如何优化Ruby on Rails多阶段Docker镜像体积（当前632MB）

以下是针对你的Dockerfile的具体优化措施，能有效降低镜像体积：

• 替换运行时不必要的开发依赖包
  base阶段中，libpq-dev是编译PostgreSQL相关Gem所需的开发依赖，运行时只需要libpq即可。将base阶段的libpq-dev替换为libpq，减少冗余的编译类库文件。

• 安装Gem时跳过文档生成
  在bundle install命令中添加--no-document参数，避免安装Gem的文档、手册、示例等非必需内容，这能大幅缩减Gem目录的占用空间。

• 合并RUN命令减少镜像层数
  Docker每条RUN命令都会生成独立镜像层，合并用户创建、目录权限设置这类关联命令，能减少层数，间接降低镜像体积。

• 用.dockerignore排除冗余文件
  创建.dockerignore文件，排除项目中无需复制到镜像的内容，比如版本控制目录、日志、临时文件等，避免无用文件占用镜像空间。

• 深度清理Gem目录冗余内容
  在dependencies阶段，除了已有的清理步骤，额外删除Gem中的测试、示例目录，进一步压缩Gem体积。

修改后的Dockerfile #

# Dockerfile for local development.

# Default Ruby version for this project.
ARG RUBY_VERSION=3.1.0

# Base image
FROM ruby:$RUBY_VERSION-alpine AS base

# Set environment variables for the username,
# app directory, and the language.
ENV USER app
ENV APP_DIR /app

# Set env variables for dev
ENV BUNDLER_VERSION 2.3.3
ENV GEM_HOME=/usr/local/bundle
ENV BUNDLE_PATH=$GEM_HOME
ENV BUNDLE_APP_CONFIG=$BUNDLE_PATH
ENV BUNDLE_JOBS 4
ENV BUNDLE_RETRY 3
ENV RAILS_ENV development
ENV RACK_ENV development
ENV PATH=$APP_DIR/bin:$PATH
ENV LANG C.UTF-8

# 替换为运行时依赖libpq，移除开发依赖libpq-dev
RUN apk add --no-cache --update \
      libpq \
      tzdata \
      git \
    && rm -rf /var/cache/apk/*

# Start building a new image called "dependencies"
# from the "base" image.
FROM base AS dependencies

# Add libraries required for installing gems.
RUN apk add --no-cache  --update \
      build-base \
      libpq-dev \
    && rm -rf /var/cache/apk/*

# Copy the Gemfile and Gemfile.lock
# files to the current directory.
COPY Gemfile Gemfile.lock ./

# Install bundler with specified version.
RUN gem install bundler -v $BUNDLER_VERSION

# "frozen" option means that the exact versions of gems
# specified in the Gemfile.lock file will be used,
# and any updates to those gems will be ignored.
#
# Install gems with --no-document跳过文档，同时进一步清理冗余文件
RUN bundle config --global frozen 1 && \
    bundle install --no-document && \
    rm -rf $BUNDLE_PATH/cache/*.gem && \
    rm -rf $BUNDLE_PATH/ruby/*/cache && \
    find $BUNDLE_PATH/gems/ -name "*.c" -delete && \
    find $BUNDLE_PATH/gems/ -name "*.o" -delete && \
    find $BUNDLE_PATH/gems/ -name "test" -o -name "spec" -o -name "examples" | xargs rm -rf

# Start building a new image from the "base" image.
FROM base

# Copy entrypoint, make it executable.
COPY entrypoint.sh /usr/bin/
RUN chmod +x /usr/bin/entrypoint.sh
ENTRYPOINT ["entrypoint.sh"]

# 合并用户创建和目录权限设置命令，减少镜像层数
RUN adduser -D $USER && \
    mkdir -p $APP_DIR && \
    chown $USER $APP_DIR

# Set the working directory to the app directory.
WORKDIR $APP_DIR

# Switch from root to specified user.
USER $USER

# Copy the bundle directory from the "dependencies"
# image and copy all files to the current directory,
# setting the ownership to the specified user.
COPY --from=dependencies $BUNDLE_PATH $BUNDLE_PATH
COPY --chown=$USER . ./

# Expose port 3000 for the application.
EXPOSE 3000

# Run the command to start the Rails server.
CMD ["rails", "s", "-b", "0.0.0.0"]

配套的.dockerignore文件 #

.git/
log/
tmp/
node_modules/
.gitignore
.DS_Store
*.log

内容的提问来源于stack exchange，提问作者etranz