为什么在 dockerfile 卷上挂载时 emptydir 不为空？

Question

出于各种原因（主要是我懒惰）我想将我的 wordpress 文件挂载到 /var/www/html/blog 而不是 /var/www/html 然后使用 sidecar 模式来拥有 nginx 和wordpress-fpm 共享一个目录。我将一个空目录安装到 /var/www/html 我希望它是空的（Duh！），然后将我的文件复制到 /var/www/html/blog

我的 Dockerfile：

FROM wordpress:5.7.2-fpm-alpine
LABEL author="wayne@...co.uk"

COPY public/wordpress /app/blog

Wordpress 的 dockerfile：

#
# NOTE: THIS DOCKERFILE IS GENERATED VIA "apply-templates.sh"
#
# PLEASE DO NOT EDIT IT DIRECTLY.
#

FROM php:7.4-fpm-alpine

# persistent dependencies
RUN set -eux; \
    apk add --no-cache \
# in theory, docker-entrypoint.sh is POSIX-compliant, but priority is a working, consistent image
        bash \
# BusyBox sed is not sufficient for some of our sed expressions
        sed \
# Ghostscript is required for rendering PDF previews
        ghostscript \
# Alpine package for "imagemagick" contains ~120 .so files, see: https://github.com/docker-library/wordpress/pull/497
        imagemagick \
    ;

# install the PHP extensions we need (https://make.wordpress.org/hosting/handbook/handbook/server-environment/#php-extensions)
RUN set -ex; \
    \
    apk add --no-cache --virtual .build-deps \
        $PHPIZE_DEPS \
        freetype-dev \
        imagemagick-dev \
        libjpeg-turbo-dev \
        libpng-dev \
        libzip-dev \
    ; \
    \
    docker-php-ext-configure gd \
        --with-freetype \
        --with-jpeg \
    ; \
    docker-php-ext-install -j "$(nproc)" \
        bcmath \
        exif \
        gd \
        mysqli \
        zip \
    ; \
    pecl install imagick-3.4.4; \
    docker-php-ext-enable imagick; \
    rm -r /tmp/pear; \
    \
    runDeps="$( \
        scanelf --needed --nobanner --format '%n#p' --recursive /usr/local/lib/php/extensions \
            | tr ',' '\n' \
            | sort -u \
            | awk 'system("[ -e /usr/local/lib/" $1 " ]") == 0 { next } { print "so:" $1 }' \
    )"; \
    apk add --no-network --virtual .wordpress-phpexts-rundeps $runDeps; \
    apk del --no-network .build-deps

# set recommended PHP.ini settings
# see https://secure.php.net/manual/en/opcache.installation.php
RUN set -eux; \
    docker-php-ext-enable opcache; \
    { \
        echo 'opcache.memory_consumption=128'; \
        echo 'opcache.interned_strings_buffer=8'; \
        echo 'opcache.max_accelerated_files=4000'; \
        echo 'opcache.revalidate_freq=2'; \
        echo 'opcache.fast_shutdown=1'; \
    } > /usr/local/etc/php/conf.d/opcache-recommended.ini
# https://wordpress.org/support/article/editing-wp-config-php/#configure-error-logging
RUN { \
# https://www.php.net/manual/en/errorfunc.constants.php
# https://github.com/docker-library/wordpress/issues/420#issuecomment-517839670
        echo 'error_reporting = E_ERROR | E_WARNING | E_PARSE | E_CORE_ERROR | E_CORE_WARNING | E_COMPILE_ERROR | E_COMPILE_WARNING | E_RECOVERABLE_ERROR'; \
        echo 'display_errors = Off'; \
        echo 'display_startup_errors = Off'; \
        echo 'log_errors = On'; \
        echo 'error_log = /dev/stderr'; \
        echo 'log_errors_max_len = 1024'; \
        echo 'ignore_repeated_errors = On'; \
        echo 'ignore_repeated_source = Off'; \
        echo 'html_errors = Off'; \
    } > /usr/local/etc/php/conf.d/error-logging.ini

