py loaddata myprojects_testdata.json &&
             python manage.py runserver 0.0.0.0:8080"
    ports:
      - "8080:8080"
    depends_on:
      - mydb

等待.py

'''
I don't like adding this in here, but I cannot get the typical wait-for scripts
to work with MySQL database in docker, so I hve written a python script that
either times out after ? seconds or successfully connects to the database
The input arguments for the script need to be:

    HOST, PORT, USERNAME, PASSWORD, DATABASE, TIMEOUT

'''
import sys, os
import time
import pymysql

def readCommandLineArgument():
    '''
    Validate the number of command line input arguments and return the
    input filename
    '''

    # Get arguments
    if len(sys.argv)!=7:
        raise ValueError("You must pass in 6 arguments, HOST, PORT, USERNAME, PASSWORD, DATABASE, TIMEOUT")

    # return the arguments as a tuple
    return (sys.argv[1], sys.argv[2], sys.argv[3], sys.argv[4], sys.argv[5], sys.argv[6]) 

def connectToDB(HOST, PORT, USERNAME, PASSWORD, DATABASE):
    '''
    for now, just try to connect to the database.
    '''

    con = pymysql.connect(host=HOST, port=PORT, user=USERNAME, password=PASSWORD, database=DATABASE)

    with con:
        cur = con.cursor()
        cur.execute("SELECT VERSION()")

def runDelay():
    '''
    I don't like passing passwords in, but this is only used for a test docker
    delay script
    '''

    # Get the database connection characteristics.
    (HOST, PORT, USERNAME, PASSWORD, DATABASE, TIMEOUT) = readCommandLineArgument()

    # Ensure timeout is an integer greater than zero, otherwise use 15 secs a default
    try:
        TIMEOUT = int(TIMEOUT)
        if TIMEOUT <= 0:
            raise("Timeout needs to be > 0")
    except:
        TIMEOUT = 60

    # Ensure port is an integer greater than zero, otherwise use 3306 as default
    try:
        PORT = int(PORT)
        if PORT <= 0:
            raise("Port needs to be > 0")
    except:
        PORT = 3306

    # Try to connect to the database TIMEOUT times
    for i in range(0, TIMEOUT):

        try:
            # Try to connect to db
            connectToDB(HOST, PORT, USERNAME, PASSWORD, DATABASE)

            # If an error hasn't been raised, then exit
            return True

        except Exception as Ex:
            strErr=Ex.args[0]
            print(Ex.args)
            # Sleep for 1 second
            time.sleep(1)

    # If I get here, assume a timeout has occurred
    raise("Timeout")


if __name__ == "__main__":

    runDelay()

Answer 2

出於測試/開發目的，您可以使用具有運行狀況檢查的 MySQL 映像版本（我相信有一個healthcheck/mysql映像），或配置您自己的（請參見此處的示例： Docker-compose check if mysql connection is ready ）。

對於生產用途，您不想在啟動時升級數據庫架構，也不想假設數據庫已啟動。 升級架構會自動鼓勵您不要考慮部署錯誤並需要回滾時會發生什么，並且並行架構升級將不起作用。 更長的版本： https : //pythonspeed.com/articles/schema-migrations-server-startup/

Answer 3

我在 entrypoint.sh 中使用以下函數解決了它：

function wait_for_db()
{
  while ! ./manage.py sqlflush > /dev/null 2>&1 ;do
    echo "Waiting for the db to be ready."
    sleep 1
  done
}

Answer 4

另一種選擇是使用腳本來控制啟動順序，並包裝 Web 服務的命令。

在docker-compose 的文檔中， “ wait-for-it ”是推薦的工具之一，但也存在其他工具。