Feature request: Build args on docker hub

[cusspvz]

Since we can have ARGS on dockerfile, seems right to have them available on auto-builds as also (for having different tags based on the same Dockerfile)

[cheungpat]

Together with LABEL, build args is very useful to apply custom metadata to images. For example:

FROM debian:wheezy

ARG branch
LABEL com.example.branch=$branch

Setting --build-arg branch={sourceref} can add the com.example.branch=master label to the image. It would be great if Docker Hub supports more build variables to provide metadata such as build id, git commit hash, creation time etc.

[azenla]

Yes, it would be really useful. +404003

[andyneff]

I've been thinking the same thing since I started using buildargs. It would be perfect if there was a way to set specific buildargs for specific tags on my dockerhub image, instead of having to create separate tags/branches in my git repo.

[yajo]

This would be even better than #292

[cusspvz]

@yajo note that this is regarding access to set --build-args option and not entire docker build cli args.

[yajo]

Yes, I just meant that #292 could cover the same use cases, but fixing this would be much better for most of those.

[schickling]

This would make multi-version maintenance of images a lot easier

[pchico83]

This is available in Docker Cloud, which uses the same backend than Hub for autobuilds. The way to do it is to define autobuild env variables, an write a build hook that does the docker build command with the required build arguments.
https://docs.docker.com/docker-cloud/feature-reference/automated-build/
https://docs.docker.com/docker-cloud/feature-reference/automated-testing/

[nalipaz]

Can someone explain the method described by @pchico83? Because the documentation does not mention anything about writing a build hook, only hook/pre_build and hook/post_build as part of testing from what I can tell.

[pchico83]

@nalipaz although it is not documented, it is supported (I will open an issue to improve the documentation). For example, if you define an env var called VAR and you want to set it to a build argument called TEST, you can define a build hook adding a hooks/build file to the dockerfile folder:

.
..
hooks/build
Dockerfile
(other files)

whose content could be:

#!/bin/sh
docker build --build-arg TEST=$VAR -t $IMAGE_NAME .

Note that the hook is executed using the dockerfile folder as working dir, and $IMAGE_NAME is a variable we inject that corresponds with the docker tag being pushed.

[nalipaz]

That is much clearer, thanks @pchico83, and yes it would be very helpful to many I am sure were it documented. Thanks.

[Gurubol]

@pchico83, @nalipaz , Can you please provide me an example of how this hooks is used? Do we use the same docker file commands?
I tried with an example of setting an environment variable, which I later want to refer to in the Dockerfile, but it throws error

For example, in hooks/post_checkout, I added

ENV UI_BUILD x-1.2.2

But this throws me the following log.
"Executing post_checkout hook...
Unexpected error"
Can you please throw some lights on this? Any help is appreciated.

[nalipaz]

Yeah, a gist or example project would likely be helpful for this. I will see if I can find time to test and make one although I am not using this feature currently. I opted for using Travis CI to use a make file to pass in params to the build and then push the final image into docker hub.