RUN set -eux; \
    version='5.7.2'; \
    sha1='c97c037d942e974eb8524213a505268033aff6c8'; \
    \
    curl -o wordpress.tar.gz -fL "https://wordpress.org/wordpress-$version.tar.gz"; \
    echo "$sha1 *wordpress.tar.gz" | sha1sum -c -; \
    \
# upstream tarballs include ./wordpress/ so this gives us /usr/src/wordpress
    tar -xzf wordpress.tar.gz -C /usr/src/; \
    rm wordpress.tar.gz; \
    \
# https://wordpress.org/support/article/htaccess/
    [ ! -e /usr/src/wordpress/.htaccess ]; \
    { \
        echo '# BEGIN WordPress'; \
        echo ''; \
        echo 'RewriteEngine On'; \
        echo 'RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]'; \
        echo 'RewriteBase /'; \
        echo 'RewriteRule ^index\.php$ - [L]'; \
        echo 'RewriteCond %{REQUEST_FILENAME} !-f'; \
        echo 'RewriteCond %{REQUEST_FILENAME} !-d'; \
        echo 'RewriteRule . /index.php [L]'; \
        echo ''; \
        echo '# END WordPress'; \
    } > /usr/src/wordpress/.htaccess; \
    \
    chown -R www-data:www-data /usr/src/wordpress; \
# pre-create wp-content (and single-level children) for folks who want to bind-mount themes, etc so permissions are pre-created properly instead of root:root
# wp-content/cache: https://github.com/docker-library/wordpress/issues/534#issuecomment-705733507
    mkdir wp-content; \
    for dir in /usr/src/wordpress/wp-content/*/ cache; do \
        dir="$(basename "${dir%/}")"; \
        mkdir "wp-content/$dir"; \
    done; \
    chown -R www-data:www-data wp-content; \
    chmod -R 777 wp-content

VOLUME /var/www/html

COPY --chown=www-data:www-data wp-config-docker.php /usr/src/wordpress/
COPY docker-entrypoint.sh /usr/local/bin/

ENTRYPOINT ["docker-entrypoint.sh"]
CMD ["php-fpm"]

我的部署

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: wordpress
spec:
  replicas: 1
  strategy:
    rollingUpdate:
      maxSurge: 25%
      maxUnavailable: 25%
    type: RollingUpdate
  selector:
    matchLabels:
      app: wordpress
  revisionHistoryLimit: 5
  template: 
    metadata:
      labels:
        app: wordpress
    spec:
      volumes:
        - name: shared
          emptyDir: {}
      containers:
        - name: nginx
          image: nginx
          volumeMounts:
            - name: shared
              mountPath: /var/www/html
        - name: wordpress
          image: redacted/imagename:0.0.1
          volumeMounts:
            - name: shared
              mountPath: /var/www/html
          # Important! After this container has started, the PHP files
          # in our Docker image aren't in the shared volume. 
          # If we tried to write directly to this volume from our Docker image
          #  the files wouldn't appear in the nginx container.
          # So, after the container has started, copy the PHP files from this
          # container's local filesystem
          lifecycle:
            postStart:
              exec:
                command: ["/bin/sh", "-c", "cp -r /app/. /var/www/html"]
      imagePullSecrets:
      - name: regcred

现在奇怪的地方来了……系好安全带……

当我 kubectl exec 进入容器并列出 /var/www/html 的内容时，我得到：

/var/www/html# ls
blog         readme.html      wp-blog-header.php    wp-content   wp-links-opml.php  wp-mail.php      wp-trackback.php
index.php    wp-activate.php  wp-comments-post.php  wp-cron.php  wp-load.php        wp-settings.php  xmlrpc.php
license.txt  wp-admin         wp-config-sample.php  wp-includes  wp-login.php       wp-signup.php

有我的博客文件夹，但也有大量的 wordpress 文件，就像它已将文件从 /var/lib/docker/volumes 复制到我的 emptydir... 但这不是文档所说的 emptydir 应该如何工作。文档说：

空目录

emptyDir 卷是在将 Pod 分配给节点时首先创建的，并且只要该 Pod 在该节点上运行就存在。顾名思义，emptyDir 卷最初是空的。 Pod 中的所有容器都可以在 emptyDir 卷中读取和写入相同的文件，尽管该卷可以安装在每个容器中相同或不同的路径上。当 Pod 因任何原因从节点中移除时，emptyDir 中的数据将被永久删除。

所以最后我的问题......那么这里发生了什么？？？

Answer 1

您从Docker Hub wordpress image 开始，其中有its Docker image setup in GitHub。

重要的细节是Dockerfile 以

结尾

ENTRYPOINT ["docker-entrypoint.sh"]
CMD ["php-fpm"]

这是使用 shell 脚本作为包装器进行首次设置并为其提供实际运行命令的标准模式 (Docker passes the CMD as arguments to the ENTRYPOINT)。 Wordpress image docker-entrypoint.sh 又具有片段：

if [ ! -e index.php ] && [ ! -e wp-includes/version.php ]; then
  echo >&2 "WordPress not found in $PWD - copying now..."
  ...
  for contentPath in \
    /usr/src/wordpress/.htaccess \
    /usr/src/wordpress/wp-content/*/*/ \
  ; do
    ...
  done
  tar cf - ... . | tar xf -
fi

该片段查看当前目录；如果它没有index.php 文件，它会复制/usr/src/wordpress 那里。这将在容器启动时、在任何卷已安装之后以及在您的 postStart 钩子触发之前运行。

您可以通过将自己的内容复制到 Wordpress 基础树中来利用此设置，而不是设置单独的挂钩：

FROM wordpress:5.7.2-fpm-alpine
COPY public/wordpress /usr/src/wordpress/blog