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Docker image is getting bigger and bigger – Debian

right now I’m experimenting with Docker.

I have "installed" a Docker Debian Image.
In this Debian Environment, I installed a application.

Now, I do every night this:

  • docker stop (stop container)
  • docker commit (make container to an
    image)
  • docker save (to save the image to an file, I do this to backup
    the current work)
  • docker run (to start the container)

So as you can see, I try to create a "backup-solution".

It works perfectly. But the problem is, that the backup-files are getting bigger and bigger by every day.
Even without touchting the container for multiple days.

It used to be well under 10 gigabytes, but now it’s already 20.

Why is that? What am I doing wrong?

Thanks a lot

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3

Answers


  1. 0

    Docker images save "diffs" every commit you make, along with all previous versions of your image. This means that your process is guaranteed to steadily increase your final image size. To avoid this, instead of using docker save, you should use docker export instead (which receives the container as an argument, instead of an image).

    Docker save

    Docker export

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  2. 0

    Using docker commit usually isn’t a best practice. The Dockerfile system described in places like Docker’s Build and run your image tutorial will let you write a file that lists out all of the commands that need to be run to build the image. You can check that file into source control, and run docker build whenever you need to recreate the image.

    If the Dockerfile is checked in alongside the source code to your application, you can check out old versions of your application source and re-docker build the image from there. There’s not a particular need to save binary copies of images.

    At a technical level, the images docker commit creates always consist of the original image, plus an additional layer that’s whatever changed in the container. If you repeatedly docker commit each image will always be larger than the image before it, even if you delete or overwrite files. (Typical Docker images are under 1 GB, and depending on the application runtime and base image, are frequently in the 100-200 MB range.)

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  3. 0

    I had the same problem until I figured out it’s because after docker save the image tar file was generated in the same folder.

    Next time when it’s built again, the tar file is included inside the next image as well.

    After added *.tar in my .dockerignore now it’s working fine.

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