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Containerdiff

Tool to show changes among two container images.

Example usage

We want to compare two docker images. For this example lets choose CentOS docker images. So we have two images:

docker.io/centos:7.1.1503 , docker.io/centos:7.2.1511

and we want to know what is different in 7.2 according to 7.1 image.

Containerdiff tool now supports these tests:

  • changes in installed RPM packages
  • changes in files not installed by RPM
  • changes in container image metadata
  • changes in container image history

First we have to pull images.

$ docker pull docker.io/centos:7.1.1503
$ docker pull docker.io/centos:7.2.1511

Then we can run containerdiff.

$ ./containerdiff docker.io/centos:7.1.1503 docker.io/centos:7.2.1511 -o ./result.json -f

This command examines changes from first to second specified image, filter them and saves output to file './result.json'.

Working with containerdiff output

The output of containerdiff is JSON document. To its examining lets use python3.

First run python3 interpreter, import json module and load the result into python.

$ python3
>>> import json
>>> file = open("./result.json")
>>> result = json.load(file)

Now variable 'result' contains dictionary. Its keys should correspond to what containerdiff tests. Current implemented tests create these keys:

>>> result.keys()
dict_keys(['history', 'metadata', 'files', 'packages'])

To get an explanation for each test you can see Explanation of a format of test results and python docstrings. For example to get the documentation of history test run:

>>> import tests.history
>>> help(tests.history)
Help on module tests.history in tests:

NAME
    tests.history - Show diff in container image history.

FUNCTIONS
    dockerfile_from_image(ID, cli)
        Return list of commands used to create image *ID*. These
        commands are get from docker history.
    
    run(image1, image2, silent)
        Test history of the image.
        
        Adds one key to the output of the diff tool:
        "history" - unified_diff style changes in commands used to create
                    the image

DATA
    logger = <logging.Logger object>

FILE
    /home/mas/ContainerDiffTool/tests/history.py

Filtering

Containerdiff also offers ability to filter the output. This is a default 'filter.json' used for filtering in this example. You can specify a custom file with filtering options in '--filter' option.

{
    "files" : {
        "keys" : ["added", "removed", "modified"],
        "action" : "exclude",
        "data" : ["/var/lib/yum/yumdb",
                  "/var/lib/yum/history",
                  "/var/log/yum.log"]
    },
    "metadata" : {
        "action" : "exclude",
        "data" : ["Size",
                  "DockerVersion",
                  "Id",
                  "GraphDriver",
                  "Created",
                  "RepoTags",
                  "Parent",
                  "ContainerConfig",
                  "RepoDigests'",
                  "Container",
                  "Config:Labels:io.openshift.builder-version"]
    }
}

For each test you want to filter there have to be name/value pair in JSON object. Name specifies a name of name/value pair to filter in the result. The value have to be an object with these name/value pairs.

Name/value pair Description
"keys" : [String] Optional. Applicable to tests which result is a dict - this value specifies for which keys to apply filtering.
"action" : "include" or "exclude" Mandatory. "include" specifies that only parts of result which match "data" stays in the result. "exclude" specifies that parts of result which match "data" will be removed from result.
"data" : [String] Mandatory. Strings are regular expressions.