Docker: Combine multiple images

Question

Is it possible with Docker to combine two images into one?

Like this here:

genericA --
            \
             ---> specificAB
            /
genericB --

For example there's an image for Java and an image for MySQL.

I'd like to have an image with Java and MySQL.

Answer 1

You can put multiple FROM commands in a single Dockerfile.

https://docs.docker.com/reference/builder/#from

Answer 2

Docker doesn't directly support this, but you can use DockerMake (full disclosure: I wrote it) to manage this sort of "inheritance". It uses a YAML file to set up the individual pieces of the image, then drives the build by generating the appropriate Dockerfiles.

Here's how you would build this slightly more complicated example:

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

You would use this DockerMake.yml file:

specificAB:
  requires:
    - genericA
    - genericB

genericA:
  requires:
     - customBase
  build_directory: [some local directory]
  build: |
    #Dockerfile commands go here, such as
    ADD installA.sh
    RUN ./installA.sh

genericB:
  requires:
    - customBase
  build: |
    #Here are some other commands you could run
    RUN apt-get install -y genericB
    ENV PATH=$PATH:something

customBase:
  FROM: debian:jessie
  build: |
    RUN apt-get update && apt-get install -y buildessentials

After installing the docker-make CLI tool (pip install dockermake), you can then build the specificAB image just by running

docker-make specificAB

Answer 3

No, you can only inherit from one image.

You probably don't want Java and MySQL in the same image as it's more idiomatic to have a single component in a container i.e. create a separate MySQL container and link it to the Java container rather than put both into the same container.

However, if you really must have them in the same image, write a Dockerfile with Java as the base image (FROM statement) and install MySQL in the Dockerfile. You should be able to largely copy the statements from the official MySQL Dockerfile.

Answer 4

If you do docker commit, it is not handy to see what commands were used in order to build your container, you have to issue a docker history image

If you have a Dockerfile, just look at it and you see how it was built and what it contains.

Docker commit is 'by hand', so prone to errors, docker build using a Dockerfile that works is much better.