Improving Docker build cache docs

[WillRy]

Improving documentation, explaining that installing dependencies within the Dockerfile can be overwritten by volumes in development environments

Description

In this section we saw the importance of layer caching to deal with dependencies when packaging the application within the container, being an ideal scenario for production environments.

But remember, in development environments most of the time the application code is shared with the container through volumes, and the code is not copied into the image through Dockerfile

In these cases, it is not recommended run your package manager (NPM, Composer, Maven, Pip, etc.) inside the image, leave the installation to CMD or ENTRYPOINT. This is important so that the volume that we will normally share when developing does not overwrite the files installed by the package manager in the Dockerfile.

Some beginners, when looking at this documentation, will believe that they should always install dependencies within the Dockerfile, which is valid for production environments and several other scenarios, but in development, volumes can overwrite the installation of dependencies made within the Dockerfile

In the current doc, has this example:

FROM node
WORKDIR /app
COPY . .          # Copy over all files in the current directory
RUN npm install   # Install dependencies
RUN npm build     # Run build

However, if the user creates a volume sharing the code within the /app directory, node_modules will be overwritten by the volume and will lose its dependencies.

I believe it is worth inserting a new section in the documentation, alerting to this difference between the treatment of dependencies in development and production when there is the presence of volumes

Currently, there are other good suggestions regarding the same problem, such as:

20450 is the link to the similar issue.

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[Luan1Schons]

Your suggestion is very useful and in agreement I also opened another pull request with the same suggestions and another point about volumes, I believe we can make the documentation more accessible about both scenarios.

PR#20450

[thompson-shaun]

/cc @dvdksn

[dvdksn]

I don't think this is the right section for this type of content.

I also think that you're better off splitting the Dockerfile into two stages instead: one stage for building the runtime image, and another stage for the dev environment.

I think that the compose section would be a more natural place for this information. @aevesdocker is there an existing page where this could fit?

[docker-robot]

Thanks for the pull request. We'd like to make our product docs better, but haven’t been able to review all the suggestions.
As our docs have also diverged, we do not have the bandwidth to review and rebase old pull requests.

If the updates are still relevant, review our contribution guidelines and rebase your pull request against the latest version of the docs, then mark it as fresh with a /remove-lifecycle stale comment.
If not, this pull request will be closed in 30 days. This helps our maintainers focus on the active pull requests.

Prevent pull requests from auto-closing with a /lifecycle frozen comment.

/lifecycle stale

[WillRy]

/lifecycle frozen

[WillRy]

/remove-lifecycle stale