Base and Parent Images

A Docker or OCI image is composed of layers. These layers may be inherited from another image or created during the build of a specific image as defined by the instructions in a Dockerfile or other build process.

The ancestry of an image shows the image’s parent image(s) and base image. As defined by the Docker documentation, a parent of an image is the image used to start the build of the current image, typically the image identified in the FROM directive in the Dockerfile. If the parent image is SCRATCH then the image is considered a base image.

Anchore Enterprise provides an API call to retrieve all parents and bases of an image. This call dynamically computes the ancestry set using images that have already been analyzed by the system and returns a list of image digests and their respective layers. The ancestry computation is done by matching exact layer digests between the requested image and other images in the system.

If an image X is a parent of image Y, then image X’s layers will be the first N layers of image Y where N in the number of layers in image X.

A case where an image may have multiple results in its ancestry is as follows:

A base distro image, for example debian:10:

FROM scratch
...

An application container image from that debian image, for example a node.js image let’s call mynode:latest :

FROM debian:10

# Install nodejs

The application image itself built from the framework container, let’s call it myapp:v1 :

FROM mynode:latest
COPY ./app /
...

In this case, the parent image of myapp:v1 is mynode:latest and its base is debian:10. Anchore will return each of those images with their matching layers in the API call. See the API docs for more information on the specifics of the GET /v1/enterprise/images/{digest}/ancestors API call itself.

The returned images can be used for subsequent calls to the base image comparison APIs for vulnerabilities and policy evaluations allowing you to determine which findings for an image are inherited from a specific parent or base image.

Comparing an Image with its Base or Parent

Anchore Enterprise provides a mechanism to compare the policy checks and security vulnerabilities of an image with those of a base image. This allows clients to

  • filter out results that are inherited from a base image and focus on the results relevant to the application image
  • reverse the focus and examine the base image for policy check violations and vulnerabilities which could be a deciding factor in choosing the base image for the application

To read more about the base comparison features, jump to

Last modified August 30, 2020