CODEWITHSUNDEEP
docker
James Dudley
James Dudley

Reputation: 617

Determine if docker image built locally or pulled from repo?

Is it possible to tell if a Docker image was built locally or pulled from a remote repository?

Clarification: We have large images (15+ GB) that are automated builds in Docker HUB. During development/testing it's often faster to build these images locally but using the same tags so that they can be used in building downstream images. It would be useful if we could to determine if a given image was built locally or downstream.

Upvotes: 3

Views: 1861

Answers (2)

Ahmad Abdelghany
Ahmad Abdelghany

Reputation: 13248

Given this minimal Dockerfile

From busybox
Run echo "My first command"
Run echo "My second command"
Run echo "My third command"

You can build a docker image with:

$ docker build -t abdelghany/myimage .

$ docker images
REPOSITORY                    TAG                 IMAGE ID            CREATED             SIZE
abdelghany/myimage            latest              159379ab5770        5 minutes ago       1.106 MB
busybox                       latest              c75bebcdd211        3 weeks ago         1.106 MB

Here is docker history of this locally built image:

$ docker history abdelghany/myimage
IMAGE               CREATED             CREATED BY                                      SIZE                COMMENT
7a352943082a        8 seconds ago       /bin/sh -c echo "My third command"              0 B                 
6e59deae3839        8 seconds ago       /bin/sh -c echo "My second command"             0 B                 
24df2c17994f        9 seconds ago       /bin/sh -c echo "My first command"              0 B                 
c75bebcdd211        3 weeks ago         /bin/sh -c #(nop)  CMD ["sh"]                   0 B                 
<missing>           3 weeks ago         /bin/sh -c #(nop) ADD file:5dde1d6e0f6362350d   1.106 MB

Now, push image to a registry, delete it locally, then pull it again.

$ docker push abdelghany/myimage
$ docker rmi abdelghany/myimage
$ docker pull abdelghany/myimage

Here is the docker history of the pulled image:

$ docker history abdelghany/myimage

IMAGE               CREATED             CREATED BY                                      SIZE                COMMENT
159379ab5770        3 minutes ago       /bin/sh -c echo "My third command"              0 B                 
<missing>           3 minutes ago       /bin/sh -c echo "My second command"             0 B                 
<missing>           3 minutes ago       /bin/sh -c echo "My first command"              0 B                 
<missing>           3 weeks ago         /bin/sh -c #(nop)  CMD ["sh"]                   0 B                 
<missing>           3 weeks ago         /bin/sh -c #(nop) ADD file:5dde1d6e0f6362350d   1.106 MB

Explanation: docker history shows all the commands that was used to create the image layers. For locally built images, each command is associated with an intermediate image to be used in build cache (so the next time you build the image on that docker host it uses the intermediate images from cache).

When moving images around (i.e pushing and pulling), you only move the final image so when you look at the history it shows <missing> to indicate there is no intermediate image associated with this command, which indicates it was not built on this docker host.

Upvotes: 4

gilmatic
gilmatic

Reputation: 26

You may want to see if docker history gives you the information you are looking for.

This command gives you the commands executed by the Dockerfile, so the MAINTAINERS tag (or the more correct LABEL maintainer) may appear in the history to give you some insight into the image creator.

Upvotes: 0

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