Combining Multiple Docker Images

Combining multiple Docker images into a single, unified image is not directly supported by Docker. However, there are third-party tools available to facilitate this process. DockerMake is one such tool that enables the creation of complex image inheritance scenarios.

Using DockerMake to Combine Images

DockerMake operates by utilizing a YAML file to define the relationships between Docker images. Based on the YAML configuration, DockerMake generates Dockerfiles that guide the build process.

For instance, to combine a Java and MySQL image into a new image named "specificAB," you would create a DockerMake.yml file as follows:

specificAB:
  requires:
    - genericA
    - genericB

genericA:
  requires:
    - customBase
  build_directory: [a local directory]
  build: |
    # Dockerfile commands specific to genericA

genericB:
  requires:
    - customBase
  build: |
    # Dockerfile commands specific to genericB

customBase:
  FROM: Debian:jessie
  build: |
    # Dockerfile commands to set up the base image

This configuration establishes the following inheritance structure:

                                 --> genericA --
                                /                \
  debian:jessie -->  customBase                   ---> specificAB
                                \                /
                                  --> genericB --

Building the Combined Image

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

docker-make specificAB

Conclusion

While Docker does not directly provide a built-in mechanism to combine images, DockerMake offers a convenient and powerful solution to achieve this functionality. By defining complex inheritance scenarios in a YAML file, DockerMake streamlines the process of creating and managing combined Docker images.