Location for common .dockerignore file

Question

I'd like a common .dockerignore file, "outside" a build context (which I assume is the directory in which the Dockerfile is located).

So instead of this:

project/
  client/
      src/
      .dockerignore
      Dockerfile
  server/
      src/
      .dockerignore
      Dockerfile

I prefer this:

project/
  client/
      src/
      Dockerfile
  server/
      src/
      Dockerfile
  .dockerignore

Is that allowed? Will it walk up the filesystem until root, looking for an ignore file (the way it's commonly done by other cli tools), or must it be at the same level as the Dockerfile?

There have been changes to the mechanism in recent docker versions, e.g. for custom Dockerfile.foo.dockerignore files, which must be placed at the same level as the Dockerfile.foo. So I'm unsure what is the current rule, and the docs don't explain.

I'm using the latest version, docker 24.0.5.

Answer 1

From your docs link:

Before the docker CLI sends the context to the docker daemon, it looks for a file named .dockerignore in the root directory of the context.

From build context:

The build context is the argument that you pass to the build command. When your build context is a local directory, a remote Git repository, or a tar file, then that becomes the set of files that the builder can access during the build.

From docker build:

By default the docker build command will look for a Dockerfile at the root of the build context. The -f, --file, option lets you specify the path to an alternative file to use instead.

So you should be able to do:

docker build -f client <path_to_project>

Something to keep in mind using this approach: If you have only one .dockerignore file you wont be able to exclude the source code for the other builds. As a result the source code for all builds will be sent to the docker daemon in each individual build. So be careful that you are not sending large amounts of data.