Docker - CMD npm start 先于复制所有

Question

我正在浏览 Docker 的官方 getting started guide ，还有一部分我不确定:

末Dockerfile CMD [ "npm", "start" ]写在COPY . .之前，难道不应该反过来吗？ Node.js Dockerfile documentation有不同的顺序

# Use the official image as a parent image.
FROM node:current-slim

# Set the working directory.
WORKDIR /usr/src/app

# Copy the file from your host to your current location.
COPY package.json .

# Run the command inside your image filesystem.
RUN npm install

# Inform Docker that the container is listening on the specified port at runtime.
EXPOSE 8080

# Run the specified command within the container.
CMD [ "npm", "start" ]

# Copy the rest of your app's source code from your host to your image filesystem.
COPY . .

Answer 1

CMD 位于何处实际上并不重要。生成容器时，它将保留由 docker 执行的命令。

由于文件夹的内容不会影响图像内部的步骤，因此将其作为最后一个可用步骤以最佳使用缓存是有意义的(即使它并没有真正影响那里)。