Docker Image Combination: Merging Multiple Images into a Single Layer

Combining multiple Docker images into a single unified image is a feature that is not natively supported by Docker. However, the DockerMake tool, developed by an open source contributor, provides a solution to address this need.

DockerMake employs a YAML configuration file to define the composition of the target image. This file specifies the base images that contribute to the final image, along with any necessary build instructions. Consider the example scenario where you desire to create an image that includes both Java and MySQL capabilities.

Using DockerMake, you can establish a DockerMake.yml file with the following structure:

specificAB:
  requires:
    - genericA
    - genericB

genericA:
  requires:
    - customBase
  build_directory: [local directory path]
  build: |
    # Dockerfile commands for genericA
    # e.g., ADD installA.sh, RUN ./installA.sh

genericB:
  requires:
    - customBase
  build: |
    # Dockerfile commands for genericB 
    # e.g., RUN apt-get install -y genericB, ENV PATH=$PATH:something

customBase:
  FROM: debian:jessie
  build: |
    # Dockerfile commands for customBase
    # e.g., RUN apt-get update && apt-get install -y build-essentials

To build the specificAB image using DockerMake, simply execute the command:

docker-make specificAB

This command will generate the necessary Dockerfiles based on the YAML configuration and perform the build process, ultimately creating a unified image that encompasses the functionality of both Java and MySQL.