multidockerfile

multidockerfile is a command-line tool that allows you to split multi-stage Dockerfiles into multiple files.

Background

Multi-stage builds are a powerful way to optimize Dockerfiles, especially when combined with docker buildx bake to build multiple images in parallel. However, Docker requires that all stages are defined in a single Dockerfile, which can become difficult to navigate as it grows.

With multidockerfile, you can split the Dockerfile up, and recombine it with multidockerfile join before building the images.

multidockerfile parses the individual Dockerfiles looking for the FROM and COPY --from instructions that create dependencies between stages. The combined Dockerfile is sorted so that stages with dependencies appear after the stages on which they depend.

Installation

From binary releases

Pre-built binaries are available for each release. You can download the correct version for your operating system, make it executable with chmod +x, and either execute it directly or put it on your path.

SHA-256 checksums and GPG signatures are available to verify integrity. My GPG public key can be obtained from

GitHub (@haines)

$ curl https://github.com/haines.gpg | gpg --import

Keybase (haines)

$ curl https://keybase.io/haines/pgp_keys.asc | gpg --import

keys.openpgp.net (andrew@haines.org.nz)

$ gpg --keyserver keys.openpgp.org --recv-keys 6E225DD62262D98AAC77F9CDB16A6F178227A23E

With Docker

A Docker image is available for each release at ghcr.io/haines/multidockerfile.

Usage

multidockerfile join <inputs> ...

Join multiple Dockerfiles into a single multi-stage Dockerfile.

Arguments

Name	Description
<inputs> ...	Paths to the Dockerfiles to be joined.

Options

Short	Long	Default	Description
-o	--output	-	Where to write the multi-stage Dockerfile (- for stdout).

Example

# dockerfiles/one.dockerfile

FROM alpine AS one

# dockerfiles/two.dockerfile

FROM alpine AS two

$ multidockerfile join dockerfiles/*.dockerfile
FROM alpine AS one
FROM alpine AS two

multidockerfile version

Show the multidockerfile version information.

Example

$ multidockerfile version
{
  "Version": "0.1.0-dev",
  "GitCommit": "20586c3eb00aad3dde1ca63eb47dcb14ae6372d5",
  "Built": "2021-02-26T21:22:04Z",
  "GoVersion": "go1.16",
  "OS": "darwin",
  "Arch": "amd64"
}