Note: this library is beta and may contain bugs that prevent images from being identical to Docker build. Test your images (and add to our conformance suite)!

This library supports using the Dockerfile syntax to build Docker compatible images, without invoking Docker build. It is intended to give clients more control over how a Docker build is run, including:

• Instead of building one layer per line, run all instructions in the same container
• Set Docker HostConfig settings like network and memory controls that are not available when running Docker builds
• Mount external files into the build that are not persisted as part of the final image (i.e. "secrets")
• If there are no RUN commands in the Dockerfile, the container is created and committed, but never started.

The final image should be 99.9% compatible with regular docker builds, but bugs are always possible.

Future goals include:

• Output OCI compatible images
• Support other container execution engines, like runc or rkt
• Better conformance testing
• Port to the newer docker-engine client library
• Windows support

To download and install the library and the binary, set up a Golang build environment and with GOPATH set run:

$ go get -u github.com/openshift/imagebuilder/cmd/imagebuilder

The included command line takes one argument, a path to a directory containing a Dockerfile. The -t option can be used to specify an image to tag as:

$ imagebuilder [-t TAG] DIRECTORY

To mount a file into the image for build that will not be present in the final output image, run:

$ imagebuilder --mount ~/secrets/private.key:/etc/keys/private.key path/to/my/code testimage

Any processes in the Dockerfile will have access to /etc/keys/private.key, but that file will not be part of the committed image.

Running --mount requires Docker 1.10 or newer, as it uses a Docker volume to hold the mounted files and the volume API was not available in earlier versions. In addition, there is currently a bug that blocks Docker 1.12 from using --mount.

You can also customize which Dockerfile is run, or run multiple Dockerfiles in sequenc (the FROM is ignored on later files):

$ imagebuilder -f Dockerfile:Dockerfile.extra .

will build the current directory and combine the first Dockerfile with the second. The FROM in the second image is ignored.

f, err := os.Open("path/to/Dockerfile")
if err != nil {
	return err
}
defer f.Close()

e := builder.NewClientExecutor(o.Client)
e.Out, e.ErrOut = os.Stdout, os.Stderr
e.AllowPull = true
e.Directory = "context/directory"
e.Tag = "name/of-image:and-tag"
e.AuthFn = nil // ... pass a function to retrieve authorization info
e.LogFn = func(format string, args ...interface{}) {
	fmt.Fprintf(e.ErrOut, "--> %s\n", fmt.Sprintf(format, args...))
}

buildErr := e.Build(f, map[string]string{"arg1":"value1"})
if err := e.Cleanup(); err != nil {
	fmt.Fprintf(e.ErrOut, "error: Unable to clean up build: %v\n", err)
}

return buildErr

Example of usage from OpenShift's experimental dockerbuild command with mount secrets

go test ./dockerclient/conformance_test.go -tags conformance