Scaffolded .dockerignore does not do what it claims

[busser]

When running make docker-build for an operator scaffolded with kubebuilder v3, the entire directory is included in the Docker build context.

I expected only Go source files to be included in the Docker build context. Here is the scaffolded .dockerignore file:

# More info: https://docs.docker.com/engine/reference/builder/#dockerignore-file
# Ignore all files which are not go type
!**/*.go
!**/*.mod
!**/*.sum

To reproduce, build a dummy Docker image containing the entire build context:

docker image build -t build-context -f - . <<EOF
FROM busybox
COPY . /build-context
WORKDIR /build-context
CMD find .
EOF

Now run it:

docker container run --rm build-context

Or explore the images contents:

docker container run --rm -it build-context /bin/sh

I've traced the issue to this source code:

kubebuilder/pkg/plugins/golang/v3/scaffolds/internal/templates/dockerignore.go

Lines 41 to 46 in 2018a4f

	const dockerignorefileTemplate = `# More info: https://docs.docker.com/engine/reference/builder/#dockerignore-file
	# Ignore all files which are not go type
	!**/*.go
	!**/*.mod
	!**/*.sum
	`

For reference, this is my Docker version:

Client: Docker Engine - Community
 Cloud integration: 1.0.7
 Version:           20.10.2
 API version:       1.41
 Go version:        go1.13.15
 Git commit:        2291f61
 Built:             Mon Dec 28 16:12:42 2020
 OS/Arch:           darwin/amd64
 Context:           default
 Experimental:      true

Server: Docker Engine - Community
 Engine:
  Version:          20.10.2
  API version:      1.41 (minimum version 1.12)
  Go version:       go1.13.15
  Git commit:       8891c58
  Built:            Mon Dec 28 16:15:28 2020
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.4.3
  GitCommit:        269548fa27e0089a8b8278fc4fc781d7f65a939b
 runc:
  Version:          1.0.0-rc92
  GitCommit:        ff819c7e9184c13b7c2607fe6c30ae19403a7aff
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

/kind bug

[busser]

It seems to me that the .dockerignore file has unexpected behavior. It does not handle a directory wildcard ** properly when it is right after an exclamation !.

For instance, If I replace the .dockerignore's contents with these:

# More info: https://docs.docker.com/engine/reference/builder/#dockerignore-file
# Ignore all files which are not go type
*
!**/*.go

The contents of the controllers/ directory are not included in the Docker build context. However, with this .dockerignore file:

# More info: https://docs.docker.com/engine/reference/builder/#dockerignore-file
# Ignore all files which are not go type
*
!controllers/**/*.go

The Go files in the controllers/ are properly included.

[busser]

I figure that the easiest way to work around this issue is to change the scaffolded .dockerignore file to ignore all files except those referenced in the scaffolded Dockerfile. The .dockerignore file would thus contain:

# More info: https://docs.docker.com/engine/reference/builder/#dockerignore-file
# Ignore all files which are not go type
*
!go.mod
!go.sum
!main.go
!controllers/**/*.go
!api/**/*.go

If that's OK with you, I can open a PR to make the change.

[camilamacedo86]

It is great. Please, feel free to collab with the solution.

[fejta-bot]

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