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Docker Open Source Engine Guide / Troubleshooting
Applies to SUSE Linux Enterprise Server 12 SP5

8 Troubleshooting

  

8.1 Analyze container images with container-diff

  

In case a custom Docker Open Source Engine container image built on top of the SLE base container image is not working as expected, the container-diff tool can help you analyze the image and collect information relevant for troubleshooting.

container-diff makes it possible to analyze image changes by computing differences between images and presenting the diff in a human-readable and actionable format. The tool can find differences in system packages, language-level packages, and files in a container image.

container-diff can handle local container images (using the prefix daemon:// ), images in a remote registry (using the prefix remote:// ), and images saved as .tar archives. You can use container-diff to compute the diff between a local version of an image and a remote version.

To install container-diff , run the sudo zypper in container-diff command.

8.1.1 Basic container-diff commands

  

The command container-diff analyze IMAGE runs a standard analysis on a single image. By default, it returns a hash and size of the container image. For more information that can help you to identify and fix problems, use the specific analyzers. Use the --type parameter to specify the desired analyzer. Two of the most useful analyzers are history (returns a list of descriptions of how an image layer was created) and file (returns a list of file system contents, including names, paths, and sizes): 

    tux > sudo container-diff analyze --type=history daemon://
    IMAGE
    tux > sudo container-diff analyze --type=file daemon://
    IMAGE

To view all available parameters and their brief descriptions, run the container-diff analyze --help command.

Using the container-diff diff command, you can compare two container images and examine differences between them. Similar to the container-diff analyze command, container-diff diff supports several parameters. The example command below compares two images and returns a list of descriptions of how IMAGE_2 was created from IMAGE_1. 

    tux > sudo container-diff diff daemon://
    IMAGE_1
    daemon://
    IMAGE_2
    --type=history

To view all available parameters and their brief descriptions, run the container-diff diff --help command.